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Diffstat (limited to 'kernel/sched/ext.c')
| -rw-r--r-- | kernel/sched/ext.c | 7310 |
1 files changed, 7310 insertions, 0 deletions
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c new file mode 100644 index 000000000000..05f5a49e9649 --- /dev/null +++ b/kernel/sched/ext.c @@ -0,0 +1,7310 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst + * + * Copyright (c) 2022 Meta Platforms, Inc. and affiliates. + * Copyright (c) 2022 Tejun Heo <tj@kernel.org> + * Copyright (c) 2022 David Vernet <dvernet@meta.com> + */ +#include <linux/btf_ids.h> +#include "ext_idle.h" + +/* + * NOTE: sched_ext is in the process of growing multiple scheduler support and + * scx_root usage is in a transitional state. Naked dereferences are safe if the + * caller is one of the tasks attached to SCX and explicit RCU dereference is + * necessary otherwise. Naked scx_root dereferences trigger sparse warnings but + * are used as temporary markers to indicate that the dereferences need to be + * updated to point to the associated scheduler instances rather than scx_root. + */ +static struct scx_sched __rcu *scx_root; + +/* + * During exit, a task may schedule after losing its PIDs. When disabling the + * BPF scheduler, we need to be able to iterate tasks in every state to + * guarantee system safety. Maintain a dedicated task list which contains every + * task between its fork and eventual free. + */ +static DEFINE_RAW_SPINLOCK(scx_tasks_lock); +static LIST_HEAD(scx_tasks); + +/* ops enable/disable */ +static DEFINE_MUTEX(scx_enable_mutex); +DEFINE_STATIC_KEY_FALSE(__scx_enabled); +DEFINE_STATIC_PERCPU_RWSEM(scx_fork_rwsem); +static atomic_t scx_enable_state_var = ATOMIC_INIT(SCX_DISABLED); +static int scx_bypass_depth; +static cpumask_var_t scx_bypass_lb_donee_cpumask; +static cpumask_var_t scx_bypass_lb_resched_cpumask; +static bool scx_aborting; +static bool scx_init_task_enabled; +static bool scx_switching_all; +DEFINE_STATIC_KEY_FALSE(__scx_switched_all); + +static atomic_long_t scx_nr_rejected = ATOMIC_LONG_INIT(0); +static atomic_long_t scx_hotplug_seq = ATOMIC_LONG_INIT(0); + +/* + * A monotically increasing sequence number that is incremented every time a + * scheduler is enabled. This can be used by to check if any custom sched_ext + * scheduler has ever been used in the system. + */ +static atomic_long_t scx_enable_seq = ATOMIC_LONG_INIT(0); + +/* + * The maximum amount of time in jiffies that a task may be runnable without + * being scheduled on a CPU. If this timeout is exceeded, it will trigger + * scx_error(). + */ +static unsigned long scx_watchdog_timeout; + +/* + * The last time the delayed work was run. This delayed work relies on + * ksoftirqd being able to run to service timer interrupts, so it's possible + * that this work itself could get wedged. To account for this, we check that + * it's not stalled in the timer tick, and trigger an error if it is. + */ +static unsigned long scx_watchdog_timestamp = INITIAL_JIFFIES; + +static struct delayed_work scx_watchdog_work; + +/* + * For %SCX_KICK_WAIT: Each CPU has a pointer to an array of kick_sync sequence + * numbers. The arrays are allocated with kvzalloc() as size can exceed percpu + * allocator limits on large machines. O(nr_cpu_ids^2) allocation, allocated + * lazily when enabling and freed when disabling to avoid waste when sched_ext + * isn't active. + */ +struct scx_kick_syncs { + struct rcu_head rcu; + unsigned long syncs[]; +}; + +static DEFINE_PER_CPU(struct scx_kick_syncs __rcu *, scx_kick_syncs); + +/* + * Direct dispatch marker. + * + * Non-NULL values are used for direct dispatch from enqueue path. A valid + * pointer points to the task currently being enqueued. An ERR_PTR value is used + * to indicate that direct dispatch has already happened. + */ +static DEFINE_PER_CPU(struct task_struct *, direct_dispatch_task); + +static const struct rhashtable_params dsq_hash_params = { + .key_len = sizeof_field(struct scx_dispatch_q, id), + .key_offset = offsetof(struct scx_dispatch_q, id), + .head_offset = offsetof(struct scx_dispatch_q, hash_node), +}; + +static LLIST_HEAD(dsqs_to_free); + +/* dispatch buf */ +struct scx_dsp_buf_ent { + struct task_struct *task; + unsigned long qseq; + u64 dsq_id; + u64 enq_flags; +}; + +static u32 scx_dsp_max_batch; + +struct scx_dsp_ctx { + struct rq *rq; + u32 cursor; + u32 nr_tasks; + struct scx_dsp_buf_ent buf[]; +}; + +static struct scx_dsp_ctx __percpu *scx_dsp_ctx; + +/* string formatting from BPF */ +struct scx_bstr_buf { + u64 data[MAX_BPRINTF_VARARGS]; + char line[SCX_EXIT_MSG_LEN]; +}; + +static DEFINE_RAW_SPINLOCK(scx_exit_bstr_buf_lock); +static struct scx_bstr_buf scx_exit_bstr_buf; + +/* ops debug dump */ +struct scx_dump_data { + s32 cpu; + bool first; + s32 cursor; + struct seq_buf *s; + const char *prefix; + struct scx_bstr_buf buf; +}; + +static struct scx_dump_data scx_dump_data = { + .cpu = -1, +}; + +/* /sys/kernel/sched_ext interface */ +static struct kset *scx_kset; + +/* + * Parameters that can be adjusted through /sys/module/sched_ext/parameters. + * There usually is no reason to modify these as normal scheduler operation + * shouldn't be affected by them. The knobs are primarily for debugging. + */ +static u64 scx_slice_dfl = SCX_SLICE_DFL; +static unsigned int scx_slice_bypass_us = SCX_SLICE_BYPASS / NSEC_PER_USEC; +static unsigned int scx_bypass_lb_intv_us = SCX_BYPASS_LB_DFL_INTV_US; + +static int set_slice_us(const char *val, const struct kernel_param *kp) +{ + return param_set_uint_minmax(val, kp, 100, 100 * USEC_PER_MSEC); +} + +static const struct kernel_param_ops slice_us_param_ops = { + .set = set_slice_us, + .get = param_get_uint, +}; + +static int set_bypass_lb_intv_us(const char *val, const struct kernel_param *kp) +{ + return param_set_uint_minmax(val, kp, 0, 10 * USEC_PER_SEC); +} + +static const struct kernel_param_ops bypass_lb_intv_us_param_ops = { + .set = set_bypass_lb_intv_us, + .get = param_get_uint, +}; + +#undef MODULE_PARAM_PREFIX +#define MODULE_PARAM_PREFIX "sched_ext." + +module_param_cb(slice_bypass_us, &slice_us_param_ops, &scx_slice_bypass_us, 0600); +MODULE_PARM_DESC(slice_bypass_us, "bypass slice in microseconds, applied on [un]load (100us to 100ms)"); +module_param_cb(bypass_lb_intv_us, &bypass_lb_intv_us_param_ops, &scx_bypass_lb_intv_us, 0600); +MODULE_PARM_DESC(bypass_lb_intv_us, "bypass load balance interval in microseconds (0 (disable) to 10s)"); + +#undef MODULE_PARAM_PREFIX + +#define CREATE_TRACE_POINTS +#include <trace/events/sched_ext.h> + +static void process_ddsp_deferred_locals(struct rq *rq); +static u32 reenq_local(struct rq *rq); +static void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags); +static bool scx_vexit(struct scx_sched *sch, enum scx_exit_kind kind, + s64 exit_code, const char *fmt, va_list args); + +static __printf(4, 5) bool scx_exit(struct scx_sched *sch, + enum scx_exit_kind kind, s64 exit_code, + const char *fmt, ...) +{ + va_list args; + bool ret; + + va_start(args, fmt); + ret = scx_vexit(sch, kind, exit_code, fmt, args); + va_end(args); + + return ret; +} + +#define scx_error(sch, fmt, args...) scx_exit((sch), SCX_EXIT_ERROR, 0, fmt, ##args) +#define scx_verror(sch, fmt, args) scx_vexit((sch), SCX_EXIT_ERROR, 0, fmt, args) + +#define SCX_HAS_OP(sch, op) test_bit(SCX_OP_IDX(op), (sch)->has_op) + +static long jiffies_delta_msecs(unsigned long at, unsigned long now) +{ + if (time_after(at, now)) + return jiffies_to_msecs(at - now); + else + return -(long)jiffies_to_msecs(now - at); +} + +/* if the highest set bit is N, return a mask with bits [N+1, 31] set */ +static u32 higher_bits(u32 flags) +{ + return ~((1 << fls(flags)) - 1); +} + +/* return the mask with only the highest bit set */ +static u32 highest_bit(u32 flags) +{ + int bit = fls(flags); + return ((u64)1 << bit) >> 1; +} + +static bool u32_before(u32 a, u32 b) +{ + return (s32)(a - b) < 0; +} + +static struct scx_dispatch_q *find_global_dsq(struct scx_sched *sch, + struct task_struct *p) +{ + return sch->global_dsqs[cpu_to_node(task_cpu(p))]; +} + +static struct scx_dispatch_q *find_user_dsq(struct scx_sched *sch, u64 dsq_id) +{ + return rhashtable_lookup(&sch->dsq_hash, &dsq_id, dsq_hash_params); +} + +static const struct sched_class *scx_setscheduler_class(struct task_struct *p) +{ + if (p->sched_class == &stop_sched_class) + return &stop_sched_class; + + return __setscheduler_class(p->policy, p->prio); +} + +/* + * scx_kf_mask enforcement. Some kfuncs can only be called from specific SCX + * ops. When invoking SCX ops, SCX_CALL_OP[_RET]() should be used to indicate + * the allowed kfuncs and those kfuncs should use scx_kf_allowed() to check + * whether it's running from an allowed context. + * + * @mask is constant, always inline to cull the mask calculations. + */ +static __always_inline void scx_kf_allow(u32 mask) +{ + /* nesting is allowed only in increasing scx_kf_mask order */ + WARN_ONCE((mask | higher_bits(mask)) & current->scx.kf_mask, + "invalid nesting current->scx.kf_mask=0x%x mask=0x%x\n", + current->scx.kf_mask, mask); + current->scx.kf_mask |= mask; + barrier(); +} + +static void scx_kf_disallow(u32 mask) +{ + barrier(); + current->scx.kf_mask &= ~mask; +} + +/* + * Track the rq currently locked. + * + * This allows kfuncs to safely operate on rq from any scx ops callback, + * knowing which rq is already locked. + */ +DEFINE_PER_CPU(struct rq *, scx_locked_rq_state); + +static inline void update_locked_rq(struct rq *rq) +{ + /* + * Check whether @rq is actually locked. This can help expose bugs + * or incorrect assumptions about the context in which a kfunc or + * callback is executed. + */ + if (rq) + lockdep_assert_rq_held(rq); + __this_cpu_write(scx_locked_rq_state, rq); +} + +#define SCX_CALL_OP(sch, mask, op, rq, args...) \ +do { \ + if (rq) \ + update_locked_rq(rq); \ + if (mask) { \ + scx_kf_allow(mask); \ + (sch)->ops.op(args); \ + scx_kf_disallow(mask); \ + } else { \ + (sch)->ops.op(args); \ + } \ + if (rq) \ + update_locked_rq(NULL); \ +} while (0) + +#define SCX_CALL_OP_RET(sch, mask, op, rq, args...) \ +({ \ + __typeof__((sch)->ops.op(args)) __ret; \ + \ + if (rq) \ + update_locked_rq(rq); \ + if (mask) { \ + scx_kf_allow(mask); \ + __ret = (sch)->ops.op(args); \ + scx_kf_disallow(mask); \ + } else { \ + __ret = (sch)->ops.op(args); \ + } \ + if (rq) \ + update_locked_rq(NULL); \ + __ret; \ +}) + +/* + * Some kfuncs are allowed only on the tasks that are subjects of the + * in-progress scx_ops operation for, e.g., locking guarantees. To enforce such + * restrictions, the following SCX_CALL_OP_*() variants should be used when + * invoking scx_ops operations that take task arguments. These can only be used + * for non-nesting operations due to the way the tasks are tracked. + * + * kfuncs which can only operate on such tasks can in turn use + * scx_kf_allowed_on_arg_tasks() to test whether the invocation is allowed on + * the specific task. + */ +#define SCX_CALL_OP_TASK(sch, mask, op, rq, task, args...) \ +do { \ + BUILD_BUG_ON((mask) & ~__SCX_KF_TERMINAL); \ + current->scx.kf_tasks[0] = task; \ + SCX_CALL_OP((sch), mask, op, rq, task, ##args); \ + current->scx.kf_tasks[0] = NULL; \ +} while (0) + +#define SCX_CALL_OP_TASK_RET(sch, mask, op, rq, task, args...) \ +({ \ + __typeof__((sch)->ops.op(task, ##args)) __ret; \ + BUILD_BUG_ON((mask) & ~__SCX_KF_TERMINAL); \ + current->scx.kf_tasks[0] = task; \ + __ret = SCX_CALL_OP_RET((sch), mask, op, rq, task, ##args); \ + current->scx.kf_tasks[0] = NULL; \ + __ret; \ +}) + +#define SCX_CALL_OP_2TASKS_RET(sch, mask, op, rq, task0, task1, args...) \ +({ \ + __typeof__((sch)->ops.op(task0, task1, ##args)) __ret; \ + BUILD_BUG_ON((mask) & ~__SCX_KF_TERMINAL); \ + current->scx.kf_tasks[0] = task0; \ + current->scx.kf_tasks[1] = task1; \ + __ret = SCX_CALL_OP_RET((sch), mask, op, rq, task0, task1, ##args); \ + current->scx.kf_tasks[0] = NULL; \ + current->scx.kf_tasks[1] = NULL; \ + __ret; \ +}) + +/* @mask is constant, always inline to cull unnecessary branches */ +static __always_inline bool scx_kf_allowed(struct scx_sched *sch, u32 mask) +{ + if (unlikely(!(current->scx.kf_mask & mask))) { + scx_error(sch, "kfunc with mask 0x%x called from an operation only allowing 0x%x", + mask, current->scx.kf_mask); + return false; + } + + /* + * Enforce nesting boundaries. e.g. A kfunc which can be called from + * DISPATCH must not be called if we're running DEQUEUE which is nested + * inside ops.dispatch(). We don't need to check boundaries for any + * blocking kfuncs as the verifier ensures they're only called from + * sleepable progs. + */ + if (unlikely(highest_bit(mask) == SCX_KF_CPU_RELEASE && + (current->scx.kf_mask & higher_bits(SCX_KF_CPU_RELEASE)))) { + scx_error(sch, "cpu_release kfunc called from a nested operation"); + return false; + } + + if (unlikely(highest_bit(mask) == SCX_KF_DISPATCH && + (current->scx.kf_mask & higher_bits(SCX_KF_DISPATCH)))) { + scx_error(sch, "dispatch kfunc called from a nested operation"); + return false; + } + + return true; +} + +/* see SCX_CALL_OP_TASK() */ +static __always_inline bool scx_kf_allowed_on_arg_tasks(struct scx_sched *sch, + u32 mask, + struct task_struct *p) +{ + if (!scx_kf_allowed(sch, mask)) + return false; + + if (unlikely((p != current->scx.kf_tasks[0] && + p != current->scx.kf_tasks[1]))) { + scx_error(sch, "called on a task not being operated on"); + return false; + } + + return true; +} + +/** + * nldsq_next_task - Iterate to the next task in a non-local DSQ + * @dsq: user dsq being iterated + * @cur: current position, %NULL to start iteration + * @rev: walk backwards + * + * Returns %NULL when iteration is finished. + */ +static struct task_struct *nldsq_next_task(struct scx_dispatch_q *dsq, + struct task_struct *cur, bool rev) +{ + struct list_head *list_node; + struct scx_dsq_list_node *dsq_lnode; + + lockdep_assert_held(&dsq->lock); + + if (cur) + list_node = &cur->scx.dsq_list.node; + else + list_node = &dsq->list; + + /* find the next task, need to skip BPF iteration cursors */ + do { + if (rev) + list_node = list_node->prev; + else + list_node = list_node->next; + + if (list_node == &dsq->list) + return NULL; + + dsq_lnode = container_of(list_node, struct scx_dsq_list_node, + node); + } while (dsq_lnode->flags & SCX_DSQ_LNODE_ITER_CURSOR); + + return container_of(dsq_lnode, struct task_struct, scx.dsq_list); +} + +#define nldsq_for_each_task(p, dsq) \ + for ((p) = nldsq_next_task((dsq), NULL, false); (p); \ + (p) = nldsq_next_task((dsq), (p), false)) + + +/* + * BPF DSQ iterator. Tasks in a non-local DSQ can be iterated in [reverse] + * dispatch order. BPF-visible iterator is opaque and larger to allow future + * changes without breaking backward compatibility. Can be used with + * bpf_for_each(). See bpf_iter_scx_dsq_*(). + */ +enum scx_dsq_iter_flags { + /* iterate in the reverse dispatch order */ + SCX_DSQ_ITER_REV = 1U << 16, + + __SCX_DSQ_ITER_HAS_SLICE = 1U << 30, + __SCX_DSQ_ITER_HAS_VTIME = 1U << 31, + + __SCX_DSQ_ITER_USER_FLAGS = SCX_DSQ_ITER_REV, + __SCX_DSQ_ITER_ALL_FLAGS = __SCX_DSQ_ITER_USER_FLAGS | + __SCX_DSQ_ITER_HAS_SLICE | + __SCX_DSQ_ITER_HAS_VTIME, +}; + +struct bpf_iter_scx_dsq_kern { + struct scx_dsq_list_node cursor; + struct scx_dispatch_q *dsq; + u64 slice; + u64 vtime; +} __attribute__((aligned(8))); + +struct bpf_iter_scx_dsq { + u64 __opaque[6]; +} __attribute__((aligned(8))); + + +/* + * SCX task iterator. + */ +struct scx_task_iter { + struct sched_ext_entity cursor; + struct task_struct *locked_task; + struct rq *rq; + struct rq_flags rf; + u32 cnt; + bool list_locked; +}; + +/** + * scx_task_iter_start - Lock scx_tasks_lock and start a task iteration + * @iter: iterator to init + * + * Initialize @iter and return with scx_tasks_lock held. Once initialized, @iter + * must eventually be stopped with scx_task_iter_stop(). + * + * scx_tasks_lock and the rq lock may be released using scx_task_iter_unlock() + * between this and the first next() call or between any two next() calls. If + * the locks are released between two next() calls, the caller is responsible + * for ensuring that the task being iterated remains accessible either through + * RCU read lock or obtaining a reference count. + * + * All tasks which existed when the iteration started are guaranteed to be + * visited as long as they are not dead. + */ +static void scx_task_iter_start(struct scx_task_iter *iter) +{ + memset(iter, 0, sizeof(*iter)); + + raw_spin_lock_irq(&scx_tasks_lock); + + iter->cursor = (struct sched_ext_entity){ .flags = SCX_TASK_CURSOR }; + list_add(&iter->cursor.tasks_node, &scx_tasks); + iter->list_locked = true; +} + +static void __scx_task_iter_rq_unlock(struct scx_task_iter *iter) +{ + if (iter->locked_task) { + task_rq_unlock(iter->rq, iter->locked_task, &iter->rf); + iter->locked_task = NULL; + } +} + +/** + * scx_task_iter_unlock - Unlock rq and scx_tasks_lock held by a task iterator + * @iter: iterator to unlock + * + * If @iter is in the middle of a locked iteration, it may be locking the rq of + * the task currently being visited in addition to scx_tasks_lock. Unlock both. + * This function can be safely called anytime during an iteration. The next + * iterator operation will automatically restore the necessary locking. + */ +static void scx_task_iter_unlock(struct scx_task_iter *iter) +{ + __scx_task_iter_rq_unlock(iter); + if (iter->list_locked) { + iter->list_locked = false; + raw_spin_unlock_irq(&scx_tasks_lock); + } +} + +static void __scx_task_iter_maybe_relock(struct scx_task_iter *iter) +{ + if (!iter->list_locked) { + raw_spin_lock_irq(&scx_tasks_lock); + iter->list_locked = true; + } +} + +/** + * scx_task_iter_stop - Stop a task iteration and unlock scx_tasks_lock + * @iter: iterator to exit + * + * Exit a previously initialized @iter. Must be called with scx_tasks_lock held + * which is released on return. If the iterator holds a task's rq lock, that rq + * lock is also released. See scx_task_iter_start() for details. + */ +static void scx_task_iter_stop(struct scx_task_iter *iter) +{ + __scx_task_iter_maybe_relock(iter); + list_del_init(&iter->cursor.tasks_node); + scx_task_iter_unlock(iter); +} + +/** + * scx_task_iter_next - Next task + * @iter: iterator to walk + * + * Visit the next task. See scx_task_iter_start() for details. Locks are dropped + * and re-acquired every %SCX_TASK_ITER_BATCH iterations to avoid causing stalls + * by holding scx_tasks_lock for too long. + */ +static struct task_struct *scx_task_iter_next(struct scx_task_iter *iter) +{ + struct list_head *cursor = &iter->cursor.tasks_node; + struct sched_ext_entity *pos; + + if (!(++iter->cnt % SCX_TASK_ITER_BATCH)) { + scx_task_iter_unlock(iter); + cond_resched(); + } + + __scx_task_iter_maybe_relock(iter); + + list_for_each_entry(pos, cursor, tasks_node) { + if (&pos->tasks_node == &scx_tasks) + return NULL; + if (!(pos->flags & SCX_TASK_CURSOR)) { + list_move(cursor, &pos->tasks_node); + return container_of(pos, struct task_struct, scx); + } + } + + /* can't happen, should always terminate at scx_tasks above */ + BUG(); +} + +/** + * scx_task_iter_next_locked - Next non-idle task with its rq locked + * @iter: iterator to walk + * + * Visit the non-idle task with its rq lock held. Allows callers to specify + * whether they would like to filter out dead tasks. See scx_task_iter_start() + * for details. + */ +static struct task_struct *scx_task_iter_next_locked(struct scx_task_iter *iter) +{ + struct task_struct *p; + + __scx_task_iter_rq_unlock(iter); + + while ((p = scx_task_iter_next(iter))) { + /* + * scx_task_iter is used to prepare and move tasks into SCX + * while loading the BPF scheduler and vice-versa while + * unloading. The init_tasks ("swappers") should be excluded + * from the iteration because: + * + * - It's unsafe to use __setschduler_prio() on an init_task to + * determine the sched_class to use as it won't preserve its + * idle_sched_class. + * + * - ops.init/exit_task() can easily be confused if called with + * init_tasks as they, e.g., share PID 0. + * + * As init_tasks are never scheduled through SCX, they can be + * skipped safely. Note that is_idle_task() which tests %PF_IDLE + * doesn't work here: + * + * - %PF_IDLE may not be set for an init_task whose CPU hasn't + * yet been onlined. + * + * - %PF_IDLE can be set on tasks that are not init_tasks. See + * play_idle_precise() used by CONFIG_IDLE_INJECT. + * + * Test for idle_sched_class as only init_tasks are on it. + */ + if (p->sched_class != &idle_sched_class) + break; + } + if (!p) + return NULL; + + iter->rq = task_rq_lock(p, &iter->rf); + iter->locked_task = p; + + return p; +} + +/** + * scx_add_event - Increase an event counter for 'name' by 'cnt' + * @sch: scx_sched to account events for + * @name: an event name defined in struct scx_event_stats + * @cnt: the number of the event occurred + * + * This can be used when preemption is not disabled. + */ +#define scx_add_event(sch, name, cnt) do { \ + this_cpu_add((sch)->pcpu->event_stats.name, (cnt)); \ + trace_sched_ext_event(#name, (cnt)); \ +} while(0) + +/** + * __scx_add_event - Increase an event counter for 'name' by 'cnt' + * @sch: scx_sched to account events for + * @name: an event name defined in struct scx_event_stats + * @cnt: the number of the event occurred + * + * This should be used only when preemption is disabled. + */ +#define __scx_add_event(sch, name, cnt) do { \ + __this_cpu_add((sch)->pcpu->event_stats.name, (cnt)); \ + trace_sched_ext_event(#name, cnt); \ +} while(0) + +/** + * scx_agg_event - Aggregate an event counter 'kind' from 'src_e' to 'dst_e' + * @dst_e: destination event stats + * @src_e: source event stats + * @kind: a kind of event to be aggregated + */ +#define scx_agg_event(dst_e, src_e, kind) do { \ + (dst_e)->kind += READ_ONCE((src_e)->kind); \ +} while(0) + +/** + * scx_dump_event - Dump an event 'kind' in 'events' to 's' + * @s: output seq_buf + * @events: event stats + * @kind: a kind of event to dump + */ +#define scx_dump_event(s, events, kind) do { \ + dump_line(&(s), "%40s: %16lld", #kind, (events)->kind); \ +} while (0) + + +static void scx_read_events(struct scx_sched *sch, + struct scx_event_stats *events); + +static enum scx_enable_state scx_enable_state(void) +{ + return atomic_read(&scx_enable_state_var); +} + +static enum scx_enable_state scx_set_enable_state(enum scx_enable_state to) +{ + return atomic_xchg(&scx_enable_state_var, to); +} + +static bool scx_tryset_enable_state(enum scx_enable_state to, + enum scx_enable_state from) +{ + int from_v = from; + + return atomic_try_cmpxchg(&scx_enable_state_var, &from_v, to); +} + +/** + * wait_ops_state - Busy-wait the specified ops state to end + * @p: target task + * @opss: state to wait the end of + * + * Busy-wait for @p to transition out of @opss. This can only be used when the + * state part of @opss is %SCX_QUEUEING or %SCX_DISPATCHING. This function also + * has load_acquire semantics to ensure that the caller can see the updates made + * in the enqueueing and dispatching paths. + */ +static void wait_ops_state(struct task_struct *p, unsigned long opss) +{ + do { + cpu_relax(); + } while (atomic_long_read_acquire(&p->scx.ops_state) == opss); +} + +static inline bool __cpu_valid(s32 cpu) +{ + return likely(cpu >= 0 && cpu < nr_cpu_ids && cpu_possible(cpu)); +} + +/** + * ops_cpu_valid - Verify a cpu number, to be used on ops input args + * @sch: scx_sched to abort on error + * @cpu: cpu number which came from a BPF ops + * @where: extra information reported on error + * + * @cpu is a cpu number which came from the BPF scheduler and can be any value. + * Verify that it is in range and one of the possible cpus. If invalid, trigger + * an ops error. + */ +static bool ops_cpu_valid(struct scx_sched *sch, s32 cpu, const char *where) +{ + if (__cpu_valid(cpu)) { + return true; + } else { + scx_error(sch, "invalid CPU %d%s%s", cpu, where ? " " : "", where ?: ""); + return false; + } +} + +/** + * ops_sanitize_err - Sanitize a -errno value + * @sch: scx_sched to error out on error + * @ops_name: operation to blame on failure + * @err: -errno value to sanitize + * + * Verify @err is a valid -errno. If not, trigger scx_error() and return + * -%EPROTO. This is necessary because returning a rogue -errno up the chain can + * cause misbehaviors. For an example, a large negative return from + * ops.init_task() triggers an oops when passed up the call chain because the + * value fails IS_ERR() test after being encoded with ERR_PTR() and then is + * handled as a pointer. + */ +static int ops_sanitize_err(struct scx_sched *sch, const char *ops_name, s32 err) +{ + if (err < 0 && err >= -MAX_ERRNO) + return err; + + scx_error(sch, "ops.%s() returned an invalid errno %d", ops_name, err); + return -EPROTO; +} + +static void run_deferred(struct rq *rq) +{ + process_ddsp_deferred_locals(rq); + + if (local_read(&rq->scx.reenq_local_deferred)) { + local_set(&rq->scx.reenq_local_deferred, 0); + reenq_local(rq); + } +} + +static void deferred_bal_cb_workfn(struct rq *rq) +{ + run_deferred(rq); +} + +static void deferred_irq_workfn(struct irq_work *irq_work) +{ + struct rq *rq = container_of(irq_work, struct rq, scx.deferred_irq_work); + + raw_spin_rq_lock(rq); + run_deferred(rq); + raw_spin_rq_unlock(rq); +} + +/** + * schedule_deferred - Schedule execution of deferred actions on an rq + * @rq: target rq + * + * Schedule execution of deferred actions on @rq. Deferred actions are executed + * with @rq locked but unpinned, and thus can unlock @rq to e.g. migrate tasks + * to other rqs. + */ +static void schedule_deferred(struct rq *rq) +{ + /* + * Queue an irq work. They are executed on IRQ re-enable which may take + * a bit longer than the scheduler hook in schedule_deferred_locked(). + */ + irq_work_queue(&rq->scx.deferred_irq_work); +} + +/** + * schedule_deferred_locked - Schedule execution of deferred actions on an rq + * @rq: target rq + * + * Schedule execution of deferred actions on @rq. Equivalent to + * schedule_deferred() but requires @rq to be locked and can be more efficient. + */ +static void schedule_deferred_locked(struct rq *rq) +{ + lockdep_assert_rq_held(rq); + + /* + * If in the middle of waking up a task, task_woken_scx() will be called + * afterwards which will then run the deferred actions, no need to + * schedule anything. + */ + if (rq->scx.flags & SCX_RQ_IN_WAKEUP) + return; + + /* Don't do anything if there already is a deferred operation. */ + if (rq->scx.flags & SCX_RQ_BAL_CB_PENDING) + return; + + /* + * If in balance, the balance callbacks will be called before rq lock is + * released. Schedule one. + * + * + * We can't directly insert the callback into the + * rq's list: The call can drop its lock and make the pending balance + * callback visible to unrelated code paths that call rq_pin_lock(). + * + * Just let balance_one() know that it must do it itself. + */ + if (rq->scx.flags & SCX_RQ_IN_BALANCE) { + rq->scx.flags |= SCX_RQ_BAL_CB_PENDING; + return; + } + + /* + * No scheduler hooks available. Use the generic irq_work path. The + * above WAKEUP and BALANCE paths should cover most of the cases and the + * time to IRQ re-enable shouldn't be long. + */ + schedule_deferred(rq); +} + +/** + * touch_core_sched - Update timestamp used for core-sched task ordering + * @rq: rq to read clock from, must be locked + * @p: task to update the timestamp for + * + * Update @p->scx.core_sched_at timestamp. This is used by scx_prio_less() to + * implement global or local-DSQ FIFO ordering for core-sched. Should be called + * when a task becomes runnable and its turn on the CPU ends (e.g. slice + * exhaustion). + */ +static void touch_core_sched(struct rq *rq, struct task_struct *p) +{ + lockdep_assert_rq_held(rq); + +#ifdef CONFIG_SCHED_CORE + /* + * It's okay to update the timestamp spuriously. Use + * sched_core_disabled() which is cheaper than enabled(). + * + * As this is used to determine ordering between tasks of sibling CPUs, + * it may be better to use per-core dispatch sequence instead. + */ + if (!sched_core_disabled()) + p->scx.core_sched_at = sched_clock_cpu(cpu_of(rq)); +#endif +} + +/** + * touch_core_sched_dispatch - Update core-sched timestamp on dispatch + * @rq: rq to read clock from, must be locked + * @p: task being dispatched + * + * If the BPF scheduler implements custom core-sched ordering via + * ops.core_sched_before(), @p->scx.core_sched_at is used to implement FIFO + * ordering within each local DSQ. This function is called from dispatch paths + * and updates @p->scx.core_sched_at if custom core-sched ordering is in effect. + */ +static void touch_core_sched_dispatch(struct rq *rq, struct task_struct *p) +{ + lockdep_assert_rq_held(rq); + +#ifdef CONFIG_SCHED_CORE + if (unlikely(SCX_HAS_OP(scx_root, core_sched_before))) + touch_core_sched(rq, p); +#endif +} + +static void update_curr_scx(struct rq *rq) +{ + struct task_struct *curr = rq->curr; + s64 delta_exec; + + delta_exec = update_curr_common(rq); + if (unlikely(delta_exec <= 0)) + return; + + if (curr->scx.slice != SCX_SLICE_INF) { + curr->scx.slice -= min_t(u64, curr->scx.slice, delta_exec); + if (!curr->scx.slice) + touch_core_sched(rq, curr); + } +} + +static bool scx_dsq_priq_less(struct rb_node *node_a, + const struct rb_node *node_b) +{ + const struct task_struct *a = + container_of(node_a, struct task_struct, scx.dsq_priq); + const struct task_struct *b = + container_of(node_b, struct task_struct, scx.dsq_priq); + + return time_before64(a->scx.dsq_vtime, b->scx.dsq_vtime); +} + +static void dsq_mod_nr(struct scx_dispatch_q *dsq, s32 delta) +{ + /* scx_bpf_dsq_nr_queued() reads ->nr without locking, use WRITE_ONCE() */ + WRITE_ONCE(dsq->nr, dsq->nr + delta); +} + +static void refill_task_slice_dfl(struct scx_sched *sch, struct task_struct *p) +{ + p->scx.slice = READ_ONCE(scx_slice_dfl); + __scx_add_event(sch, SCX_EV_REFILL_SLICE_DFL, 1); +} + +static void dispatch_enqueue(struct scx_sched *sch, struct scx_dispatch_q *dsq, + struct task_struct *p, u64 enq_flags) +{ + bool is_local = dsq->id == SCX_DSQ_LOCAL; + + WARN_ON_ONCE(p->scx.dsq || !list_empty(&p->scx.dsq_list.node)); + WARN_ON_ONCE((p->scx.dsq_flags & SCX_TASK_DSQ_ON_PRIQ) || + !RB_EMPTY_NODE(&p->scx.dsq_priq)); + + if (!is_local) { + raw_spin_lock_nested(&dsq->lock, + (enq_flags & SCX_ENQ_NESTED) ? SINGLE_DEPTH_NESTING : 0); + + if (unlikely(dsq->id == SCX_DSQ_INVALID)) { + scx_error(sch, "attempting to dispatch to a destroyed dsq"); + /* fall back to the global dsq */ + raw_spin_unlock(&dsq->lock); + dsq = find_global_dsq(sch, p); + raw_spin_lock(&dsq->lock); + } + } + + if (unlikely((dsq->id & SCX_DSQ_FLAG_BUILTIN) && + (enq_flags & SCX_ENQ_DSQ_PRIQ))) { + /* + * SCX_DSQ_LOCAL and SCX_DSQ_GLOBAL DSQs always consume from + * their FIFO queues. To avoid confusion and accidentally + * starving vtime-dispatched tasks by FIFO-dispatched tasks, we + * disallow any internal DSQ from doing vtime ordering of + * tasks. + */ + scx_error(sch, "cannot use vtime ordering for built-in DSQs"); + enq_flags &= ~SCX_ENQ_DSQ_PRIQ; + } + + if (enq_flags & SCX_ENQ_DSQ_PRIQ) { + struct rb_node *rbp; + + /* + * A PRIQ DSQ shouldn't be using FIFO enqueueing. As tasks are + * linked to both the rbtree and list on PRIQs, this can only be + * tested easily when adding the first task. + */ + if (unlikely(RB_EMPTY_ROOT(&dsq->priq) && + nldsq_next_task(dsq, NULL, false))) + scx_error(sch, "DSQ ID 0x%016llx already had FIFO-enqueued tasks", + dsq->id); + + p->scx.dsq_flags |= SCX_TASK_DSQ_ON_PRIQ; + rb_add(&p->scx.dsq_priq, &dsq->priq, scx_dsq_priq_less); + + /* + * Find the previous task and insert after it on the list so + * that @dsq->list is vtime ordered. + */ + rbp = rb_prev(&p->scx.dsq_priq); + if (rbp) { + struct task_struct *prev = + container_of(rbp, struct task_struct, + scx.dsq_priq); + list_add(&p->scx.dsq_list.node, &prev->scx.dsq_list.node); + /* first task unchanged - no update needed */ + } else { + list_add(&p->scx.dsq_list.node, &dsq->list); + /* not builtin and new task is at head - use fastpath */ + rcu_assign_pointer(dsq->first_task, p); + } + } else { + /* a FIFO DSQ shouldn't be using PRIQ enqueuing */ + if (unlikely(!RB_EMPTY_ROOT(&dsq->priq))) + scx_error(sch, "DSQ ID 0x%016llx already had PRIQ-enqueued tasks", + dsq->id); + + if (enq_flags & (SCX_ENQ_HEAD | SCX_ENQ_PREEMPT)) { + list_add(&p->scx.dsq_list.node, &dsq->list); + /* new task inserted at head - use fastpath */ + if (!(dsq->id & SCX_DSQ_FLAG_BUILTIN)) + rcu_assign_pointer(dsq->first_task, p); + } else { + bool was_empty; + + was_empty = list_empty(&dsq->list); + list_add_tail(&p->scx.dsq_list.node, &dsq->list); + if (was_empty && !(dsq->id & SCX_DSQ_FLAG_BUILTIN)) + rcu_assign_pointer(dsq->first_task, p); + } + } + + /* seq records the order tasks are queued, used by BPF DSQ iterator */ + dsq->seq++; + p->scx.dsq_seq = dsq->seq; + + dsq_mod_nr(dsq, 1); + p->scx.dsq = dsq; + + /* + * scx.ddsp_dsq_id and scx.ddsp_enq_flags are only relevant on the + * direct dispatch path, but we clear them here because the direct + * dispatch verdict may be overridden on the enqueue path during e.g. + * bypass. + */ + p->scx.ddsp_dsq_id = SCX_DSQ_INVALID; + p->scx.ddsp_enq_flags = 0; + + /* + * We're transitioning out of QUEUEING or DISPATCHING. store_release to + * match waiters' load_acquire. + */ + if (enq_flags & SCX_ENQ_CLEAR_OPSS) + atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE); + + if (is_local) { + struct rq *rq = container_of(dsq, struct rq, scx.local_dsq); + bool preempt = false; + + if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->curr && + rq->curr->sched_class == &ext_sched_class) { + rq->curr->scx.slice = 0; + preempt = true; + } + + if (preempt || sched_class_above(&ext_sched_class, + rq->curr->sched_class)) + resched_curr(rq); + } else { + raw_spin_unlock(&dsq->lock); + } +} + +static void task_unlink_from_dsq(struct task_struct *p, + struct scx_dispatch_q *dsq) +{ + WARN_ON_ONCE(list_empty(&p->scx.dsq_list.node)); + + if (p->scx.dsq_flags & SCX_TASK_DSQ_ON_PRIQ) { + rb_erase(&p->scx.dsq_priq, &dsq->priq); + RB_CLEAR_NODE(&p->scx.dsq_priq); + p->scx.dsq_flags &= ~SCX_TASK_DSQ_ON_PRIQ; + } + + list_del_init(&p->scx.dsq_list.node); + dsq_mod_nr(dsq, -1); + + if (!(dsq->id & SCX_DSQ_FLAG_BUILTIN) && dsq->first_task == p) { + struct task_struct *first_task; + + first_task = nldsq_next_task(dsq, NULL, false); + rcu_assign_pointer(dsq->first_task, first_task); + } +} + +static void dispatch_dequeue(struct rq *rq, struct task_struct *p) +{ + struct scx_dispatch_q *dsq = p->scx.dsq; + bool is_local = dsq == &rq->scx.local_dsq; + + lockdep_assert_rq_held(rq); + + if (!dsq) { + /* + * If !dsq && on-list, @p is on @rq's ddsp_deferred_locals. + * Unlinking is all that's needed to cancel. + */ + if (unlikely(!list_empty(&p->scx.dsq_list.node))) + list_del_init(&p->scx.dsq_list.node); + + /* + * When dispatching directly from the BPF scheduler to a local + * DSQ, the task isn't associated with any DSQ but + * @p->scx.holding_cpu may be set under the protection of + * %SCX_OPSS_DISPATCHING. + */ + if (p->scx.holding_cpu >= 0) + p->scx.holding_cpu = -1; + + return; + } + + if (!is_local) + raw_spin_lock(&dsq->lock); + + /* + * Now that we hold @dsq->lock, @p->holding_cpu and @p->scx.dsq_* can't + * change underneath us. + */ + if (p->scx.holding_cpu < 0) { + /* @p must still be on @dsq, dequeue */ + task_unlink_from_dsq(p, dsq); + } else { + /* + * We're racing against dispatch_to_local_dsq() which already + * removed @p from @dsq and set @p->scx.holding_cpu. Clear the + * holding_cpu which tells dispatch_to_local_dsq() that it lost + * the race. + */ + WARN_ON_ONCE(!list_empty(&p->scx.dsq_list.node)); + p->scx.holding_cpu = -1; + } + p->scx.dsq = NULL; + + if (!is_local) + raw_spin_unlock(&dsq->lock); +} + +/* + * Abbreviated version of dispatch_dequeue() that can be used when both @p's rq + * and dsq are locked. + */ +static void dispatch_dequeue_locked(struct task_struct *p, + struct scx_dispatch_q *dsq) +{ + lockdep_assert_rq_held(task_rq(p)); + lockdep_assert_held(&dsq->lock); + + task_unlink_from_dsq(p, dsq); + p->scx.dsq = NULL; +} + +static struct scx_dispatch_q *find_dsq_for_dispatch(struct scx_sched *sch, + struct rq *rq, u64 dsq_id, + struct task_struct *p) +{ + struct scx_dispatch_q *dsq; + + if (dsq_id == SCX_DSQ_LOCAL) + return &rq->scx.local_dsq; + + if ((dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON) { + s32 cpu = dsq_id & SCX_DSQ_LOCAL_CPU_MASK; + + if (!ops_cpu_valid(sch, cpu, "in SCX_DSQ_LOCAL_ON dispatch verdict")) + return find_global_dsq(sch, p); + + return &cpu_rq(cpu)->scx.local_dsq; + } + + if (dsq_id == SCX_DSQ_GLOBAL) + dsq = find_global_dsq(sch, p); + else + dsq = find_user_dsq(sch, dsq_id); + + if (unlikely(!dsq)) { + scx_error(sch, "non-existent DSQ 0x%llx for %s[%d]", + dsq_id, p->comm, p->pid); + return find_global_dsq(sch, p); + } + + return dsq; +} + +static void mark_direct_dispatch(struct scx_sched *sch, + struct task_struct *ddsp_task, + struct task_struct *p, u64 dsq_id, + u64 enq_flags) +{ + /* + * Mark that dispatch already happened from ops.select_cpu() or + * ops.enqueue() by spoiling direct_dispatch_task with a non-NULL value + * which can never match a valid task pointer. + */ + __this_cpu_write(direct_dispatch_task, ERR_PTR(-ESRCH)); + + /* @p must match the task on the enqueue path */ + if (unlikely(p != ddsp_task)) { + if (IS_ERR(ddsp_task)) + scx_error(sch, "%s[%d] already direct-dispatched", + p->comm, p->pid); + else + scx_error(sch, "scheduling for %s[%d] but trying to direct-dispatch %s[%d]", + ddsp_task->comm, ddsp_task->pid, + p->comm, p->pid); + return; + } + + WARN_ON_ONCE(p->scx.ddsp_dsq_id != SCX_DSQ_INVALID); + WARN_ON_ONCE(p->scx.ddsp_enq_flags); + + p->scx.ddsp_dsq_id = dsq_id; + p->scx.ddsp_enq_flags = enq_flags; +} + +static void direct_dispatch(struct scx_sched *sch, struct task_struct *p, + u64 enq_flags) +{ + struct rq *rq = task_rq(p); + struct scx_dispatch_q *dsq = + find_dsq_for_dispatch(sch, rq, p->scx.ddsp_dsq_id, p); + + touch_core_sched_dispatch(rq, p); + + p->scx.ddsp_enq_flags |= enq_flags; + + /* + * We are in the enqueue path with @rq locked and pinned, and thus can't + * double lock a remote rq and enqueue to its local DSQ. For + * DSQ_LOCAL_ON verdicts targeting the local DSQ of a remote CPU, defer + * the enqueue so that it's executed when @rq can be unlocked. + */ + if (dsq->id == SCX_DSQ_LOCAL && dsq != &rq->scx.local_dsq) { + unsigned long opss; + + opss = atomic_long_read(&p->scx.ops_state) & SCX_OPSS_STATE_MASK; + + switch (opss & SCX_OPSS_STATE_MASK) { + case SCX_OPSS_NONE: + break; + case SCX_OPSS_QUEUEING: + /* + * As @p was never passed to the BPF side, _release is + * not strictly necessary. Still do it for consistency. + */ + atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE); + break; + default: + WARN_ONCE(true, "sched_ext: %s[%d] has invalid ops state 0x%lx in direct_dispatch()", + p->comm, p->pid, opss); + atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE); + break; + } + + WARN_ON_ONCE(p->scx.dsq || !list_empty(&p->scx.dsq_list.node)); + list_add_tail(&p->scx.dsq_list.node, + &rq->scx.ddsp_deferred_locals); + schedule_deferred_locked(rq); + return; + } + + dispatch_enqueue(sch, dsq, p, + p->scx.ddsp_enq_flags | SCX_ENQ_CLEAR_OPSS); +} + +static bool scx_rq_online(struct rq *rq) +{ + /* + * Test both cpu_active() and %SCX_RQ_ONLINE. %SCX_RQ_ONLINE indicates + * the online state as seen from the BPF scheduler. cpu_active() test + * guarantees that, if this function returns %true, %SCX_RQ_ONLINE will + * stay set until the current scheduling operation is complete even if + * we aren't locking @rq. + */ + return likely((rq->scx.flags & SCX_RQ_ONLINE) && cpu_active(cpu_of(rq))); +} + +static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags, + int sticky_cpu) +{ + struct scx_sched *sch = scx_root; + struct task_struct **ddsp_taskp; + struct scx_dispatch_q *dsq; + unsigned long qseq; + + WARN_ON_ONCE(!(p->scx.flags & SCX_TASK_QUEUED)); + + /* rq migration */ + if (sticky_cpu == cpu_of(rq)) + goto local_norefill; + + /* + * If !scx_rq_online(), we already told the BPF scheduler that the CPU + * is offline and are just running the hotplug path. Don't bother the + * BPF scheduler. + */ + if (!scx_rq_online(rq)) + goto local; + + if (scx_rq_bypassing(rq)) { + __scx_add_event(sch, SCX_EV_BYPASS_DISPATCH, 1); + goto bypass; + } + + if (p->scx.ddsp_dsq_id != SCX_DSQ_INVALID) + goto direct; + + /* see %SCX_OPS_ENQ_EXITING */ + if (!(sch->ops.flags & SCX_OPS_ENQ_EXITING) && + unlikely(p->flags & PF_EXITING)) { + __scx_add_event(sch, SCX_EV_ENQ_SKIP_EXITING, 1); + goto local; + } + + /* see %SCX_OPS_ENQ_MIGRATION_DISABLED */ + if (!(sch->ops.flags & SCX_OPS_ENQ_MIGRATION_DISABLED) && + is_migration_disabled(p)) { + __scx_add_event(sch, SCX_EV_ENQ_SKIP_MIGRATION_DISABLED, 1); + goto local; + } + + if (unlikely(!SCX_HAS_OP(sch, enqueue))) + goto global; + + /* DSQ bypass didn't trigger, enqueue on the BPF scheduler */ + qseq = rq->scx.ops_qseq++ << SCX_OPSS_QSEQ_SHIFT; + + WARN_ON_ONCE(atomic_long_read(&p->scx.ops_state) != SCX_OPSS_NONE); + atomic_long_set(&p->scx.ops_state, SCX_OPSS_QUEUEING | qseq); + + ddsp_taskp = this_cpu_ptr(&direct_dispatch_task); + WARN_ON_ONCE(*ddsp_taskp); + *ddsp_taskp = p; + + SCX_CALL_OP_TASK(sch, SCX_KF_ENQUEUE, enqueue, rq, p, enq_flags); + + *ddsp_taskp = NULL; + if (p->scx.ddsp_dsq_id != SCX_DSQ_INVALID) + goto direct; + + /* + * If not directly dispatched, QUEUEING isn't clear yet and dispatch or + * dequeue may be waiting. The store_release matches their load_acquire. + */ + atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_QUEUED | qseq); + return; + +direct: + direct_dispatch(sch, p, enq_flags); + return; +local_norefill: + dispatch_enqueue(sch, &rq->scx.local_dsq, p, enq_flags); + return; +local: + dsq = &rq->scx.local_dsq; + goto enqueue; +global: + dsq = find_global_dsq(sch, p); + goto enqueue; +bypass: + dsq = &task_rq(p)->scx.bypass_dsq; + goto enqueue; + +enqueue: + /* + * For task-ordering, slice refill must be treated as implying the end + * of the current slice. Otherwise, the longer @p stays on the CPU, the + * higher priority it becomes from scx_prio_less()'s POV. + */ + touch_core_sched(rq, p); + refill_task_slice_dfl(sch, p); + dispatch_enqueue(sch, dsq, p, enq_flags); +} + +static bool task_runnable(const struct task_struct *p) +{ + return !list_empty(&p->scx.runnable_node); +} + +static void set_task_runnable(struct rq *rq, struct task_struct *p) +{ + lockdep_assert_rq_held(rq); + + if (p->scx.flags & SCX_TASK_RESET_RUNNABLE_AT) { + p->scx.runnable_at = jiffies; + p->scx.flags &= ~SCX_TASK_RESET_RUNNABLE_AT; + } + + /* + * list_add_tail() must be used. scx_bypass() depends on tasks being + * appended to the runnable_list. + */ + list_add_tail(&p->scx.runnable_node, &rq->scx.runnable_list); +} + +static void clr_task_runnable(struct task_struct *p, bool reset_runnable_at) +{ + list_del_init(&p->scx.runnable_node); + if (reset_runnable_at) + p->scx.flags |= SCX_TASK_RESET_RUNNABLE_AT; +} + +static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int enq_flags) +{ + struct scx_sched *sch = scx_root; + int sticky_cpu = p->scx.sticky_cpu; + + if (enq_flags & ENQUEUE_WAKEUP) + rq->scx.flags |= SCX_RQ_IN_WAKEUP; + + enq_flags |= rq->scx.extra_enq_flags; + + if (sticky_cpu >= 0) + p->scx.sticky_cpu = -1; + + /* + * Restoring a running task will be immediately followed by + * set_next_task_scx() which expects the task to not be on the BPF + * scheduler as tasks can only start running through local DSQs. Force + * direct-dispatch into the local DSQ by setting the sticky_cpu. + */ + if (unlikely(enq_flags & ENQUEUE_RESTORE) && task_current(rq, p)) + sticky_cpu = cpu_of(rq); + + if (p->scx.flags & SCX_TASK_QUEUED) { + WARN_ON_ONCE(!task_runnable(p)); + goto out; + } + + set_task_runnable(rq, p); + p->scx.flags |= SCX_TASK_QUEUED; + rq->scx.nr_running++; + add_nr_running(rq, 1); + + if (SCX_HAS_OP(sch, runnable) && !task_on_rq_migrating(p)) + SCX_CALL_OP_TASK(sch, SCX_KF_REST, runnable, rq, p, enq_flags); + + if (enq_flags & SCX_ENQ_WAKEUP) + touch_core_sched(rq, p); + + do_enqueue_task(rq, p, enq_flags, sticky_cpu); +out: + rq->scx.flags &= ~SCX_RQ_IN_WAKEUP; + + if ((enq_flags & SCX_ENQ_CPU_SELECTED) && + unlikely(cpu_of(rq) != p->scx.selected_cpu)) + __scx_add_event(sch, SCX_EV_SELECT_CPU_FALLBACK, 1); +} + +static void ops_dequeue(struct rq *rq, struct task_struct *p, u64 deq_flags) +{ + struct scx_sched *sch = scx_root; + unsigned long opss; + + /* dequeue is always temporary, don't reset runnable_at */ + clr_task_runnable(p, false); + + /* acquire ensures that we see the preceding updates on QUEUED */ + opss = atomic_long_read_acquire(&p->scx.ops_state); + + switch (opss & SCX_OPSS_STATE_MASK) { + case SCX_OPSS_NONE: + break; + case SCX_OPSS_QUEUEING: + /* + * QUEUEING is started and finished while holding @p's rq lock. + * As we're holding the rq lock now, we shouldn't see QUEUEING. + */ + BUG(); + case SCX_OPSS_QUEUED: + if (SCX_HAS_OP(sch, dequeue)) + SCX_CALL_OP_TASK(sch, SCX_KF_REST, dequeue, rq, + p, deq_flags); + + if (atomic_long_try_cmpxchg(&p->scx.ops_state, &opss, + SCX_OPSS_NONE)) + break; + fallthrough; + case SCX_OPSS_DISPATCHING: + /* + * If @p is being dispatched from the BPF scheduler to a DSQ, + * wait for the transfer to complete so that @p doesn't get + * added to its DSQ after dequeueing is complete. + * + * As we're waiting on DISPATCHING with the rq locked, the + * dispatching side shouldn't try to lock the rq while + * DISPATCHING is set. See dispatch_to_local_dsq(). + * + * DISPATCHING shouldn't have qseq set and control can reach + * here with NONE @opss from the above QUEUED case block. + * Explicitly wait on %SCX_OPSS_DISPATCHING instead of @opss. + */ + wait_ops_state(p, SCX_OPSS_DISPATCHING); + BUG_ON(atomic_long_read(&p->scx.ops_state) != SCX_OPSS_NONE); + break; + } +} + +static bool dequeue_task_scx(struct rq *rq, struct task_struct *p, int deq_flags) +{ + struct scx_sched *sch = scx_root; + + if (!(p->scx.flags & SCX_TASK_QUEUED)) { + WARN_ON_ONCE(task_runnable(p)); + return true; + } + + ops_dequeue(rq, p, deq_flags); + + /* + * A currently running task which is going off @rq first gets dequeued + * and then stops running. As we want running <-> stopping transitions + * to be contained within runnable <-> quiescent transitions, trigger + * ->stopping() early here instead of in put_prev_task_scx(). + * + * @p may go through multiple stopping <-> running transitions between + * here and put_prev_task_scx() if task attribute changes occur while + * balance_scx() leaves @rq unlocked. However, they don't contain any + * information meaningful to the BPF scheduler and can be suppressed by + * skipping the callbacks if the task is !QUEUED. + */ + if (SCX_HAS_OP(sch, stopping) && task_current(rq, p)) { + update_curr_scx(rq); + SCX_CALL_OP_TASK(sch, SCX_KF_REST, stopping, rq, p, false); + } + + if (SCX_HAS_OP(sch, quiescent) && !task_on_rq_migrating(p)) + SCX_CALL_OP_TASK(sch, SCX_KF_REST, quiescent, rq, p, deq_flags); + + if (deq_flags & SCX_DEQ_SLEEP) + p->scx.flags |= SCX_TASK_DEQD_FOR_SLEEP; + else + p->scx.flags &= ~SCX_TASK_DEQD_FOR_SLEEP; + + p->scx.flags &= ~SCX_TASK_QUEUED; + rq->scx.nr_running--; + sub_nr_running(rq, 1); + + dispatch_dequeue(rq, p); + return true; +} + +static void yield_task_scx(struct rq *rq) +{ + struct scx_sched *sch = scx_root; + struct task_struct *p = rq->donor; + + if (SCX_HAS_OP(sch, yield)) + SCX_CALL_OP_2TASKS_RET(sch, SCX_KF_REST, yield, rq, p, NULL); + else + p->scx.slice = 0; +} + +static bool yield_to_task_scx(struct rq *rq, struct task_struct *to) +{ + struct scx_sched *sch = scx_root; + struct task_struct *from = rq->donor; + + if (SCX_HAS_OP(sch, yield)) + return SCX_CALL_OP_2TASKS_RET(sch, SCX_KF_REST, yield, rq, + from, to); + else + return false; +} + +static void move_local_task_to_local_dsq(struct task_struct *p, u64 enq_flags, + struct scx_dispatch_q *src_dsq, + struct rq *dst_rq) +{ + struct scx_dispatch_q *dst_dsq = &dst_rq->scx.local_dsq; + + /* @dsq is locked and @p is on @dst_rq */ + lockdep_assert_held(&src_dsq->lock); + lockdep_assert_rq_held(dst_rq); + + WARN_ON_ONCE(p->scx.holding_cpu >= 0); + + if (enq_flags & (SCX_ENQ_HEAD | SCX_ENQ_PREEMPT)) + list_add(&p->scx.dsq_list.node, &dst_dsq->list); + else + list_add_tail(&p->scx.dsq_list.node, &dst_dsq->list); + + dsq_mod_nr(dst_dsq, 1); + p->scx.dsq = dst_dsq; +} + +/** + * move_remote_task_to_local_dsq - Move a task from a foreign rq to a local DSQ + * @p: task to move + * @enq_flags: %SCX_ENQ_* + * @src_rq: rq to move the task from, locked on entry, released on return + * @dst_rq: rq to move the task into, locked on return + * + * Move @p which is currently on @src_rq to @dst_rq's local DSQ. + */ +static void move_remote_task_to_local_dsq(struct task_struct *p, u64 enq_flags, + struct rq *src_rq, struct rq *dst_rq) +{ + lockdep_assert_rq_held(src_rq); + + /* the following marks @p MIGRATING which excludes dequeue */ + deactivate_task(src_rq, p, 0); + set_task_cpu(p, cpu_of(dst_rq)); + p->scx.sticky_cpu = cpu_of(dst_rq); + + raw_spin_rq_unlock(src_rq); + raw_spin_rq_lock(dst_rq); + + /* + * We want to pass scx-specific enq_flags but activate_task() will + * truncate the upper 32 bit. As we own @rq, we can pass them through + * @rq->scx.extra_enq_flags instead. + */ + WARN_ON_ONCE(!cpumask_test_cpu(cpu_of(dst_rq), p->cpus_ptr)); + WARN_ON_ONCE(dst_rq->scx.extra_enq_flags); + dst_rq->scx.extra_enq_flags = enq_flags; + activate_task(dst_rq, p, 0); + dst_rq->scx.extra_enq_flags = 0; +} + +/* + * Similar to kernel/sched/core.c::is_cpu_allowed(). However, there are two + * differences: + * + * - is_cpu_allowed() asks "Can this task run on this CPU?" while + * task_can_run_on_remote_rq() asks "Can the BPF scheduler migrate the task to + * this CPU?". + * + * While migration is disabled, is_cpu_allowed() has to say "yes" as the task + * must be allowed to finish on the CPU that it's currently on regardless of + * the CPU state. However, task_can_run_on_remote_rq() must say "no" as the + * BPF scheduler shouldn't attempt to migrate a task which has migration + * disabled. + * + * - The BPF scheduler is bypassed while the rq is offline and we can always say + * no to the BPF scheduler initiated migrations while offline. + * + * The caller must ensure that @p and @rq are on different CPUs. + */ +static bool task_can_run_on_remote_rq(struct scx_sched *sch, + struct task_struct *p, struct rq *rq, + bool enforce) +{ + int cpu = cpu_of(rq); + + WARN_ON_ONCE(task_cpu(p) == cpu); + + /* + * If @p has migration disabled, @p->cpus_ptr is updated to contain only + * the pinned CPU in migrate_disable_switch() while @p is being switched + * out. However, put_prev_task_scx() is called before @p->cpus_ptr is + * updated and thus another CPU may see @p on a DSQ inbetween leading to + * @p passing the below task_allowed_on_cpu() check while migration is + * disabled. + * + * Test the migration disabled state first as the race window is narrow + * and the BPF scheduler failing to check migration disabled state can + * easily be masked if task_allowed_on_cpu() is done first. + */ + if (unlikely(is_migration_disabled(p))) { + if (enforce) + scx_error(sch, "SCX_DSQ_LOCAL[_ON] cannot move migration disabled %s[%d] from CPU %d to %d", + p->comm, p->pid, task_cpu(p), cpu); + return false; + } + + /* + * We don't require the BPF scheduler to avoid dispatching to offline + * CPUs mostly for convenience but also because CPUs can go offline + * between scx_bpf_dsq_insert() calls and here. Trigger error iff the + * picked CPU is outside the allowed mask. + */ + if (!task_allowed_on_cpu(p, cpu)) { + if (enforce) + scx_error(sch, "SCX_DSQ_LOCAL[_ON] target CPU %d not allowed for %s[%d]", + cpu, p->comm, p->pid); + return false; + } + + if (!scx_rq_online(rq)) { + if (enforce) + __scx_add_event(sch, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE, 1); + return false; + } + + return true; +} + +/** + * unlink_dsq_and_lock_src_rq() - Unlink task from its DSQ and lock its task_rq + * @p: target task + * @dsq: locked DSQ @p is currently on + * @src_rq: rq @p is currently on, stable with @dsq locked + * + * Called with @dsq locked but no rq's locked. We want to move @p to a different + * DSQ, including any local DSQ, but are not locking @src_rq. Locking @src_rq is + * required when transferring into a local DSQ. Even when transferring into a + * non-local DSQ, it's better to use the same mechanism to protect against + * dequeues and maintain the invariant that @p->scx.dsq can only change while + * @src_rq is locked, which e.g. scx_dump_task() depends on. + * + * We want to grab @src_rq but that can deadlock if we try while locking @dsq, + * so we want to unlink @p from @dsq, drop its lock and then lock @src_rq. As + * this may race with dequeue, which can't drop the rq lock or fail, do a little + * dancing from our side. + * + * @p->scx.holding_cpu is set to this CPU before @dsq is unlocked. If @p gets + * dequeued after we unlock @dsq but before locking @src_rq, the holding_cpu + * would be cleared to -1. While other cpus may have updated it to different + * values afterwards, as this operation can't be preempted or recurse, the + * holding_cpu can never become this CPU again before we're done. Thus, we can + * tell whether we lost to dequeue by testing whether the holding_cpu still + * points to this CPU. See dispatch_dequeue() for the counterpart. + * + * On return, @dsq is unlocked and @src_rq is locked. Returns %true if @p is + * still valid. %false if lost to dequeue. + */ +static bool unlink_dsq_and_lock_src_rq(struct task_struct *p, + struct scx_dispatch_q *dsq, + struct rq *src_rq) +{ + s32 cpu = raw_smp_processor_id(); + + lockdep_assert_held(&dsq->lock); + + WARN_ON_ONCE(p->scx.holding_cpu >= 0); + task_unlink_from_dsq(p, dsq); + p->scx.holding_cpu = cpu; + + raw_spin_unlock(&dsq->lock); + raw_spin_rq_lock(src_rq); + + /* task_rq couldn't have changed if we're still the holding cpu */ + return likely(p->scx.holding_cpu == cpu) && + !WARN_ON_ONCE(src_rq != task_rq(p)); +} + +static bool consume_remote_task(struct rq *this_rq, struct task_struct *p, + struct scx_dispatch_q *dsq, struct rq *src_rq) +{ + raw_spin_rq_unlock(this_rq); + + if (unlink_dsq_and_lock_src_rq(p, dsq, src_rq)) { + move_remote_task_to_local_dsq(p, 0, src_rq, this_rq); + return true; + } else { + raw_spin_rq_unlock(src_rq); + raw_spin_rq_lock(this_rq); + return false; + } +} + +/** + * move_task_between_dsqs() - Move a task from one DSQ to another + * @sch: scx_sched being operated on + * @p: target task + * @enq_flags: %SCX_ENQ_* + * @src_dsq: DSQ @p is currently on, must not be a local DSQ + * @dst_dsq: DSQ @p is being moved to, can be any DSQ + * + * Must be called with @p's task_rq and @src_dsq locked. If @dst_dsq is a local + * DSQ and @p is on a different CPU, @p will be migrated and thus its task_rq + * will change. As @p's task_rq is locked, this function doesn't need to use the + * holding_cpu mechanism. + * + * On return, @src_dsq is unlocked and only @p's new task_rq, which is the + * return value, is locked. + */ +static struct rq *move_task_between_dsqs(struct scx_sched *sch, + struct task_struct *p, u64 enq_flags, + struct scx_dispatch_q *src_dsq, + struct scx_dispatch_q *dst_dsq) +{ + struct rq *src_rq = task_rq(p), *dst_rq; + + BUG_ON(src_dsq->id == SCX_DSQ_LOCAL); + lockdep_assert_held(&src_dsq->lock); + lockdep_assert_rq_held(src_rq); + + if (dst_dsq->id == SCX_DSQ_LOCAL) { + dst_rq = container_of(dst_dsq, struct rq, scx.local_dsq); + if (src_rq != dst_rq && + unlikely(!task_can_run_on_remote_rq(sch, p, dst_rq, true))) { + dst_dsq = find_global_dsq(sch, p); + dst_rq = src_rq; + } + } else { + /* no need to migrate if destination is a non-local DSQ */ + dst_rq = src_rq; + } + + /* + * Move @p into $dst_dsq. If $dst_dsq is the local DSQ of a different + * CPU, @p will be migrated. + */ + if (dst_dsq->id == SCX_DSQ_LOCAL) { + /* @p is going from a non-local DSQ to a local DSQ */ + if (src_rq == dst_rq) { + task_unlink_from_dsq(p, src_dsq); + move_local_task_to_local_dsq(p, enq_flags, + src_dsq, dst_rq); + raw_spin_unlock(&src_dsq->lock); + } else { + raw_spin_unlock(&src_dsq->lock); + move_remote_task_to_local_dsq(p, enq_flags, + src_rq, dst_rq); + } + } else { + /* + * @p is going from a non-local DSQ to a non-local DSQ. As + * $src_dsq is already locked, do an abbreviated dequeue. + */ + dispatch_dequeue_locked(p, src_dsq); + raw_spin_unlock(&src_dsq->lock); + + dispatch_enqueue(sch, dst_dsq, p, enq_flags); + } + + return dst_rq; +} + +static bool consume_dispatch_q(struct scx_sched *sch, struct rq *rq, + struct scx_dispatch_q *dsq) +{ + struct task_struct *p; +retry: + /* + * The caller can't expect to successfully consume a task if the task's + * addition to @dsq isn't guaranteed to be visible somehow. Test + * @dsq->list without locking and skip if it seems empty. + */ + if (list_empty(&dsq->list)) + return false; + + raw_spin_lock(&dsq->lock); + + nldsq_for_each_task(p, dsq) { + struct rq *task_rq = task_rq(p); + + /* + * This loop can lead to multiple lockup scenarios, e.g. the BPF + * scheduler can put an enormous number of affinitized tasks into + * a contended DSQ, or the outer retry loop can repeatedly race + * against scx_bypass() dequeueing tasks from @dsq trying to put + * the system into the bypass mode. This can easily live-lock the + * machine. If aborting, exit from all non-bypass DSQs. + */ + if (unlikely(READ_ONCE(scx_aborting)) && dsq->id != SCX_DSQ_BYPASS) + break; + + if (rq == task_rq) { + task_unlink_from_dsq(p, dsq); + move_local_task_to_local_dsq(p, 0, dsq, rq); + raw_spin_unlock(&dsq->lock); + return true; + } + + if (task_can_run_on_remote_rq(sch, p, rq, false)) { + if (likely(consume_remote_task(rq, p, dsq, task_rq))) + return true; + goto retry; + } + } + + raw_spin_unlock(&dsq->lock); + return false; +} + +static bool consume_global_dsq(struct scx_sched *sch, struct rq *rq) +{ + int node = cpu_to_node(cpu_of(rq)); + + return consume_dispatch_q(sch, rq, sch->global_dsqs[node]); +} + +/** + * dispatch_to_local_dsq - Dispatch a task to a local dsq + * @sch: scx_sched being operated on + * @rq: current rq which is locked + * @dst_dsq: destination DSQ + * @p: task to dispatch + * @enq_flags: %SCX_ENQ_* + * + * We're holding @rq lock and want to dispatch @p to @dst_dsq which is a local + * DSQ. This function performs all the synchronization dancing needed because + * local DSQs are protected with rq locks. + * + * The caller must have exclusive ownership of @p (e.g. through + * %SCX_OPSS_DISPATCHING). + */ +static void dispatch_to_local_dsq(struct scx_sched *sch, struct rq *rq, + struct scx_dispatch_q *dst_dsq, + struct task_struct *p, u64 enq_flags) +{ + struct rq *src_rq = task_rq(p); + struct rq *dst_rq = container_of(dst_dsq, struct rq, scx.local_dsq); + struct rq *locked_rq = rq; + + /* + * We're synchronized against dequeue through DISPATCHING. As @p can't + * be dequeued, its task_rq and cpus_allowed are stable too. + * + * If dispatching to @rq that @p is already on, no lock dancing needed. + */ + if (rq == src_rq && rq == dst_rq) { + dispatch_enqueue(sch, dst_dsq, p, + enq_flags | SCX_ENQ_CLEAR_OPSS); + return; + } + + if (src_rq != dst_rq && + unlikely(!task_can_run_on_remote_rq(sch, p, dst_rq, true))) { + dispatch_enqueue(sch, find_global_dsq(sch, p), p, + enq_flags | SCX_ENQ_CLEAR_OPSS); + return; + } + + /* + * @p is on a possibly remote @src_rq which we need to lock to move the + * task. If dequeue is in progress, it'd be locking @src_rq and waiting + * on DISPATCHING, so we can't grab @src_rq lock while holding + * DISPATCHING. + * + * As DISPATCHING guarantees that @p is wholly ours, we can pretend that + * we're moving from a DSQ and use the same mechanism - mark the task + * under transfer with holding_cpu, release DISPATCHING and then follow + * the same protocol. See unlink_dsq_and_lock_src_rq(). + */ + p->scx.holding_cpu = raw_smp_processor_id(); + + /* store_release ensures that dequeue sees the above */ + atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE); + + /* switch to @src_rq lock */ + if (locked_rq != src_rq) { + raw_spin_rq_unlock(locked_rq); + locked_rq = src_rq; + raw_spin_rq_lock(src_rq); + } + + /* task_rq couldn't have changed if we're still the holding cpu */ + if (likely(p->scx.holding_cpu == raw_smp_processor_id()) && + !WARN_ON_ONCE(src_rq != task_rq(p))) { + /* + * If @p is staying on the same rq, there's no need to go + * through the full deactivate/activate cycle. Optimize by + * abbreviating move_remote_task_to_local_dsq(). + */ + if (src_rq == dst_rq) { + p->scx.holding_cpu = -1; + dispatch_enqueue(sch, &dst_rq->scx.local_dsq, p, + enq_flags); + } else { + move_remote_task_to_local_dsq(p, enq_flags, + src_rq, dst_rq); + /* task has been moved to dst_rq, which is now locked */ + locked_rq = dst_rq; + } + + /* if the destination CPU is idle, wake it up */ + if (sched_class_above(p->sched_class, dst_rq->curr->sched_class)) + resched_curr(dst_rq); + } + + /* switch back to @rq lock */ + if (locked_rq != rq) { + raw_spin_rq_unlock(locked_rq); + raw_spin_rq_lock(rq); + } +} + +/** + * finish_dispatch - Asynchronously finish dispatching a task + * @rq: current rq which is locked + * @p: task to finish dispatching + * @qseq_at_dispatch: qseq when @p started getting dispatched + * @dsq_id: destination DSQ ID + * @enq_flags: %SCX_ENQ_* + * + * Dispatching to local DSQs may need to wait for queueing to complete or + * require rq lock dancing. As we don't wanna do either while inside + * ops.dispatch() to avoid locking order inversion, we split dispatching into + * two parts. scx_bpf_dsq_insert() which is called by ops.dispatch() records the + * task and its qseq. Once ops.dispatch() returns, this function is called to + * finish up. + * + * There is no guarantee that @p is still valid for dispatching or even that it + * was valid in the first place. Make sure that the task is still owned by the + * BPF scheduler and claim the ownership before dispatching. + */ +static void finish_dispatch(struct scx_sched *sch, struct rq *rq, + struct task_struct *p, + unsigned long qseq_at_dispatch, + u64 dsq_id, u64 enq_flags) +{ + struct scx_dispatch_q *dsq; + unsigned long opss; + + touch_core_sched_dispatch(rq, p); +retry: + /* + * No need for _acquire here. @p is accessed only after a successful + * try_cmpxchg to DISPATCHING. + */ + opss = atomic_long_read(&p->scx.ops_state); + + switch (opss & SCX_OPSS_STATE_MASK) { + case SCX_OPSS_DISPATCHING: + case SCX_OPSS_NONE: + /* someone else already got to it */ + return; + case SCX_OPSS_QUEUED: + /* + * If qseq doesn't match, @p has gone through at least one + * dispatch/dequeue and re-enqueue cycle between + * scx_bpf_dsq_insert() and here and we have no claim on it. + */ + if ((opss & SCX_OPSS_QSEQ_MASK) != qseq_at_dispatch) + return; + + /* + * While we know @p is accessible, we don't yet have a claim on + * it - the BPF scheduler is allowed to dispatch tasks + * spuriously and there can be a racing dequeue attempt. Let's + * claim @p by atomically transitioning it from QUEUED to + * DISPATCHING. + */ + if (likely(atomic_long_try_cmpxchg(&p->scx.ops_state, &opss, + SCX_OPSS_DISPATCHING))) + break; + goto retry; + case SCX_OPSS_QUEUEING: + /* + * do_enqueue_task() is in the process of transferring the task + * to the BPF scheduler while holding @p's rq lock. As we aren't + * holding any kernel or BPF resource that the enqueue path may + * depend upon, it's safe to wait. + */ + wait_ops_state(p, opss); + goto retry; + } + + BUG_ON(!(p->scx.flags & SCX_TASK_QUEUED)); + + dsq = find_dsq_for_dispatch(sch, this_rq(), dsq_id, p); + + if (dsq->id == SCX_DSQ_LOCAL) + dispatch_to_local_dsq(sch, rq, dsq, p, enq_flags); + else + dispatch_enqueue(sch, dsq, p, enq_flags | SCX_ENQ_CLEAR_OPSS); +} + +static void flush_dispatch_buf(struct scx_sched *sch, struct rq *rq) +{ + struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx); + u32 u; + + for (u = 0; u < dspc->cursor; u++) { + struct scx_dsp_buf_ent *ent = &dspc->buf[u]; + + finish_dispatch(sch, rq, ent->task, ent->qseq, ent->dsq_id, + ent->enq_flags); + } + + dspc->nr_tasks += dspc->cursor; + dspc->cursor = 0; +} + +static inline void maybe_queue_balance_callback(struct rq *rq) +{ + lockdep_assert_rq_held(rq); + + if (!(rq->scx.flags & SCX_RQ_BAL_CB_PENDING)) + return; + + queue_balance_callback(rq, &rq->scx.deferred_bal_cb, + deferred_bal_cb_workfn); + + rq->scx.flags &= ~SCX_RQ_BAL_CB_PENDING; +} + +static int balance_one(struct rq *rq, struct task_struct *prev) +{ + struct scx_sched *sch = scx_root; + struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx); + bool prev_on_scx = prev->sched_class == &ext_sched_class; + bool prev_on_rq = prev->scx.flags & SCX_TASK_QUEUED; + int nr_loops = SCX_DSP_MAX_LOOPS; + + lockdep_assert_rq_held(rq); + rq->scx.flags |= SCX_RQ_IN_BALANCE; + rq->scx.flags &= ~SCX_RQ_BAL_KEEP; + + if ((sch->ops.flags & SCX_OPS_HAS_CPU_PREEMPT) && + unlikely(rq->scx.cpu_released)) { + /* + * If the previous sched_class for the current CPU was not SCX, + * notify the BPF scheduler that it again has control of the + * core. This callback complements ->cpu_release(), which is + * emitted in switch_class(). + */ + if (SCX_HAS_OP(sch, cpu_acquire)) + SCX_CALL_OP(sch, SCX_KF_REST, cpu_acquire, rq, + cpu_of(rq), NULL); + rq->scx.cpu_released = false; + } + + if (prev_on_scx) { + update_curr_scx(rq); + + /* + * If @prev is runnable & has slice left, it has priority and + * fetching more just increases latency for the fetched tasks. + * Tell pick_task_scx() to keep running @prev. If the BPF + * scheduler wants to handle this explicitly, it should + * implement ->cpu_release(). + * + * See scx_disable_workfn() for the explanation on the bypassing + * test. + */ + if (prev_on_rq && prev->scx.slice && !scx_rq_bypassing(rq)) { + rq->scx.flags |= SCX_RQ_BAL_KEEP; + goto has_tasks; + } + } + + /* if there already are tasks to run, nothing to do */ + if (rq->scx.local_dsq.nr) + goto has_tasks; + + if (consume_global_dsq(sch, rq)) + goto has_tasks; + + if (scx_rq_bypassing(rq)) { + if (consume_dispatch_q(sch, rq, &rq->scx.bypass_dsq)) + goto has_tasks; + else + goto no_tasks; + } + + if (unlikely(!SCX_HAS_OP(sch, dispatch)) || !scx_rq_online(rq)) + goto no_tasks; + + dspc->rq = rq; + + /* + * The dispatch loop. Because flush_dispatch_buf() may drop the rq lock, + * the local DSQ might still end up empty after a successful + * ops.dispatch(). If the local DSQ is empty even after ops.dispatch() + * produced some tasks, retry. The BPF scheduler may depend on this + * looping behavior to simplify its implementation. + */ + do { + dspc->nr_tasks = 0; + + SCX_CALL_OP(sch, SCX_KF_DISPATCH, dispatch, rq, + cpu_of(rq), prev_on_scx ? prev : NULL); + + flush_dispatch_buf(sch, rq); + + if (prev_on_rq && prev->scx.slice) { + rq->scx.flags |= SCX_RQ_BAL_KEEP; + goto has_tasks; + } + if (rq->scx.local_dsq.nr) + goto has_tasks; + if (consume_global_dsq(sch, rq)) + goto has_tasks; + + /* + * ops.dispatch() can trap us in this loop by repeatedly + * dispatching ineligible tasks. Break out once in a while to + * allow the watchdog to run. As IRQ can't be enabled in + * balance(), we want to complete this scheduling cycle and then + * start a new one. IOW, we want to call resched_curr() on the + * next, most likely idle, task, not the current one. Use + * scx_kick_cpu() for deferred kicking. + */ + if (unlikely(!--nr_loops)) { + scx_kick_cpu(sch, cpu_of(rq), 0); + break; + } + } while (dspc->nr_tasks); + +no_tasks: + /* + * Didn't find another task to run. Keep running @prev unless + * %SCX_OPS_ENQ_LAST is in effect. + */ + if (prev_on_rq && + (!(sch->ops.flags & SCX_OPS_ENQ_LAST) || scx_rq_bypassing(rq))) { + rq->scx.flags |= SCX_RQ_BAL_KEEP; + __scx_add_event(sch, SCX_EV_DISPATCH_KEEP_LAST, 1); + goto has_tasks; + } + rq->scx.flags &= ~SCX_RQ_IN_BALANCE; + return false; + +has_tasks: + rq->scx.flags &= ~SCX_RQ_IN_BALANCE; + return true; +} + +static void process_ddsp_deferred_locals(struct rq *rq) +{ + struct task_struct *p; + + lockdep_assert_rq_held(rq); + + /* + * Now that @rq can be unlocked, execute the deferred enqueueing of + * tasks directly dispatched to the local DSQs of other CPUs. See + * direct_dispatch(). Keep popping from the head instead of using + * list_for_each_entry_safe() as dispatch_local_dsq() may unlock @rq + * temporarily. + */ + while ((p = list_first_entry_or_null(&rq->scx.ddsp_deferred_locals, + struct task_struct, scx.dsq_list.node))) { + struct scx_sched *sch = scx_root; + struct scx_dispatch_q *dsq; + + list_del_init(&p->scx.dsq_list.node); + + dsq = find_dsq_for_dispatch(sch, rq, p->scx.ddsp_dsq_id, p); + if (!WARN_ON_ONCE(dsq->id != SCX_DSQ_LOCAL)) + dispatch_to_local_dsq(sch, rq, dsq, p, + p->scx.ddsp_enq_flags); + } +} + +static void set_next_task_scx(struct rq *rq, struct task_struct *p, bool first) +{ + struct scx_sched *sch = scx_root; + + if (p->scx.flags & SCX_TASK_QUEUED) { + /* + * Core-sched might decide to execute @p before it is + * dispatched. Call ops_dequeue() to notify the BPF scheduler. + */ + ops_dequeue(rq, p, SCX_DEQ_CORE_SCHED_EXEC); + dispatch_dequeue(rq, p); + } + + p->se.exec_start = rq_clock_task(rq); + + /* see dequeue_task_scx() on why we skip when !QUEUED */ + if (SCX_HAS_OP(sch, running) && (p->scx.flags & SCX_TASK_QUEUED)) + SCX_CALL_OP_TASK(sch, SCX_KF_REST, running, rq, p); + + clr_task_runnable(p, true); + + /* + * @p is getting newly scheduled or got kicked after someone updated its + * slice. Refresh whether tick can be stopped. See scx_can_stop_tick(). + */ + if ((p->scx.slice == SCX_SLICE_INF) != + (bool)(rq->scx.flags & SCX_RQ_CAN_STOP_TICK)) { + if (p->scx.slice == SCX_SLICE_INF) + rq->scx.flags |= SCX_RQ_CAN_STOP_TICK; + else + rq->scx.flags &= ~SCX_RQ_CAN_STOP_TICK; + + sched_update_tick_dependency(rq); + + /* + * For now, let's refresh the load_avgs just when transitioning + * in and out of nohz. In the future, we might want to add a + * mechanism which calls the following periodically on + * tick-stopped CPUs. + */ + update_other_load_avgs(rq); + } +} + +static enum scx_cpu_preempt_reason +preempt_reason_from_class(const struct sched_class *class) +{ + if (class == &stop_sched_class) + return SCX_CPU_PREEMPT_STOP; + if (class == &dl_sched_class) + return SCX_CPU_PREEMPT_DL; + if (class == &rt_sched_class) + return SCX_CPU_PREEMPT_RT; + return SCX_CPU_PREEMPT_UNKNOWN; +} + +static void switch_class(struct rq *rq, struct task_struct *next) +{ + struct scx_sched *sch = scx_root; + const struct sched_class *next_class = next->sched_class; + + if (!(sch->ops.flags & SCX_OPS_HAS_CPU_PREEMPT)) + return; + + /* + * The callback is conceptually meant to convey that the CPU is no + * longer under the control of SCX. Therefore, don't invoke the callback + * if the next class is below SCX (in which case the BPF scheduler has + * actively decided not to schedule any tasks on the CPU). + */ + if (sched_class_above(&ext_sched_class, next_class)) + return; + + /* + * At this point we know that SCX was preempted by a higher priority + * sched_class, so invoke the ->cpu_release() callback if we have not + * done so already. We only send the callback once between SCX being + * preempted, and it regaining control of the CPU. + * + * ->cpu_release() complements ->cpu_acquire(), which is emitted the + * next time that balance_scx() is invoked. + */ + if (!rq->scx.cpu_released) { + if (SCX_HAS_OP(sch, cpu_release)) { + struct scx_cpu_release_args args = { + .reason = preempt_reason_from_class(next_class), + .task = next, + }; + + SCX_CALL_OP(sch, SCX_KF_CPU_RELEASE, cpu_release, rq, + cpu_of(rq), &args); + } + rq->scx.cpu_released = true; + } +} + +static void put_prev_task_scx(struct rq *rq, struct task_struct *p, + struct task_struct *next) +{ + struct scx_sched *sch = scx_root; + + /* see kick_cpus_irq_workfn() */ + smp_store_release(&rq->scx.kick_sync, rq->scx.kick_sync + 1); + + update_curr_scx(rq); + + /* see dequeue_task_scx() on why we skip when !QUEUED */ + if (SCX_HAS_OP(sch, stopping) && (p->scx.flags & SCX_TASK_QUEUED)) + SCX_CALL_OP_TASK(sch, SCX_KF_REST, stopping, rq, p, true); + + if (p->scx.flags & SCX_TASK_QUEUED) { + set_task_runnable(rq, p); + + /* + * If @p has slice left and is being put, @p is getting + * preempted by a higher priority scheduler class or core-sched + * forcing a different task. Leave it at the head of the local + * DSQ. + */ + if (p->scx.slice && !scx_rq_bypassing(rq)) { + dispatch_enqueue(sch, &rq->scx.local_dsq, p, + SCX_ENQ_HEAD); + goto switch_class; + } + + /* + * If @p is runnable but we're about to enter a lower + * sched_class, %SCX_OPS_ENQ_LAST must be set. Tell + * ops.enqueue() that @p is the only one available for this cpu, + * which should trigger an explicit follow-up scheduling event. + */ + if (sched_class_above(&ext_sched_class, next->sched_class)) { + WARN_ON_ONCE(!(sch->ops.flags & SCX_OPS_ENQ_LAST)); + do_enqueue_task(rq, p, SCX_ENQ_LAST, -1); + } else { + do_enqueue_task(rq, p, 0, -1); + } + } + +switch_class: + if (next && next->sched_class != &ext_sched_class) + switch_class(rq, next); +} + +static struct task_struct *first_local_task(struct rq *rq) +{ + return list_first_entry_or_null(&rq->scx.local_dsq.list, + struct task_struct, scx.dsq_list.node); +} + +static struct task_struct * +do_pick_task_scx(struct rq *rq, struct rq_flags *rf, bool force_scx) +{ + struct task_struct *prev = rq->curr; + bool keep_prev, kick_idle = false; + struct task_struct *p; + + /* see kick_cpus_irq_workfn() */ + smp_store_release(&rq->scx.kick_sync, rq->scx.kick_sync + 1); + + rq_modified_clear(rq); + + rq_unpin_lock(rq, rf); + balance_one(rq, prev); + rq_repin_lock(rq, rf); + maybe_queue_balance_callback(rq); + + /* + * If any higher-priority sched class enqueued a runnable task on + * this rq during balance_one(), abort and return RETRY_TASK, so + * that the scheduler loop can restart. + * + * If @force_scx is true, always try to pick a SCHED_EXT task, + * regardless of any higher-priority sched classes activity. + */ + if (!force_scx && rq_modified_above(rq, &ext_sched_class)) + return RETRY_TASK; + + keep_prev = rq->scx.flags & SCX_RQ_BAL_KEEP; + if (unlikely(keep_prev && + prev->sched_class != &ext_sched_class)) { + WARN_ON_ONCE(scx_enable_state() == SCX_ENABLED); + keep_prev = false; + } + + /* + * If balance_scx() is telling us to keep running @prev, replenish slice + * if necessary and keep running @prev. Otherwise, pop the first one + * from the local DSQ. + */ + if (keep_prev) { + p = prev; + if (!p->scx.slice) + refill_task_slice_dfl(rcu_dereference_sched(scx_root), p); + } else { + p = first_local_task(rq); + if (!p) { + if (kick_idle) + scx_kick_cpu(rcu_dereference_sched(scx_root), + cpu_of(rq), SCX_KICK_IDLE); + return NULL; + } + + if (unlikely(!p->scx.slice)) { + struct scx_sched *sch = rcu_dereference_sched(scx_root); + + if (!scx_rq_bypassing(rq) && !sch->warned_zero_slice) { + printk_deferred(KERN_WARNING "sched_ext: %s[%d] has zero slice in %s()\n", + p->comm, p->pid, __func__); + sch->warned_zero_slice = true; + } + refill_task_slice_dfl(sch, p); + } + } + + return p; +} + +static struct task_struct *pick_task_scx(struct rq *rq, struct rq_flags *rf) +{ + return do_pick_task_scx(rq, rf, false); +} + +#ifdef CONFIG_SCHED_CORE +/** + * scx_prio_less - Task ordering for core-sched + * @a: task A + * @b: task B + * @in_fi: in forced idle state + * + * Core-sched is implemented as an additional scheduling layer on top of the + * usual sched_class'es and needs to find out the expected task ordering. For + * SCX, core-sched calls this function to interrogate the task ordering. + * + * Unless overridden by ops.core_sched_before(), @p->scx.core_sched_at is used + * to implement the default task ordering. The older the timestamp, the higher + * priority the task - the global FIFO ordering matching the default scheduling + * behavior. + * + * When ops.core_sched_before() is enabled, @p->scx.core_sched_at is used to + * implement FIFO ordering within each local DSQ. See pick_task_scx(). + */ +bool scx_prio_less(const struct task_struct *a, const struct task_struct *b, + bool in_fi) +{ + struct scx_sched *sch = scx_root; + + /* + * The const qualifiers are dropped from task_struct pointers when + * calling ops.core_sched_before(). Accesses are controlled by the + * verifier. + */ + if (SCX_HAS_OP(sch, core_sched_before) && + !scx_rq_bypassing(task_rq(a))) + return SCX_CALL_OP_2TASKS_RET(sch, SCX_KF_REST, core_sched_before, + NULL, + (struct task_struct *)a, + (struct task_struct *)b); + else + return time_after64(a->scx.core_sched_at, b->scx.core_sched_at); +} +#endif /* CONFIG_SCHED_CORE */ + +static int select_task_rq_scx(struct task_struct *p, int prev_cpu, int wake_flags) +{ + struct scx_sched *sch = scx_root; + bool rq_bypass; + + /* + * sched_exec() calls with %WF_EXEC when @p is about to exec(2) as it + * can be a good migration opportunity with low cache and memory + * footprint. Returning a CPU different than @prev_cpu triggers + * immediate rq migration. However, for SCX, as the current rq + * association doesn't dictate where the task is going to run, this + * doesn't fit well. If necessary, we can later add a dedicated method + * which can decide to preempt self to force it through the regular + * scheduling path. + */ + if (unlikely(wake_flags & WF_EXEC)) + return prev_cpu; + + rq_bypass = scx_rq_bypassing(task_rq(p)); + if (likely(SCX_HAS_OP(sch, select_cpu)) && !rq_bypass) { + s32 cpu; + struct task_struct **ddsp_taskp; + + ddsp_taskp = this_cpu_ptr(&direct_dispatch_task); + WARN_ON_ONCE(*ddsp_taskp); + *ddsp_taskp = p; + + cpu = SCX_CALL_OP_TASK_RET(sch, + SCX_KF_ENQUEUE | SCX_KF_SELECT_CPU, + select_cpu, NULL, p, prev_cpu, + wake_flags); + p->scx.selected_cpu = cpu; + *ddsp_taskp = NULL; + if (ops_cpu_valid(sch, cpu, "from ops.select_cpu()")) + return cpu; + else + return prev_cpu; + } else { + s32 cpu; + + cpu = scx_select_cpu_dfl(p, prev_cpu, wake_flags, NULL, 0); + if (cpu >= 0) { + refill_task_slice_dfl(sch, p); + p->scx.ddsp_dsq_id = SCX_DSQ_LOCAL; + } else { + cpu = prev_cpu; + } + p->scx.selected_cpu = cpu; + + if (rq_bypass) + __scx_add_event(sch, SCX_EV_BYPASS_DISPATCH, 1); + return cpu; + } +} + +static void task_woken_scx(struct rq *rq, struct task_struct *p) +{ + run_deferred(rq); +} + +static void set_cpus_allowed_scx(struct task_struct *p, + struct affinity_context *ac) +{ + struct scx_sched *sch = scx_root; + + set_cpus_allowed_common(p, ac); + + /* + * The effective cpumask is stored in @p->cpus_ptr which may temporarily + * differ from the configured one in @p->cpus_mask. Always tell the bpf + * scheduler the effective one. + * + * Fine-grained memory write control is enforced by BPF making the const + * designation pointless. Cast it away when calling the operation. + */ + if (SCX_HAS_OP(sch, set_cpumask)) + SCX_CALL_OP_TASK(sch, SCX_KF_REST, set_cpumask, NULL, + p, (struct cpumask *)p->cpus_ptr); +} + +static void handle_hotplug(struct rq *rq, bool online) +{ + struct scx_sched *sch = scx_root; + int cpu = cpu_of(rq); + + atomic_long_inc(&scx_hotplug_seq); + + /* + * scx_root updates are protected by cpus_read_lock() and will stay + * stable here. Note that we can't depend on scx_enabled() test as the + * hotplug ops need to be enabled before __scx_enabled is set. + */ + if (unlikely(!sch)) + return; + + if (scx_enabled()) + scx_idle_update_selcpu_topology(&sch->ops); + + if (online && SCX_HAS_OP(sch, cpu_online)) + SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cpu_online, NULL, cpu); + else if (!online && SCX_HAS_OP(sch, cpu_offline)) + SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cpu_offline, NULL, cpu); + else + scx_exit(sch, SCX_EXIT_UNREG_KERN, + SCX_ECODE_ACT_RESTART | SCX_ECODE_RSN_HOTPLUG, + "cpu %d going %s, exiting scheduler", cpu, + online ? "online" : "offline"); +} + +void scx_rq_activate(struct rq *rq) +{ + handle_hotplug(rq, true); +} + +void scx_rq_deactivate(struct rq *rq) +{ + handle_hotplug(rq, false); +} + +static void rq_online_scx(struct rq *rq) +{ + rq->scx.flags |= SCX_RQ_ONLINE; +} + +static void rq_offline_scx(struct rq *rq) +{ + rq->scx.flags &= ~SCX_RQ_ONLINE; +} + + +static bool check_rq_for_timeouts(struct rq *rq) +{ + struct scx_sched *sch; + struct task_struct *p; + struct rq_flags rf; + bool timed_out = false; + + rq_lock_irqsave(rq, &rf); + sch = rcu_dereference_bh(scx_root); + if (unlikely(!sch)) + goto out_unlock; + + list_for_each_entry(p, &rq->scx.runnable_list, scx.runnable_node) { + unsigned long last_runnable = p->scx.runnable_at; + + if (unlikely(time_after(jiffies, + last_runnable + scx_watchdog_timeout))) { + u32 dur_ms = jiffies_to_msecs(jiffies - last_runnable); + + scx_exit(sch, SCX_EXIT_ERROR_STALL, 0, + "%s[%d] failed to run for %u.%03us", + p->comm, p->pid, dur_ms / 1000, dur_ms % 1000); + timed_out = true; + break; + } + } +out_unlock: + rq_unlock_irqrestore(rq, &rf); + return timed_out; +} + +static void scx_watchdog_workfn(struct work_struct *work) +{ + int cpu; + + WRITE_ONCE(scx_watchdog_timestamp, jiffies); + + for_each_online_cpu(cpu) { + if (unlikely(check_rq_for_timeouts(cpu_rq(cpu)))) + break; + + cond_resched(); + } + queue_delayed_work(system_unbound_wq, to_delayed_work(work), + scx_watchdog_timeout / 2); +} + +void scx_tick(struct rq *rq) +{ + struct scx_sched *sch; + unsigned long last_check; + + if (!scx_enabled()) + return; + + sch = rcu_dereference_bh(scx_root); + if (unlikely(!sch)) + return; + + last_check = READ_ONCE(scx_watchdog_timestamp); + if (unlikely(time_after(jiffies, + last_check + READ_ONCE(scx_watchdog_timeout)))) { + u32 dur_ms = jiffies_to_msecs(jiffies - last_check); + + scx_exit(sch, SCX_EXIT_ERROR_STALL, 0, + "watchdog failed to check in for %u.%03us", + dur_ms / 1000, dur_ms % 1000); + } + + update_other_load_avgs(rq); +} + +static void task_tick_scx(struct rq *rq, struct task_struct *curr, int queued) +{ + struct scx_sched *sch = scx_root; + + update_curr_scx(rq); + + /* + * While disabling, always resched and refresh core-sched timestamp as + * we can't trust the slice management or ops.core_sched_before(). + */ + if (scx_rq_bypassing(rq)) { + curr->scx.slice = 0; + touch_core_sched(rq, curr); + } else if (SCX_HAS_OP(sch, tick)) { + SCX_CALL_OP_TASK(sch, SCX_KF_REST, tick, rq, curr); + } + + if (!curr->scx.slice) + resched_curr(rq); +} + +#ifdef CONFIG_EXT_GROUP_SCHED +static struct cgroup *tg_cgrp(struct task_group *tg) +{ + /* + * If CGROUP_SCHED is disabled, @tg is NULL. If @tg is an autogroup, + * @tg->css.cgroup is NULL. In both cases, @tg can be treated as the + * root cgroup. + */ + if (tg && tg->css.cgroup) + return tg->css.cgroup; + else + return &cgrp_dfl_root.cgrp; +} + +#define SCX_INIT_TASK_ARGS_CGROUP(tg) .cgroup = tg_cgrp(tg), + +#else /* CONFIG_EXT_GROUP_SCHED */ + +#define SCX_INIT_TASK_ARGS_CGROUP(tg) + +#endif /* CONFIG_EXT_GROUP_SCHED */ + +static enum scx_task_state scx_get_task_state(const struct task_struct *p) +{ + return (p->scx.flags & SCX_TASK_STATE_MASK) >> SCX_TASK_STATE_SHIFT; +} + +static void scx_set_task_state(struct task_struct *p, enum scx_task_state state) +{ + enum scx_task_state prev_state = scx_get_task_state(p); + bool warn = false; + + BUILD_BUG_ON(SCX_TASK_NR_STATES > (1 << SCX_TASK_STATE_BITS)); + + switch (state) { + case SCX_TASK_NONE: + break; + case SCX_TASK_INIT: + warn = prev_state != SCX_TASK_NONE; + break; + case SCX_TASK_READY: + warn = prev_state == SCX_TASK_NONE; + break; + case SCX_TASK_ENABLED: + warn = prev_state != SCX_TASK_READY; + break; + default: + warn = true; + return; + } + + WARN_ONCE(warn, "sched_ext: Invalid task state transition %d -> %d for %s[%d]", + prev_state, state, p->comm, p->pid); + + p->scx.flags &= ~SCX_TASK_STATE_MASK; + p->scx.flags |= state << SCX_TASK_STATE_SHIFT; +} + +static int scx_init_task(struct task_struct *p, struct task_group *tg, bool fork) +{ + struct scx_sched *sch = scx_root; + int ret; + + p->scx.disallow = false; + + if (SCX_HAS_OP(sch, init_task)) { + struct scx_init_task_args args = { + SCX_INIT_TASK_ARGS_CGROUP(tg) + .fork = fork, + }; + + ret = SCX_CALL_OP_RET(sch, SCX_KF_UNLOCKED, init_task, NULL, + p, &args); + if (unlikely(ret)) { + ret = ops_sanitize_err(sch, "init_task", ret); + return ret; + } + } + + scx_set_task_state(p, SCX_TASK_INIT); + + if (p->scx.disallow) { + if (!fork) { + struct rq *rq; + struct rq_flags rf; + + rq = task_rq_lock(p, &rf); + + /* + * We're in the load path and @p->policy will be applied + * right after. Reverting @p->policy here and rejecting + * %SCHED_EXT transitions from scx_check_setscheduler() + * guarantees that if ops.init_task() sets @p->disallow, + * @p can never be in SCX. + */ + if (p->policy == SCHED_EXT) { + p->policy = SCHED_NORMAL; + atomic_long_inc(&scx_nr_rejected); + } + + task_rq_unlock(rq, p, &rf); + } else if (p->policy == SCHED_EXT) { + scx_error(sch, "ops.init_task() set task->scx.disallow for %s[%d] during fork", + p->comm, p->pid); + } + } + + p->scx.flags |= SCX_TASK_RESET_RUNNABLE_AT; + return 0; +} + +static void scx_enable_task(struct task_struct *p) +{ + struct scx_sched *sch = scx_root; + struct rq *rq = task_rq(p); + u32 weight; + + lockdep_assert_rq_held(rq); + + /* + * Set the weight before calling ops.enable() so that the scheduler + * doesn't see a stale value if they inspect the task struct. + */ + if (task_has_idle_policy(p)) + weight = WEIGHT_IDLEPRIO; + else + weight = sched_prio_to_weight[p->static_prio - MAX_RT_PRIO]; + + p->scx.weight = sched_weight_to_cgroup(weight); + + if (SCX_HAS_OP(sch, enable)) + SCX_CALL_OP_TASK(sch, SCX_KF_REST, enable, rq, p); + scx_set_task_state(p, SCX_TASK_ENABLED); + + if (SCX_HAS_OP(sch, set_weight)) + SCX_CALL_OP_TASK(sch, SCX_KF_REST, set_weight, rq, + p, p->scx.weight); +} + +static void scx_disable_task(struct task_struct *p) +{ + struct scx_sched *sch = scx_root; + struct rq *rq = task_rq(p); + + lockdep_assert_rq_held(rq); + WARN_ON_ONCE(scx_get_task_state(p) != SCX_TASK_ENABLED); + + if (SCX_HAS_OP(sch, disable)) + SCX_CALL_OP_TASK(sch, SCX_KF_REST, disable, rq, p); + scx_set_task_state(p, SCX_TASK_READY); +} + +static void scx_exit_task(struct task_struct *p) +{ + struct scx_sched *sch = scx_root; + struct scx_exit_task_args args = { + .cancelled = false, + }; + + lockdep_assert_rq_held(task_rq(p)); + + switch (scx_get_task_state(p)) { + case SCX_TASK_NONE: + return; + case SCX_TASK_INIT: + args.cancelled = true; + break; + case SCX_TASK_READY: + break; + case SCX_TASK_ENABLED: + scx_disable_task(p); + break; + default: + WARN_ON_ONCE(true); + return; + } + + if (SCX_HAS_OP(sch, exit_task)) + SCX_CALL_OP_TASK(sch, SCX_KF_REST, exit_task, task_rq(p), + p, &args); + scx_set_task_state(p, SCX_TASK_NONE); +} + +void init_scx_entity(struct sched_ext_entity *scx) +{ + memset(scx, 0, sizeof(*scx)); + INIT_LIST_HEAD(&scx->dsq_list.node); + RB_CLEAR_NODE(&scx->dsq_priq); + scx->sticky_cpu = -1; + scx->holding_cpu = -1; + INIT_LIST_HEAD(&scx->runnable_node); + scx->runnable_at = jiffies; + scx->ddsp_dsq_id = SCX_DSQ_INVALID; + scx->slice = READ_ONCE(scx_slice_dfl); +} + +void scx_pre_fork(struct task_struct *p) +{ + /* + * BPF scheduler enable/disable paths want to be able to iterate and + * update all tasks which can become complex when racing forks. As + * enable/disable are very cold paths, let's use a percpu_rwsem to + * exclude forks. + */ + percpu_down_read(&scx_fork_rwsem); +} + +int scx_fork(struct task_struct *p) +{ + percpu_rwsem_assert_held(&scx_fork_rwsem); + + if (scx_init_task_enabled) + return scx_init_task(p, task_group(p), true); + else + return 0; +} + +void scx_post_fork(struct task_struct *p) +{ + if (scx_init_task_enabled) { + scx_set_task_state(p, SCX_TASK_READY); + + /* + * Enable the task immediately if it's running on sched_ext. + * Otherwise, it'll be enabled in switching_to_scx() if and + * when it's ever configured to run with a SCHED_EXT policy. + */ + if (p->sched_class == &ext_sched_class) { + struct rq_flags rf; + struct rq *rq; + + rq = task_rq_lock(p, &rf); + scx_enable_task(p); + task_rq_unlock(rq, p, &rf); + } + } + + raw_spin_lock_irq(&scx_tasks_lock); + list_add_tail(&p->scx.tasks_node, &scx_tasks); + raw_spin_unlock_irq(&scx_tasks_lock); + + percpu_up_read(&scx_fork_rwsem); +} + +void scx_cancel_fork(struct task_struct *p) +{ + if (scx_enabled()) { + struct rq *rq; + struct rq_flags rf; + + rq = task_rq_lock(p, &rf); + WARN_ON_ONCE(scx_get_task_state(p) >= SCX_TASK_READY); + scx_exit_task(p); + task_rq_unlock(rq, p, &rf); + } + + percpu_up_read(&scx_fork_rwsem); +} + +void sched_ext_dead(struct task_struct *p) +{ + unsigned long flags; + + raw_spin_lock_irqsave(&scx_tasks_lock, flags); + list_del_init(&p->scx.tasks_node); + raw_spin_unlock_irqrestore(&scx_tasks_lock, flags); + + /* + * @p is off scx_tasks and wholly ours. scx_enable()'s READY -> ENABLED + * transitions can't race us. Disable ops for @p. + */ + if (scx_get_task_state(p) != SCX_TASK_NONE) { + struct rq_flags rf; + struct rq *rq; + + rq = task_rq_lock(p, &rf); + scx_exit_task(p); + task_rq_unlock(rq, p, &rf); + } +} + +static void reweight_task_scx(struct rq *rq, struct task_struct *p, + const struct load_weight *lw) +{ + struct scx_sched *sch = scx_root; + + lockdep_assert_rq_held(task_rq(p)); + + p->scx.weight = sched_weight_to_cgroup(scale_load_down(lw->weight)); + if (SCX_HAS_OP(sch, set_weight)) + SCX_CALL_OP_TASK(sch, SCX_KF_REST, set_weight, rq, + p, p->scx.weight); +} + +static void prio_changed_scx(struct rq *rq, struct task_struct *p, u64 oldprio) +{ +} + +static void switching_to_scx(struct rq *rq, struct task_struct *p) +{ + struct scx_sched *sch = scx_root; + + scx_enable_task(p); + + /* + * set_cpus_allowed_scx() is not called while @p is associated with a + * different scheduler class. Keep the BPF scheduler up-to-date. + */ + if (SCX_HAS_OP(sch, set_cpumask)) + SCX_CALL_OP_TASK(sch, SCX_KF_REST, set_cpumask, rq, + p, (struct cpumask *)p->cpus_ptr); +} + +static void switched_from_scx(struct rq *rq, struct task_struct *p) +{ + scx_disable_task(p); +} + +static void wakeup_preempt_scx(struct rq *rq, struct task_struct *p,int wake_flags) {} +static void switched_to_scx(struct rq *rq, struct task_struct *p) {} + +int scx_check_setscheduler(struct task_struct *p, int policy) +{ + lockdep_assert_rq_held(task_rq(p)); + + /* if disallow, reject transitioning into SCX */ + if (scx_enabled() && READ_ONCE(p->scx.disallow) && + p->policy != policy && policy == SCHED_EXT) + return -EACCES; + + return 0; +} + +#ifdef CONFIG_NO_HZ_FULL +bool scx_can_stop_tick(struct rq *rq) +{ + struct task_struct *p = rq->curr; + + if (scx_rq_bypassing(rq)) + return false; + + if (p->sched_class != &ext_sched_class) + return true; + + /* + * @rq can dispatch from different DSQs, so we can't tell whether it + * needs the tick or not by looking at nr_running. Allow stopping ticks + * iff the BPF scheduler indicated so. See set_next_task_scx(). + */ + return rq->scx.flags & SCX_RQ_CAN_STOP_TICK; +} +#endif + +#ifdef CONFIG_EXT_GROUP_SCHED + +DEFINE_STATIC_PERCPU_RWSEM(scx_cgroup_ops_rwsem); +static bool scx_cgroup_enabled; + +void scx_tg_init(struct task_group *tg) +{ + tg->scx.weight = CGROUP_WEIGHT_DFL; + tg->scx.bw_period_us = default_bw_period_us(); + tg->scx.bw_quota_us = RUNTIME_INF; + tg->scx.idle = false; +} + +int scx_tg_online(struct task_group *tg) +{ + struct scx_sched *sch = scx_root; + int ret = 0; + + WARN_ON_ONCE(tg->scx.flags & (SCX_TG_ONLINE | SCX_TG_INITED)); + + if (scx_cgroup_enabled) { + if (SCX_HAS_OP(sch, cgroup_init)) { + struct scx_cgroup_init_args args = + { .weight = tg->scx.weight, + .bw_period_us = tg->scx.bw_period_us, + .bw_quota_us = tg->scx.bw_quota_us, + .bw_burst_us = tg->scx.bw_burst_us }; + + ret = SCX_CALL_OP_RET(sch, SCX_KF_UNLOCKED, cgroup_init, + NULL, tg->css.cgroup, &args); + if (ret) + ret = ops_sanitize_err(sch, "cgroup_init", ret); + } + if (ret == 0) + tg->scx.flags |= SCX_TG_ONLINE | SCX_TG_INITED; + } else { + tg->scx.flags |= SCX_TG_ONLINE; + } + + return ret; +} + +void scx_tg_offline(struct task_group *tg) +{ + struct scx_sched *sch = scx_root; + + WARN_ON_ONCE(!(tg->scx.flags & SCX_TG_ONLINE)); + + if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_exit) && + (tg->scx.flags & SCX_TG_INITED)) + SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_exit, NULL, + tg->css.cgroup); + tg->scx.flags &= ~(SCX_TG_ONLINE | SCX_TG_INITED); +} + +int scx_cgroup_can_attach(struct cgroup_taskset *tset) +{ + struct scx_sched *sch = scx_root; + struct cgroup_subsys_state *css; + struct task_struct *p; + int ret; + + if (!scx_cgroup_enabled) + return 0; + + cgroup_taskset_for_each(p, css, tset) { + struct cgroup *from = tg_cgrp(task_group(p)); + struct cgroup *to = tg_cgrp(css_tg(css)); + + WARN_ON_ONCE(p->scx.cgrp_moving_from); + + /* + * sched_move_task() omits identity migrations. Let's match the + * behavior so that ops.cgroup_prep_move() and ops.cgroup_move() + * always match one-to-one. + */ + if (from == to) + continue; + + if (SCX_HAS_OP(sch, cgroup_prep_move)) { + ret = SCX_CALL_OP_RET(sch, SCX_KF_UNLOCKED, + cgroup_prep_move, NULL, + p, from, css->cgroup); + if (ret) + goto err; + } + + p->scx.cgrp_moving_from = from; + } + + return 0; + +err: + cgroup_taskset_for_each(p, css, tset) { + if (SCX_HAS_OP(sch, cgroup_cancel_move) && + p->scx.cgrp_moving_from) + SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_cancel_move, NULL, + p, p->scx.cgrp_moving_from, css->cgroup); + p->scx.cgrp_moving_from = NULL; + } + + return ops_sanitize_err(sch, "cgroup_prep_move", ret); +} + +void scx_cgroup_move_task(struct task_struct *p) +{ + struct scx_sched *sch = scx_root; + + if (!scx_cgroup_enabled) + return; + + /* + * @p must have ops.cgroup_prep_move() called on it and thus + * cgrp_moving_from set. + */ + if (SCX_HAS_OP(sch, cgroup_move) && + !WARN_ON_ONCE(!p->scx.cgrp_moving_from)) + SCX_CALL_OP_TASK(sch, SCX_KF_UNLOCKED, cgroup_move, NULL, + p, p->scx.cgrp_moving_from, + tg_cgrp(task_group(p))); + p->scx.cgrp_moving_from = NULL; +} + +void scx_cgroup_cancel_attach(struct cgroup_taskset *tset) +{ + struct scx_sched *sch = scx_root; + struct cgroup_subsys_state *css; + struct task_struct *p; + + if (!scx_cgroup_enabled) + return; + + cgroup_taskset_for_each(p, css, tset) { + if (SCX_HAS_OP(sch, cgroup_cancel_move) && + p->scx.cgrp_moving_from) + SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_cancel_move, NULL, + p, p->scx.cgrp_moving_from, css->cgroup); + p->scx.cgrp_moving_from = NULL; + } +} + +void scx_group_set_weight(struct task_group *tg, unsigned long weight) +{ + struct scx_sched *sch = scx_root; + + percpu_down_read(&scx_cgroup_ops_rwsem); + + if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_set_weight) && + tg->scx.weight != weight) + SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_set_weight, NULL, + tg_cgrp(tg), weight); + + tg->scx.weight = weight; + + percpu_up_read(&scx_cgroup_ops_rwsem); +} + +void scx_group_set_idle(struct task_group *tg, bool idle) +{ + struct scx_sched *sch = scx_root; + + percpu_down_read(&scx_cgroup_ops_rwsem); + + if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_set_idle)) + SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_set_idle, NULL, + tg_cgrp(tg), idle); + + /* Update the task group's idle state */ + tg->scx.idle = idle; + + percpu_up_read(&scx_cgroup_ops_rwsem); +} + +void scx_group_set_bandwidth(struct task_group *tg, + u64 period_us, u64 quota_us, u64 burst_us) +{ + struct scx_sched *sch = scx_root; + + percpu_down_read(&scx_cgroup_ops_rwsem); + + if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_set_bandwidth) && + (tg->scx.bw_period_us != period_us || + tg->scx.bw_quota_us != quota_us || + tg->scx.bw_burst_us != burst_us)) + SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_set_bandwidth, NULL, + tg_cgrp(tg), period_us, quota_us, burst_us); + + tg->scx.bw_period_us = period_us; + tg->scx.bw_quota_us = quota_us; + tg->scx.bw_burst_us = burst_us; + + percpu_up_read(&scx_cgroup_ops_rwsem); +} + +static void scx_cgroup_lock(void) +{ + percpu_down_write(&scx_cgroup_ops_rwsem); + cgroup_lock(); +} + +static void scx_cgroup_unlock(void) +{ + cgroup_unlock(); + percpu_up_write(&scx_cgroup_ops_rwsem); +} + +#else /* CONFIG_EXT_GROUP_SCHED */ + +static void scx_cgroup_lock(void) {} +static void scx_cgroup_unlock(void) {} + +#endif /* CONFIG_EXT_GROUP_SCHED */ + +/* + * Omitted operations: + * + * - wakeup_preempt: NOOP as it isn't useful in the wakeup path because the task + * isn't tied to the CPU at that point. Preemption is implemented by resetting + * the victim task's slice to 0 and triggering reschedule on the target CPU. + * + * - migrate_task_rq: Unnecessary as task to cpu mapping is transient. + * + * - task_fork/dead: We need fork/dead notifications for all tasks regardless of + * their current sched_class. Call them directly from sched core instead. + */ +DEFINE_SCHED_CLASS(ext) = { + .queue_mask = 1, + + .enqueue_task = enqueue_task_scx, + .dequeue_task = dequeue_task_scx, + .yield_task = yield_task_scx, + .yield_to_task = yield_to_task_scx, + + .wakeup_preempt = wakeup_preempt_scx, + + .pick_task = pick_task_scx, + + .put_prev_task = put_prev_task_scx, + .set_next_task = set_next_task_scx, + + .select_task_rq = select_task_rq_scx, + .task_woken = task_woken_scx, + .set_cpus_allowed = set_cpus_allowed_scx, + + .rq_online = rq_online_scx, + .rq_offline = rq_offline_scx, + + .task_tick = task_tick_scx, + + .switching_to = switching_to_scx, + .switched_from = switched_from_scx, + .switched_to = switched_to_scx, + .reweight_task = reweight_task_scx, + .prio_changed = prio_changed_scx, + + .update_curr = update_curr_scx, + +#ifdef CONFIG_UCLAMP_TASK + .uclamp_enabled = 1, +#endif +}; + +static void init_dsq(struct scx_dispatch_q *dsq, u64 dsq_id) +{ + memset(dsq, 0, sizeof(*dsq)); + + raw_spin_lock_init(&dsq->lock); + INIT_LIST_HEAD(&dsq->list); + dsq->id = dsq_id; +} + +static void free_dsq_irq_workfn(struct irq_work *irq_work) +{ + struct llist_node *to_free = llist_del_all(&dsqs_to_free); + struct scx_dispatch_q *dsq, *tmp_dsq; + + llist_for_each_entry_safe(dsq, tmp_dsq, to_free, free_node) + kfree_rcu(dsq, rcu); +} + +static DEFINE_IRQ_WORK(free_dsq_irq_work, free_dsq_irq_workfn); + +static void destroy_dsq(struct scx_sched *sch, u64 dsq_id) +{ + struct scx_dispatch_q *dsq; + unsigned long flags; + + rcu_read_lock(); + + dsq = find_user_dsq(sch, dsq_id); + if (!dsq) + goto out_unlock_rcu; + + raw_spin_lock_irqsave(&dsq->lock, flags); + + if (dsq->nr) { + scx_error(sch, "attempting to destroy in-use dsq 0x%016llx (nr=%u)", + dsq->id, dsq->nr); + goto out_unlock_dsq; + } + + if (rhashtable_remove_fast(&sch->dsq_hash, &dsq->hash_node, + dsq_hash_params)) + goto out_unlock_dsq; + + /* + * Mark dead by invalidating ->id to prevent dispatch_enqueue() from + * queueing more tasks. As this function can be called from anywhere, + * freeing is bounced through an irq work to avoid nesting RCU + * operations inside scheduler locks. + */ + dsq->id = SCX_DSQ_INVALID; + llist_add(&dsq->free_node, &dsqs_to_free); + irq_work_queue(&free_dsq_irq_work); + +out_unlock_dsq: + raw_spin_unlock_irqrestore(&dsq->lock, flags); +out_unlock_rcu: + rcu_read_unlock(); +} + +#ifdef CONFIG_EXT_GROUP_SCHED +static void scx_cgroup_exit(struct scx_sched *sch) +{ + struct cgroup_subsys_state *css; + + scx_cgroup_enabled = false; + + /* + * scx_tg_on/offline() are excluded through cgroup_lock(). If we walk + * cgroups and exit all the inited ones, all online cgroups are exited. + */ + css_for_each_descendant_post(css, &root_task_group.css) { + struct task_group *tg = css_tg(css); + + if (!(tg->scx.flags & SCX_TG_INITED)) + continue; + tg->scx.flags &= ~SCX_TG_INITED; + + if (!sch->ops.cgroup_exit) + continue; + + SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_exit, NULL, + css->cgroup); + } +} + +static int scx_cgroup_init(struct scx_sched *sch) +{ + struct cgroup_subsys_state *css; + int ret; + + /* + * scx_tg_on/offline() are excluded through cgroup_lock(). If we walk + * cgroups and init, all online cgroups are initialized. + */ + css_for_each_descendant_pre(css, &root_task_group.css) { + struct task_group *tg = css_tg(css); + struct scx_cgroup_init_args args = { + .weight = tg->scx.weight, + .bw_period_us = tg->scx.bw_period_us, + .bw_quota_us = tg->scx.bw_quota_us, + .bw_burst_us = tg->scx.bw_burst_us, + }; + + if ((tg->scx.flags & + (SCX_TG_ONLINE | SCX_TG_INITED)) != SCX_TG_ONLINE) + continue; + + if (!sch->ops.cgroup_init) { + tg->scx.flags |= SCX_TG_INITED; + continue; + } + + ret = SCX_CALL_OP_RET(sch, SCX_KF_UNLOCKED, cgroup_init, NULL, + css->cgroup, &args); + if (ret) { + css_put(css); + scx_error(sch, "ops.cgroup_init() failed (%d)", ret); + return ret; + } + tg->scx.flags |= SCX_TG_INITED; + } + + WARN_ON_ONCE(scx_cgroup_enabled); + scx_cgroup_enabled = true; + + return 0; +} + +#else +static void scx_cgroup_exit(struct scx_sched *sch) {} +static int scx_cgroup_init(struct scx_sched *sch) { return 0; } +#endif + + +/******************************************************************************** + * Sysfs interface and ops enable/disable. + */ + +#define SCX_ATTR(_name) \ + static struct kobj_attribute scx_attr_##_name = { \ + .attr = { .name = __stringify(_name), .mode = 0444 }, \ + .show = scx_attr_##_name##_show, \ + } + +static ssize_t scx_attr_state_show(struct kobject *kobj, + struct kobj_attribute *ka, char *buf) +{ + return sysfs_emit(buf, "%s\n", scx_enable_state_str[scx_enable_state()]); +} +SCX_ATTR(state); + +static ssize_t scx_attr_switch_all_show(struct kobject *kobj, + struct kobj_attribute *ka, char *buf) +{ + return sysfs_emit(buf, "%d\n", READ_ONCE(scx_switching_all)); +} +SCX_ATTR(switch_all); + +static ssize_t scx_attr_nr_rejected_show(struct kobject *kobj, + struct kobj_attribute *ka, char *buf) +{ + return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_nr_rejected)); +} +SCX_ATTR(nr_rejected); + +static ssize_t scx_attr_hotplug_seq_show(struct kobject *kobj, + struct kobj_attribute *ka, char *buf) +{ + return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_hotplug_seq)); +} +SCX_ATTR(hotplug_seq); + +static ssize_t scx_attr_enable_seq_show(struct kobject *kobj, + struct kobj_attribute *ka, char *buf) +{ + return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_enable_seq)); +} +SCX_ATTR(enable_seq); + +static struct attribute *scx_global_attrs[] = { + &scx_attr_state.attr, + &scx_attr_switch_all.attr, + &scx_attr_nr_rejected.attr, + &scx_attr_hotplug_seq.attr, + &scx_attr_enable_seq.attr, + NULL, +}; + +static const struct attribute_group scx_global_attr_group = { + .attrs = scx_global_attrs, +}; + +static void free_exit_info(struct scx_exit_info *ei); + +static void scx_sched_free_rcu_work(struct work_struct *work) +{ + struct rcu_work *rcu_work = to_rcu_work(work); + struct scx_sched *sch = container_of(rcu_work, struct scx_sched, rcu_work); + struct rhashtable_iter rht_iter; + struct scx_dispatch_q *dsq; + int node; + + irq_work_sync(&sch->error_irq_work); + kthread_stop(sch->helper->task); + + free_percpu(sch->pcpu); + + for_each_node_state(node, N_POSSIBLE) + kfree(sch->global_dsqs[node]); + kfree(sch->global_dsqs); + + rhashtable_walk_enter(&sch->dsq_hash, &rht_iter); + do { + rhashtable_walk_start(&rht_iter); + + while ((dsq = rhashtable_walk_next(&rht_iter)) && !IS_ERR(dsq)) + destroy_dsq(sch, dsq->id); + + rhashtable_walk_stop(&rht_iter); + } while (dsq == ERR_PTR(-EAGAIN)); + rhashtable_walk_exit(&rht_iter); + + rhashtable_free_and_destroy(&sch->dsq_hash, NULL, NULL); + free_exit_info(sch->exit_info); + kfree(sch); +} + +static void scx_kobj_release(struct kobject *kobj) +{ + struct scx_sched *sch = container_of(kobj, struct scx_sched, kobj); + + INIT_RCU_WORK(&sch->rcu_work, scx_sched_free_rcu_work); + queue_rcu_work(system_unbound_wq, &sch->rcu_work); +} + +static ssize_t scx_attr_ops_show(struct kobject *kobj, + struct kobj_attribute *ka, char *buf) +{ + return sysfs_emit(buf, "%s\n", scx_root->ops.name); +} +SCX_ATTR(ops); + +#define scx_attr_event_show(buf, at, events, kind) ({ \ + sysfs_emit_at(buf, at, "%s %llu\n", #kind, (events)->kind); \ +}) + +static ssize_t scx_attr_events_show(struct kobject *kobj, + struct kobj_attribute *ka, char *buf) +{ + struct scx_sched *sch = container_of(kobj, struct scx_sched, kobj); + struct scx_event_stats events; + int at = 0; + + scx_read_events(sch, &events); + at += scx_attr_event_show(buf, at, &events, SCX_EV_SELECT_CPU_FALLBACK); + at += scx_attr_event_show(buf, at, &events, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE); + at += scx_attr_event_show(buf, at, &events, SCX_EV_DISPATCH_KEEP_LAST); + at += scx_attr_event_show(buf, at, &events, SCX_EV_ENQ_SKIP_EXITING); + at += scx_attr_event_show(buf, at, &events, SCX_EV_ENQ_SKIP_MIGRATION_DISABLED); + at += scx_attr_event_show(buf, at, &events, SCX_EV_REFILL_SLICE_DFL); + at += scx_attr_event_show(buf, at, &events, SCX_EV_BYPASS_DURATION); + at += scx_attr_event_show(buf, at, &events, SCX_EV_BYPASS_DISPATCH); + at += scx_attr_event_show(buf, at, &events, SCX_EV_BYPASS_ACTIVATE); + return at; +} +SCX_ATTR(events); + +static struct attribute *scx_sched_attrs[] = { + &scx_attr_ops.attr, + &scx_attr_events.attr, + NULL, +}; +ATTRIBUTE_GROUPS(scx_sched); + +static const struct kobj_type scx_ktype = { + .release = scx_kobj_release, + .sysfs_ops = &kobj_sysfs_ops, + .default_groups = scx_sched_groups, +}; + +static int scx_uevent(const struct kobject *kobj, struct kobj_uevent_env *env) +{ + return add_uevent_var(env, "SCXOPS=%s", scx_root->ops.name); +} + +static const struct kset_uevent_ops scx_uevent_ops = { + .uevent = scx_uevent, +}; + +/* + * Used by sched_fork() and __setscheduler_prio() to pick the matching + * sched_class. dl/rt are already handled. + */ +bool task_should_scx(int policy) +{ + if (!scx_enabled() || unlikely(scx_enable_state() == SCX_DISABLING)) + return false; + if (READ_ONCE(scx_switching_all)) + return true; + return policy == SCHED_EXT; +} + +bool scx_allow_ttwu_queue(const struct task_struct *p) +{ + struct scx_sched *sch; + + if (!scx_enabled()) + return true; + + sch = rcu_dereference_sched(scx_root); + if (unlikely(!sch)) + return true; + + if (sch->ops.flags & SCX_OPS_ALLOW_QUEUED_WAKEUP) + return true; + + if (unlikely(p->sched_class != &ext_sched_class)) + return true; + + return false; +} + +/** + * handle_lockup - sched_ext common lockup handler + * @fmt: format string + * + * Called on system stall or lockup condition and initiates abort of sched_ext + * if enabled, which may resolve the reported lockup. + * + * Returns %true if sched_ext is enabled and abort was initiated, which may + * resolve the lockup. %false if sched_ext is not enabled or abort was already + * initiated by someone else. + */ +static __printf(1, 2) bool handle_lockup(const char *fmt, ...) +{ + struct scx_sched *sch; + va_list args; + bool ret; + + guard(rcu)(); + + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + return false; + + switch (scx_enable_state()) { + case SCX_ENABLING: + case SCX_ENABLED: + va_start(args, fmt); + ret = scx_verror(sch, fmt, args); + va_end(args); + return ret; + default: + return false; + } +} + +/** + * scx_rcu_cpu_stall - sched_ext RCU CPU stall handler + * + * While there are various reasons why RCU CPU stalls can occur on a system + * that may not be caused by the current BPF scheduler, try kicking out the + * current scheduler in an attempt to recover the system to a good state before + * issuing panics. + * + * Returns %true if sched_ext is enabled and abort was initiated, which may + * resolve the reported RCU stall. %false if sched_ext is not enabled or someone + * else already initiated abort. + */ +bool scx_rcu_cpu_stall(void) +{ + return handle_lockup("RCU CPU stall detected!"); +} + +/** + * scx_softlockup - sched_ext softlockup handler + * @dur_s: number of seconds of CPU stuck due to soft lockup + * + * On some multi-socket setups (e.g. 2x Intel 8480c), the BPF scheduler can + * live-lock the system by making many CPUs target the same DSQ to the point + * where soft-lockup detection triggers. This function is called from + * soft-lockup watchdog when the triggering point is close and tries to unjam + * the system and aborting the BPF scheduler. + */ +void scx_softlockup(u32 dur_s) +{ + if (!handle_lockup("soft lockup - CPU %d stuck for %us", smp_processor_id(), dur_s)) + return; + + printk_deferred(KERN_ERR "sched_ext: Soft lockup - CPU %d stuck for %us, disabling BPF scheduler\n", + smp_processor_id(), dur_s); +} + +/** + * scx_hardlockup - sched_ext hardlockup handler + * + * A poorly behaving BPF scheduler can trigger hard lockup by e.g. putting + * numerous affinitized tasks in a single queue and directing all CPUs at it. + * Try kicking out the current scheduler in an attempt to recover the system to + * a good state before taking more drastic actions. + * + * Returns %true if sched_ext is enabled and abort was initiated, which may + * resolve the reported hardlockdup. %false if sched_ext is not enabled or + * someone else already initiated abort. + */ +bool scx_hardlockup(int cpu) +{ + if (!handle_lockup("hard lockup - CPU %d", cpu)) + return false; + + printk_deferred(KERN_ERR "sched_ext: Hard lockup - CPU %d, disabling BPF scheduler\n", + cpu); + return true; +} + +static u32 bypass_lb_cpu(struct scx_sched *sch, struct rq *rq, + struct cpumask *donee_mask, struct cpumask *resched_mask, + u32 nr_donor_target, u32 nr_donee_target) +{ + struct scx_dispatch_q *donor_dsq = &rq->scx.bypass_dsq; + struct task_struct *p, *n; + struct scx_dsq_list_node cursor = INIT_DSQ_LIST_CURSOR(cursor, 0, 0); + s32 delta = READ_ONCE(donor_dsq->nr) - nr_donor_target; + u32 nr_balanced = 0, min_delta_us; + + /* + * All we want to guarantee is reasonable forward progress. No reason to + * fine tune. Assuming every task on @donor_dsq runs their full slice, + * consider offloading iff the total queued duration is over the + * threshold. + */ + min_delta_us = scx_bypass_lb_intv_us / SCX_BYPASS_LB_MIN_DELTA_DIV; + if (delta < DIV_ROUND_UP(min_delta_us, scx_slice_bypass_us)) + return 0; + + raw_spin_rq_lock_irq(rq); + raw_spin_lock(&donor_dsq->lock); + list_add(&cursor.node, &donor_dsq->list); +resume: + n = container_of(&cursor, struct task_struct, scx.dsq_list); + n = nldsq_next_task(donor_dsq, n, false); + + while ((p = n)) { + struct rq *donee_rq; + struct scx_dispatch_q *donee_dsq; + int donee; + + n = nldsq_next_task(donor_dsq, n, false); + + if (donor_dsq->nr <= nr_donor_target) + break; + + if (cpumask_empty(donee_mask)) + break; + + donee = cpumask_any_and_distribute(donee_mask, p->cpus_ptr); + if (donee >= nr_cpu_ids) + continue; + + donee_rq = cpu_rq(donee); + donee_dsq = &donee_rq->scx.bypass_dsq; + + /* + * $p's rq is not locked but $p's DSQ lock protects its + * scheduling properties making this test safe. + */ + if (!task_can_run_on_remote_rq(sch, p, donee_rq, false)) + continue; + + /* + * Moving $p from one non-local DSQ to another. The source rq + * and DSQ are already locked. Do an abbreviated dequeue and + * then perform enqueue without unlocking $donor_dsq. + * + * We don't want to drop and reacquire the lock on each + * iteration as @donor_dsq can be very long and potentially + * highly contended. Donee DSQs are less likely to be contended. + * The nested locking is safe as only this LB moves tasks + * between bypass DSQs. + */ + dispatch_dequeue_locked(p, donor_dsq); + dispatch_enqueue(sch, donee_dsq, p, SCX_ENQ_NESTED); + + /* + * $donee might have been idle and need to be woken up. No need + * to be clever. Kick every CPU that receives tasks. + */ + cpumask_set_cpu(donee, resched_mask); + + if (READ_ONCE(donee_dsq->nr) >= nr_donee_target) + cpumask_clear_cpu(donee, donee_mask); + + nr_balanced++; + if (!(nr_balanced % SCX_BYPASS_LB_BATCH) && n) { + list_move_tail(&cursor.node, &n->scx.dsq_list.node); + raw_spin_unlock(&donor_dsq->lock); + raw_spin_rq_unlock_irq(rq); + cpu_relax(); + raw_spin_rq_lock_irq(rq); + raw_spin_lock(&donor_dsq->lock); + goto resume; + } + } + + list_del_init(&cursor.node); + raw_spin_unlock(&donor_dsq->lock); + raw_spin_rq_unlock_irq(rq); + + return nr_balanced; +} + +static void bypass_lb_node(struct scx_sched *sch, int node) +{ + const struct cpumask *node_mask = cpumask_of_node(node); + struct cpumask *donee_mask = scx_bypass_lb_donee_cpumask; + struct cpumask *resched_mask = scx_bypass_lb_resched_cpumask; + u32 nr_tasks = 0, nr_cpus = 0, nr_balanced = 0; + u32 nr_target, nr_donor_target; + u32 before_min = U32_MAX, before_max = 0; + u32 after_min = U32_MAX, after_max = 0; + int cpu; + + /* count the target tasks and CPUs */ + for_each_cpu_and(cpu, cpu_online_mask, node_mask) { + u32 nr = READ_ONCE(cpu_rq(cpu)->scx.bypass_dsq.nr); + + nr_tasks += nr; + nr_cpus++; + + before_min = min(nr, before_min); + before_max = max(nr, before_max); + } + + if (!nr_cpus) + return; + + /* + * We don't want CPUs to have more than $nr_donor_target tasks and + * balancing to fill donee CPUs upto $nr_target. Once targets are + * calculated, find the donee CPUs. + */ + nr_target = DIV_ROUND_UP(nr_tasks, nr_cpus); + nr_donor_target = DIV_ROUND_UP(nr_target * SCX_BYPASS_LB_DONOR_PCT, 100); + + cpumask_clear(donee_mask); + for_each_cpu_and(cpu, cpu_online_mask, node_mask) { + if (READ_ONCE(cpu_rq(cpu)->scx.bypass_dsq.nr) < nr_target) + cpumask_set_cpu(cpu, donee_mask); + } + + /* iterate !donee CPUs and see if they should be offloaded */ + cpumask_clear(resched_mask); + for_each_cpu_and(cpu, cpu_online_mask, node_mask) { + struct rq *rq = cpu_rq(cpu); + struct scx_dispatch_q *donor_dsq = &rq->scx.bypass_dsq; + + if (cpumask_empty(donee_mask)) + break; + if (cpumask_test_cpu(cpu, donee_mask)) + continue; + if (READ_ONCE(donor_dsq->nr) <= nr_donor_target) + continue; + + nr_balanced += bypass_lb_cpu(sch, rq, donee_mask, resched_mask, + nr_donor_target, nr_target); + } + + for_each_cpu(cpu, resched_mask) { + struct rq *rq = cpu_rq(cpu); + + raw_spin_rq_lock_irq(rq); + resched_curr(rq); + raw_spin_rq_unlock_irq(rq); + } + + for_each_cpu_and(cpu, cpu_online_mask, node_mask) { + u32 nr = READ_ONCE(cpu_rq(cpu)->scx.bypass_dsq.nr); + + after_min = min(nr, after_min); + after_max = max(nr, after_max); + + } + + trace_sched_ext_bypass_lb(node, nr_cpus, nr_tasks, nr_balanced, + before_min, before_max, after_min, after_max); +} + +/* + * In bypass mode, all tasks are put on the per-CPU bypass DSQs. If the machine + * is over-saturated and the BPF scheduler skewed tasks into few CPUs, some + * bypass DSQs can be overloaded. If there are enough tasks to saturate other + * lightly loaded CPUs, such imbalance can lead to very high execution latency + * on the overloaded CPUs and thus to hung tasks and RCU stalls. To avoid such + * outcomes, a simple load balancing mechanism is implemented by the following + * timer which runs periodically while bypass mode is in effect. + */ +static void scx_bypass_lb_timerfn(struct timer_list *timer) +{ + struct scx_sched *sch; + int node; + u32 intv_us; + + sch = rcu_dereference_all(scx_root); + if (unlikely(!sch) || !READ_ONCE(scx_bypass_depth)) + return; + + for_each_node_with_cpus(node) + bypass_lb_node(sch, node); + + intv_us = READ_ONCE(scx_bypass_lb_intv_us); + if (intv_us) + mod_timer(timer, jiffies + usecs_to_jiffies(intv_us)); +} + +static DEFINE_TIMER(scx_bypass_lb_timer, scx_bypass_lb_timerfn); + +/** + * scx_bypass - [Un]bypass scx_ops and guarantee forward progress + * @bypass: true for bypass, false for unbypass + * + * Bypassing guarantees that all runnable tasks make forward progress without + * trusting the BPF scheduler. We can't grab any mutexes or rwsems as they might + * be held by tasks that the BPF scheduler is forgetting to run, which + * unfortunately also excludes toggling the static branches. + * + * Let's work around by overriding a couple ops and modifying behaviors based on + * the DISABLING state and then cycling the queued tasks through dequeue/enqueue + * to force global FIFO scheduling. + * + * - ops.select_cpu() is ignored and the default select_cpu() is used. + * + * - ops.enqueue() is ignored and tasks are queued in simple global FIFO order. + * %SCX_OPS_ENQ_LAST is also ignored. + * + * - ops.dispatch() is ignored. + * + * - balance_scx() does not set %SCX_RQ_BAL_KEEP on non-zero slice as slice + * can't be trusted. Whenever a tick triggers, the running task is rotated to + * the tail of the queue with core_sched_at touched. + * + * - pick_next_task() suppresses zero slice warning. + * + * - scx_kick_cpu() is disabled to avoid irq_work malfunction during PM + * operations. + * + * - scx_prio_less() reverts to the default core_sched_at order. + */ +static void scx_bypass(bool bypass) +{ + static DEFINE_RAW_SPINLOCK(bypass_lock); + static unsigned long bypass_timestamp; + struct scx_sched *sch; + unsigned long flags; + int cpu; + + raw_spin_lock_irqsave(&bypass_lock, flags); + sch = rcu_dereference_bh(scx_root); + + if (bypass) { + u32 intv_us; + + WRITE_ONCE(scx_bypass_depth, scx_bypass_depth + 1); + WARN_ON_ONCE(scx_bypass_depth <= 0); + if (scx_bypass_depth != 1) + goto unlock; + WRITE_ONCE(scx_slice_dfl, scx_slice_bypass_us * NSEC_PER_USEC); + bypass_timestamp = ktime_get_ns(); + if (sch) + scx_add_event(sch, SCX_EV_BYPASS_ACTIVATE, 1); + + intv_us = READ_ONCE(scx_bypass_lb_intv_us); + if (intv_us && !timer_pending(&scx_bypass_lb_timer)) { + scx_bypass_lb_timer.expires = + jiffies + usecs_to_jiffies(intv_us); + add_timer_global(&scx_bypass_lb_timer); + } + } else { + WRITE_ONCE(scx_bypass_depth, scx_bypass_depth - 1); + WARN_ON_ONCE(scx_bypass_depth < 0); + if (scx_bypass_depth != 0) + goto unlock; + WRITE_ONCE(scx_slice_dfl, SCX_SLICE_DFL); + if (sch) + scx_add_event(sch, SCX_EV_BYPASS_DURATION, + ktime_get_ns() - bypass_timestamp); + } + + /* + * No task property is changing. We just need to make sure all currently + * queued tasks are re-queued according to the new scx_rq_bypassing() + * state. As an optimization, walk each rq's runnable_list instead of + * the scx_tasks list. + * + * This function can't trust the scheduler and thus can't use + * cpus_read_lock(). Walk all possible CPUs instead of online. + */ + for_each_possible_cpu(cpu) { + struct rq *rq = cpu_rq(cpu); + struct task_struct *p, *n; + + raw_spin_rq_lock(rq); + + if (bypass) { + WARN_ON_ONCE(rq->scx.flags & SCX_RQ_BYPASSING); + rq->scx.flags |= SCX_RQ_BYPASSING; + } else { + WARN_ON_ONCE(!(rq->scx.flags & SCX_RQ_BYPASSING)); + rq->scx.flags &= ~SCX_RQ_BYPASSING; + } + + /* + * We need to guarantee that no tasks are on the BPF scheduler + * while bypassing. Either we see enabled or the enable path + * sees scx_rq_bypassing() before moving tasks to SCX. + */ + if (!scx_enabled()) { + raw_spin_rq_unlock(rq); + continue; + } + + /* + * The use of list_for_each_entry_safe_reverse() is required + * because each task is going to be removed from and added back + * to the runnable_list during iteration. Because they're added + * to the tail of the list, safe reverse iteration can still + * visit all nodes. + */ + list_for_each_entry_safe_reverse(p, n, &rq->scx.runnable_list, + scx.runnable_node) { + /* cycling deq/enq is enough, see the function comment */ + scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) { + /* nothing */ ; + } + } + + /* resched to restore ticks and idle state */ + if (cpu_online(cpu) || cpu == smp_processor_id()) + resched_curr(rq); + + raw_spin_rq_unlock(rq); + } + +unlock: + raw_spin_unlock_irqrestore(&bypass_lock, flags); +} + +static void free_exit_info(struct scx_exit_info *ei) +{ + kvfree(ei->dump); + kfree(ei->msg); + kfree(ei->bt); + kfree(ei); +} + +static struct scx_exit_info *alloc_exit_info(size_t exit_dump_len) +{ + struct scx_exit_info *ei; + + ei = kzalloc(sizeof(*ei), GFP_KERNEL); + if (!ei) + return NULL; + + ei->bt = kcalloc(SCX_EXIT_BT_LEN, sizeof(ei->bt[0]), GFP_KERNEL); + ei->msg = kzalloc(SCX_EXIT_MSG_LEN, GFP_KERNEL); + ei->dump = kvzalloc(exit_dump_len, GFP_KERNEL); + + if (!ei->bt || !ei->msg || !ei->dump) { + free_exit_info(ei); + return NULL; + } + + return ei; +} + +static const char *scx_exit_reason(enum scx_exit_kind kind) +{ + switch (kind) { + case SCX_EXIT_UNREG: + return "unregistered from user space"; + case SCX_EXIT_UNREG_BPF: + return "unregistered from BPF"; + case SCX_EXIT_UNREG_KERN: + return "unregistered from the main kernel"; + case SCX_EXIT_SYSRQ: + return "disabled by sysrq-S"; + case SCX_EXIT_ERROR: + return "runtime error"; + case SCX_EXIT_ERROR_BPF: + return "scx_bpf_error"; + case SCX_EXIT_ERROR_STALL: + return "runnable task stall"; + default: + return "<UNKNOWN>"; + } +} + +static void free_kick_syncs(void) +{ + int cpu; + + for_each_possible_cpu(cpu) { + struct scx_kick_syncs **ksyncs = per_cpu_ptr(&scx_kick_syncs, cpu); + struct scx_kick_syncs *to_free; + + to_free = rcu_replace_pointer(*ksyncs, NULL, true); + if (to_free) + kvfree_rcu(to_free, rcu); + } +} + +static void scx_disable_workfn(struct kthread_work *work) +{ + struct scx_sched *sch = container_of(work, struct scx_sched, disable_work); + struct scx_exit_info *ei = sch->exit_info; + struct scx_task_iter sti; + struct task_struct *p; + int kind, cpu; + + kind = atomic_read(&sch->exit_kind); + while (true) { + if (kind == SCX_EXIT_DONE) /* already disabled? */ + return; + WARN_ON_ONCE(kind == SCX_EXIT_NONE); + if (atomic_try_cmpxchg(&sch->exit_kind, &kind, SCX_EXIT_DONE)) + break; + } + ei->kind = kind; + ei->reason = scx_exit_reason(ei->kind); + + /* guarantee forward progress by bypassing scx_ops */ + scx_bypass(true); + WRITE_ONCE(scx_aborting, false); + + switch (scx_set_enable_state(SCX_DISABLING)) { + case SCX_DISABLING: + WARN_ONCE(true, "sched_ext: duplicate disabling instance?"); + break; + case SCX_DISABLED: + pr_warn("sched_ext: ops error detected without ops (%s)\n", + sch->exit_info->msg); + WARN_ON_ONCE(scx_set_enable_state(SCX_DISABLED) != SCX_DISABLING); + goto done; + default: + break; + } + + /* + * Here, every runnable task is guaranteed to make forward progress and + * we can safely use blocking synchronization constructs. Actually + * disable ops. + */ + mutex_lock(&scx_enable_mutex); + + static_branch_disable(&__scx_switched_all); + WRITE_ONCE(scx_switching_all, false); + + /* + * Shut down cgroup support before tasks so that the cgroup attach path + * doesn't race against scx_exit_task(). + */ + scx_cgroup_lock(); + scx_cgroup_exit(sch); + scx_cgroup_unlock(); + + /* + * The BPF scheduler is going away. All tasks including %TASK_DEAD ones + * must be switched out and exited synchronously. + */ + percpu_down_write(&scx_fork_rwsem); + + scx_init_task_enabled = false; + + scx_task_iter_start(&sti); + while ((p = scx_task_iter_next_locked(&sti))) { + unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK; + const struct sched_class *old_class = p->sched_class; + const struct sched_class *new_class = scx_setscheduler_class(p); + + update_rq_clock(task_rq(p)); + + if (old_class != new_class) + queue_flags |= DEQUEUE_CLASS; + + scoped_guard (sched_change, p, queue_flags) { + p->sched_class = new_class; + } + + scx_exit_task(p); + } + scx_task_iter_stop(&sti); + percpu_up_write(&scx_fork_rwsem); + + /* + * Invalidate all the rq clocks to prevent getting outdated + * rq clocks from a previous scx scheduler. + */ + for_each_possible_cpu(cpu) { + struct rq *rq = cpu_rq(cpu); + scx_rq_clock_invalidate(rq); + } + + /* no task is on scx, turn off all the switches and flush in-progress calls */ + static_branch_disable(&__scx_enabled); + bitmap_zero(sch->has_op, SCX_OPI_END); + scx_idle_disable(); + synchronize_rcu(); + + if (ei->kind >= SCX_EXIT_ERROR) { + pr_err("sched_ext: BPF scheduler \"%s\" disabled (%s)\n", + sch->ops.name, ei->reason); + + if (ei->msg[0] != '\0') + pr_err("sched_ext: %s: %s\n", sch->ops.name, ei->msg); +#ifdef CONFIG_STACKTRACE + stack_trace_print(ei->bt, ei->bt_len, 2); +#endif + } else { + pr_info("sched_ext: BPF scheduler \"%s\" disabled (%s)\n", + sch->ops.name, ei->reason); + } + + if (sch->ops.exit) + SCX_CALL_OP(sch, SCX_KF_UNLOCKED, exit, NULL, ei); + + cancel_delayed_work_sync(&scx_watchdog_work); + + /* + * scx_root clearing must be inside cpus_read_lock(). See + * handle_hotplug(). + */ + cpus_read_lock(); + RCU_INIT_POINTER(scx_root, NULL); + cpus_read_unlock(); + + /* + * Delete the kobject from the hierarchy synchronously. Otherwise, sysfs + * could observe an object of the same name still in the hierarchy when + * the next scheduler is loaded. + */ + kobject_del(&sch->kobj); + + free_percpu(scx_dsp_ctx); + scx_dsp_ctx = NULL; + scx_dsp_max_batch = 0; + free_kick_syncs(); + + mutex_unlock(&scx_enable_mutex); + + WARN_ON_ONCE(scx_set_enable_state(SCX_DISABLED) != SCX_DISABLING); +done: + scx_bypass(false); +} + +static bool scx_claim_exit(struct scx_sched *sch, enum scx_exit_kind kind) +{ + int none = SCX_EXIT_NONE; + + if (!atomic_try_cmpxchg(&sch->exit_kind, &none, kind)) + return false; + + /* + * Some CPUs may be trapped in the dispatch paths. Set the aborting + * flag to break potential live-lock scenarios, ensuring we can + * successfully reach scx_bypass(). + */ + WRITE_ONCE(scx_aborting, true); + return true; +} + +static void scx_disable(enum scx_exit_kind kind) +{ + struct scx_sched *sch; + + if (WARN_ON_ONCE(kind == SCX_EXIT_NONE || kind == SCX_EXIT_DONE)) + kind = SCX_EXIT_ERROR; + + rcu_read_lock(); + sch = rcu_dereference(scx_root); + if (sch) { + scx_claim_exit(sch, kind); + kthread_queue_work(sch->helper, &sch->disable_work); + } + rcu_read_unlock(); +} + +static void dump_newline(struct seq_buf *s) +{ + trace_sched_ext_dump(""); + + /* @s may be zero sized and seq_buf triggers WARN if so */ + if (s->size) + seq_buf_putc(s, '\n'); +} + +static __printf(2, 3) void dump_line(struct seq_buf *s, const char *fmt, ...) +{ + va_list args; + +#ifdef CONFIG_TRACEPOINTS + if (trace_sched_ext_dump_enabled()) { + /* protected by scx_dump_state()::dump_lock */ + static char line_buf[SCX_EXIT_MSG_LEN]; + + va_start(args, fmt); + vscnprintf(line_buf, sizeof(line_buf), fmt, args); + va_end(args); + + trace_sched_ext_dump(line_buf); + } +#endif + /* @s may be zero sized and seq_buf triggers WARN if so */ + if (s->size) { + va_start(args, fmt); + seq_buf_vprintf(s, fmt, args); + va_end(args); + + seq_buf_putc(s, '\n'); + } +} + +static void dump_stack_trace(struct seq_buf *s, const char *prefix, + const unsigned long *bt, unsigned int len) +{ + unsigned int i; + + for (i = 0; i < len; i++) + dump_line(s, "%s%pS", prefix, (void *)bt[i]); +} + +static void ops_dump_init(struct seq_buf *s, const char *prefix) +{ + struct scx_dump_data *dd = &scx_dump_data; + + lockdep_assert_irqs_disabled(); + + dd->cpu = smp_processor_id(); /* allow scx_bpf_dump() */ + dd->first = true; + dd->cursor = 0; + dd->s = s; + dd->prefix = prefix; +} + +static void ops_dump_flush(void) +{ + struct scx_dump_data *dd = &scx_dump_data; + char *line = dd->buf.line; + + if (!dd->cursor) + return; + + /* + * There's something to flush and this is the first line. Insert a blank + * line to distinguish ops dump. + */ + if (dd->first) { + dump_newline(dd->s); + dd->first = false; + } + + /* + * There may be multiple lines in $line. Scan and emit each line + * separately. + */ + while (true) { + char *end = line; + char c; + + while (*end != '\n' && *end != '\0') + end++; + + /* + * If $line overflowed, it may not have newline at the end. + * Always emit with a newline. + */ + c = *end; + *end = '\0'; + dump_line(dd->s, "%s%s", dd->prefix, line); + if (c == '\0') + break; + + /* move to the next line */ + end++; + if (*end == '\0') + break; + line = end; + } + + dd->cursor = 0; +} + +static void ops_dump_exit(void) +{ + ops_dump_flush(); + scx_dump_data.cpu = -1; +} + +static void scx_dump_task(struct seq_buf *s, struct scx_dump_ctx *dctx, + struct task_struct *p, char marker) +{ + static unsigned long bt[SCX_EXIT_BT_LEN]; + struct scx_sched *sch = scx_root; + char dsq_id_buf[19] = "(n/a)"; + unsigned long ops_state = atomic_long_read(&p->scx.ops_state); + unsigned int bt_len = 0; + + if (p->scx.dsq) + scnprintf(dsq_id_buf, sizeof(dsq_id_buf), "0x%llx", + (unsigned long long)p->scx.dsq->id); + + dump_newline(s); + dump_line(s, " %c%c %s[%d] %+ldms", + marker, task_state_to_char(p), p->comm, p->pid, + jiffies_delta_msecs(p->scx.runnable_at, dctx->at_jiffies)); + dump_line(s, " scx_state/flags=%u/0x%x dsq_flags=0x%x ops_state/qseq=%lu/%lu", + scx_get_task_state(p), p->scx.flags & ~SCX_TASK_STATE_MASK, + p->scx.dsq_flags, ops_state & SCX_OPSS_STATE_MASK, + ops_state >> SCX_OPSS_QSEQ_SHIFT); + dump_line(s, " sticky/holding_cpu=%d/%d dsq_id=%s", + p->scx.sticky_cpu, p->scx.holding_cpu, dsq_id_buf); + dump_line(s, " dsq_vtime=%llu slice=%llu weight=%u", + p->scx.dsq_vtime, p->scx.slice, p->scx.weight); + dump_line(s, " cpus=%*pb no_mig=%u", cpumask_pr_args(p->cpus_ptr), + p->migration_disabled); + + if (SCX_HAS_OP(sch, dump_task)) { + ops_dump_init(s, " "); + SCX_CALL_OP(sch, SCX_KF_REST, dump_task, NULL, dctx, p); + ops_dump_exit(); + } + +#ifdef CONFIG_STACKTRACE + bt_len = stack_trace_save_tsk(p, bt, SCX_EXIT_BT_LEN, 1); +#endif + if (bt_len) { + dump_newline(s); + dump_stack_trace(s, " ", bt, bt_len); + } +} + +static void scx_dump_state(struct scx_exit_info *ei, size_t dump_len) +{ + static DEFINE_SPINLOCK(dump_lock); + static const char trunc_marker[] = "\n\n~~~~ TRUNCATED ~~~~\n"; + struct scx_sched *sch = scx_root; + struct scx_dump_ctx dctx = { + .kind = ei->kind, + .exit_code = ei->exit_code, + .reason = ei->reason, + .at_ns = ktime_get_ns(), + .at_jiffies = jiffies, + }; + struct seq_buf s; + struct scx_event_stats events; + unsigned long flags; + char *buf; + int cpu; + + spin_lock_irqsave(&dump_lock, flags); + + seq_buf_init(&s, ei->dump, dump_len); + + if (ei->kind == SCX_EXIT_NONE) { + dump_line(&s, "Debug dump triggered by %s", ei->reason); + } else { + dump_line(&s, "%s[%d] triggered exit kind %d:", + current->comm, current->pid, ei->kind); + dump_line(&s, " %s (%s)", ei->reason, ei->msg); + dump_newline(&s); + dump_line(&s, "Backtrace:"); + dump_stack_trace(&s, " ", ei->bt, ei->bt_len); + } + + if (SCX_HAS_OP(sch, dump)) { + ops_dump_init(&s, ""); + SCX_CALL_OP(sch, SCX_KF_UNLOCKED, dump, NULL, &dctx); + ops_dump_exit(); + } + + dump_newline(&s); + dump_line(&s, "CPU states"); + dump_line(&s, "----------"); + + for_each_possible_cpu(cpu) { + struct rq *rq = cpu_rq(cpu); + struct rq_flags rf; + struct task_struct *p; + struct seq_buf ns; + size_t avail, used; + bool idle; + + rq_lock_irqsave(rq, &rf); + + idle = list_empty(&rq->scx.runnable_list) && + rq->curr->sched_class == &idle_sched_class; + + if (idle && !SCX_HAS_OP(sch, dump_cpu)) + goto next; + + /* + * We don't yet know whether ops.dump_cpu() will produce output + * and we may want to skip the default CPU dump if it doesn't. + * Use a nested seq_buf to generate the standard dump so that we + * can decide whether to commit later. + */ + avail = seq_buf_get_buf(&s, &buf); + seq_buf_init(&ns, buf, avail); + + dump_newline(&ns); + dump_line(&ns, "CPU %-4d: nr_run=%u flags=0x%x cpu_rel=%d ops_qseq=%lu ksync=%lu", + cpu, rq->scx.nr_running, rq->scx.flags, + rq->scx.cpu_released, rq->scx.ops_qseq, + rq->scx.kick_sync); + dump_line(&ns, " curr=%s[%d] class=%ps", + rq->curr->comm, rq->curr->pid, + rq->curr->sched_class); + if (!cpumask_empty(rq->scx.cpus_to_kick)) + dump_line(&ns, " cpus_to_kick : %*pb", + cpumask_pr_args(rq->scx.cpus_to_kick)); + if (!cpumask_empty(rq->scx.cpus_to_kick_if_idle)) + dump_line(&ns, " idle_to_kick : %*pb", + cpumask_pr_args(rq->scx.cpus_to_kick_if_idle)); + if (!cpumask_empty(rq->scx.cpus_to_preempt)) + dump_line(&ns, " cpus_to_preempt: %*pb", + cpumask_pr_args(rq->scx.cpus_to_preempt)); + if (!cpumask_empty(rq->scx.cpus_to_wait)) + dump_line(&ns, " cpus_to_wait : %*pb", + cpumask_pr_args(rq->scx.cpus_to_wait)); + + used = seq_buf_used(&ns); + if (SCX_HAS_OP(sch, dump_cpu)) { + ops_dump_init(&ns, " "); + SCX_CALL_OP(sch, SCX_KF_REST, dump_cpu, NULL, + &dctx, cpu, idle); + ops_dump_exit(); + } + + /* + * If idle && nothing generated by ops.dump_cpu(), there's + * nothing interesting. Skip. + */ + if (idle && used == seq_buf_used(&ns)) + goto next; + + /* + * $s may already have overflowed when $ns was created. If so, + * calling commit on it will trigger BUG. + */ + if (avail) { + seq_buf_commit(&s, seq_buf_used(&ns)); + if (seq_buf_has_overflowed(&ns)) + seq_buf_set_overflow(&s); + } + + if (rq->curr->sched_class == &ext_sched_class) + scx_dump_task(&s, &dctx, rq->curr, '*'); + + list_for_each_entry(p, &rq->scx.runnable_list, scx.runnable_node) + scx_dump_task(&s, &dctx, p, ' '); + next: + rq_unlock_irqrestore(rq, &rf); + } + + dump_newline(&s); + dump_line(&s, "Event counters"); + dump_line(&s, "--------------"); + + scx_read_events(sch, &events); + scx_dump_event(s, &events, SCX_EV_SELECT_CPU_FALLBACK); + scx_dump_event(s, &events, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE); + scx_dump_event(s, &events, SCX_EV_DISPATCH_KEEP_LAST); + scx_dump_event(s, &events, SCX_EV_ENQ_SKIP_EXITING); + scx_dump_event(s, &events, SCX_EV_ENQ_SKIP_MIGRATION_DISABLED); + scx_dump_event(s, &events, SCX_EV_REFILL_SLICE_DFL); + scx_dump_event(s, &events, SCX_EV_BYPASS_DURATION); + scx_dump_event(s, &events, SCX_EV_BYPASS_DISPATCH); + scx_dump_event(s, &events, SCX_EV_BYPASS_ACTIVATE); + + if (seq_buf_has_overflowed(&s) && dump_len >= sizeof(trunc_marker)) + memcpy(ei->dump + dump_len - sizeof(trunc_marker), + trunc_marker, sizeof(trunc_marker)); + + spin_unlock_irqrestore(&dump_lock, flags); +} + +static void scx_error_irq_workfn(struct irq_work *irq_work) +{ + struct scx_sched *sch = container_of(irq_work, struct scx_sched, error_irq_work); + struct scx_exit_info *ei = sch->exit_info; + + if (ei->kind >= SCX_EXIT_ERROR) + scx_dump_state(ei, sch->ops.exit_dump_len); + + kthread_queue_work(sch->helper, &sch->disable_work); +} + +static bool scx_vexit(struct scx_sched *sch, + enum scx_exit_kind kind, s64 exit_code, + const char *fmt, va_list args) +{ + struct scx_exit_info *ei = sch->exit_info; + + if (!scx_claim_exit(sch, kind)) + return false; + + ei->exit_code = exit_code; +#ifdef CONFIG_STACKTRACE + if (kind >= SCX_EXIT_ERROR) + ei->bt_len = stack_trace_save(ei->bt, SCX_EXIT_BT_LEN, 1); +#endif + vscnprintf(ei->msg, SCX_EXIT_MSG_LEN, fmt, args); + + /* + * Set ei->kind and ->reason for scx_dump_state(). They'll be set again + * in scx_disable_workfn(). + */ + ei->kind = kind; + ei->reason = scx_exit_reason(ei->kind); + + irq_work_queue(&sch->error_irq_work); + return true; +} + +static int alloc_kick_syncs(void) +{ + int cpu; + + /* + * Allocate per-CPU arrays sized by nr_cpu_ids. Use kvzalloc as size + * can exceed percpu allocator limits on large machines. + */ + for_each_possible_cpu(cpu) { + struct scx_kick_syncs **ksyncs = per_cpu_ptr(&scx_kick_syncs, cpu); + struct scx_kick_syncs *new_ksyncs; + + WARN_ON_ONCE(rcu_access_pointer(*ksyncs)); + + new_ksyncs = kvzalloc_node(struct_size(new_ksyncs, syncs, nr_cpu_ids), + GFP_KERNEL, cpu_to_node(cpu)); + if (!new_ksyncs) { + free_kick_syncs(); + return -ENOMEM; + } + + rcu_assign_pointer(*ksyncs, new_ksyncs); + } + + return 0; +} + +static struct scx_sched *scx_alloc_and_add_sched(struct sched_ext_ops *ops) +{ + struct scx_sched *sch; + int node, ret; + + sch = kzalloc(sizeof(*sch), GFP_KERNEL); + if (!sch) + return ERR_PTR(-ENOMEM); + + sch->exit_info = alloc_exit_info(ops->exit_dump_len); + if (!sch->exit_info) { + ret = -ENOMEM; + goto err_free_sch; + } + + ret = rhashtable_init(&sch->dsq_hash, &dsq_hash_params); + if (ret < 0) + goto err_free_ei; + + sch->global_dsqs = kcalloc(nr_node_ids, sizeof(sch->global_dsqs[0]), + GFP_KERNEL); + if (!sch->global_dsqs) { + ret = -ENOMEM; + goto err_free_hash; + } + + for_each_node_state(node, N_POSSIBLE) { + struct scx_dispatch_q *dsq; + + dsq = kzalloc_node(sizeof(*dsq), GFP_KERNEL, node); + if (!dsq) { + ret = -ENOMEM; + goto err_free_gdsqs; + } + + init_dsq(dsq, SCX_DSQ_GLOBAL); + sch->global_dsqs[node] = dsq; + } + + sch->pcpu = alloc_percpu(struct scx_sched_pcpu); + if (!sch->pcpu) + goto err_free_gdsqs; + + sch->helper = kthread_run_worker(0, "sched_ext_helper"); + if (IS_ERR(sch->helper)) { + ret = PTR_ERR(sch->helper); + goto err_free_pcpu; + } + + sched_set_fifo(sch->helper->task); + + atomic_set(&sch->exit_kind, SCX_EXIT_NONE); + init_irq_work(&sch->error_irq_work, scx_error_irq_workfn); + kthread_init_work(&sch->disable_work, scx_disable_workfn); + sch->ops = *ops; + ops->priv = sch; + + sch->kobj.kset = scx_kset; + ret = kobject_init_and_add(&sch->kobj, &scx_ktype, NULL, "root"); + if (ret < 0) + goto err_stop_helper; + + return sch; + +err_stop_helper: + kthread_stop(sch->helper->task); +err_free_pcpu: + free_percpu(sch->pcpu); +err_free_gdsqs: + for_each_node_state(node, N_POSSIBLE) + kfree(sch->global_dsqs[node]); + kfree(sch->global_dsqs); +err_free_hash: + rhashtable_free_and_destroy(&sch->dsq_hash, NULL, NULL); +err_free_ei: + free_exit_info(sch->exit_info); +err_free_sch: + kfree(sch); + return ERR_PTR(ret); +} + +static int check_hotplug_seq(struct scx_sched *sch, + const struct sched_ext_ops *ops) +{ + unsigned long long global_hotplug_seq; + + /* + * If a hotplug event has occurred between when a scheduler was + * initialized, and when we were able to attach, exit and notify user + * space about it. + */ + if (ops->hotplug_seq) { + global_hotplug_seq = atomic_long_read(&scx_hotplug_seq); + if (ops->hotplug_seq != global_hotplug_seq) { + scx_exit(sch, SCX_EXIT_UNREG_KERN, + SCX_ECODE_ACT_RESTART | SCX_ECODE_RSN_HOTPLUG, + "expected hotplug seq %llu did not match actual %llu", + ops->hotplug_seq, global_hotplug_seq); + return -EBUSY; + } + } + + return 0; +} + +static int validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops) +{ + /* + * It doesn't make sense to specify the SCX_OPS_ENQ_LAST flag if the + * ops.enqueue() callback isn't implemented. + */ + if ((ops->flags & SCX_OPS_ENQ_LAST) && !ops->enqueue) { + scx_error(sch, "SCX_OPS_ENQ_LAST requires ops.enqueue() to be implemented"); + return -EINVAL; + } + + /* + * SCX_OPS_BUILTIN_IDLE_PER_NODE requires built-in CPU idle + * selection policy to be enabled. + */ + if ((ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE) && + (ops->update_idle && !(ops->flags & SCX_OPS_KEEP_BUILTIN_IDLE))) { + scx_error(sch, "SCX_OPS_BUILTIN_IDLE_PER_NODE requires CPU idle selection enabled"); + return -EINVAL; + } + + if (ops->flags & SCX_OPS_HAS_CGROUP_WEIGHT) + pr_warn("SCX_OPS_HAS_CGROUP_WEIGHT is deprecated and a noop\n"); + + if (ops->cpu_acquire || ops->cpu_release) + pr_warn("ops->cpu_acquire/release() are deprecated, use sched_switch TP instead\n"); + + return 0; +} + +static int scx_enable(struct sched_ext_ops *ops, struct bpf_link *link) +{ + struct scx_sched *sch; + struct scx_task_iter sti; + struct task_struct *p; + unsigned long timeout; + int i, cpu, ret; + + if (!cpumask_equal(housekeeping_cpumask(HK_TYPE_DOMAIN), + cpu_possible_mask)) { + pr_err("sched_ext: Not compatible with \"isolcpus=\" domain isolation\n"); + return -EINVAL; + } + + mutex_lock(&scx_enable_mutex); + + if (scx_enable_state() != SCX_DISABLED) { + ret = -EBUSY; + goto err_unlock; + } + + ret = alloc_kick_syncs(); + if (ret) + goto err_unlock; + + sch = scx_alloc_and_add_sched(ops); + if (IS_ERR(sch)) { + ret = PTR_ERR(sch); + goto err_free_ksyncs; + } + + /* + * Transition to ENABLING and clear exit info to arm the disable path. + * Failure triggers full disabling from here on. + */ + WARN_ON_ONCE(scx_set_enable_state(SCX_ENABLING) != SCX_DISABLED); + WARN_ON_ONCE(scx_root); + if (WARN_ON_ONCE(READ_ONCE(scx_aborting))) + WRITE_ONCE(scx_aborting, false); + + atomic_long_set(&scx_nr_rejected, 0); + + for_each_possible_cpu(cpu) + cpu_rq(cpu)->scx.cpuperf_target = SCX_CPUPERF_ONE; + + /* + * Keep CPUs stable during enable so that the BPF scheduler can track + * online CPUs by watching ->on/offline_cpu() after ->init(). + */ + cpus_read_lock(); + + /* + * Make the scheduler instance visible. Must be inside cpus_read_lock(). + * See handle_hotplug(). + */ + rcu_assign_pointer(scx_root, sch); + + scx_idle_enable(ops); + + if (sch->ops.init) { + ret = SCX_CALL_OP_RET(sch, SCX_KF_UNLOCKED, init, NULL); + if (ret) { + ret = ops_sanitize_err(sch, "init", ret); + cpus_read_unlock(); + scx_error(sch, "ops.init() failed (%d)", ret); + goto err_disable; + } + sch->exit_info->flags |= SCX_EFLAG_INITIALIZED; + } + + for (i = SCX_OPI_CPU_HOTPLUG_BEGIN; i < SCX_OPI_CPU_HOTPLUG_END; i++) + if (((void (**)(void))ops)[i]) + set_bit(i, sch->has_op); + + ret = check_hotplug_seq(sch, ops); + if (ret) { + cpus_read_unlock(); + goto err_disable; + } + scx_idle_update_selcpu_topology(ops); + + cpus_read_unlock(); + + ret = validate_ops(sch, ops); + if (ret) + goto err_disable; + + WARN_ON_ONCE(scx_dsp_ctx); + scx_dsp_max_batch = ops->dispatch_max_batch ?: SCX_DSP_DFL_MAX_BATCH; + scx_dsp_ctx = __alloc_percpu(struct_size_t(struct scx_dsp_ctx, buf, + scx_dsp_max_batch), + __alignof__(struct scx_dsp_ctx)); + if (!scx_dsp_ctx) { + ret = -ENOMEM; + goto err_disable; + } + + if (ops->timeout_ms) + timeout = msecs_to_jiffies(ops->timeout_ms); + else + timeout = SCX_WATCHDOG_MAX_TIMEOUT; + + WRITE_ONCE(scx_watchdog_timeout, timeout); + WRITE_ONCE(scx_watchdog_timestamp, jiffies); + queue_delayed_work(system_unbound_wq, &scx_watchdog_work, + scx_watchdog_timeout / 2); + + /* + * Once __scx_enabled is set, %current can be switched to SCX anytime. + * This can lead to stalls as some BPF schedulers (e.g. userspace + * scheduling) may not function correctly before all tasks are switched. + * Init in bypass mode to guarantee forward progress. + */ + scx_bypass(true); + + for (i = SCX_OPI_NORMAL_BEGIN; i < SCX_OPI_NORMAL_END; i++) + if (((void (**)(void))ops)[i]) + set_bit(i, sch->has_op); + + if (sch->ops.cpu_acquire || sch->ops.cpu_release) + sch->ops.flags |= SCX_OPS_HAS_CPU_PREEMPT; + + /* + * Lock out forks, cgroup on/offlining and moves before opening the + * floodgate so that they don't wander into the operations prematurely. + */ + percpu_down_write(&scx_fork_rwsem); + + WARN_ON_ONCE(scx_init_task_enabled); + scx_init_task_enabled = true; + + /* + * Enable ops for every task. Fork is excluded by scx_fork_rwsem + * preventing new tasks from being added. No need to exclude tasks + * leaving as sched_ext_free() can handle both prepped and enabled + * tasks. Prep all tasks first and then enable them with preemption + * disabled. + * + * All cgroups should be initialized before scx_init_task() so that the + * BPF scheduler can reliably track each task's cgroup membership from + * scx_init_task(). Lock out cgroup on/offlining and task migrations + * while tasks are being initialized so that scx_cgroup_can_attach() + * never sees uninitialized tasks. + */ + scx_cgroup_lock(); + ret = scx_cgroup_init(sch); + if (ret) + goto err_disable_unlock_all; + + scx_task_iter_start(&sti); + while ((p = scx_task_iter_next_locked(&sti))) { + /* + * @p may already be dead, have lost all its usages counts and + * be waiting for RCU grace period before being freed. @p can't + * be initialized for SCX in such cases and should be ignored. + */ + if (!tryget_task_struct(p)) + continue; + + scx_task_iter_unlock(&sti); + + ret = scx_init_task(p, task_group(p), false); + if (ret) { + put_task_struct(p); + scx_task_iter_stop(&sti); + scx_error(sch, "ops.init_task() failed (%d) for %s[%d]", + ret, p->comm, p->pid); + goto err_disable_unlock_all; + } + + scx_set_task_state(p, SCX_TASK_READY); + + put_task_struct(p); + } + scx_task_iter_stop(&sti); + scx_cgroup_unlock(); + percpu_up_write(&scx_fork_rwsem); + + /* + * All tasks are READY. It's safe to turn on scx_enabled() and switch + * all eligible tasks. + */ + WRITE_ONCE(scx_switching_all, !(ops->flags & SCX_OPS_SWITCH_PARTIAL)); + static_branch_enable(&__scx_enabled); + + /* + * We're fully committed and can't fail. The task READY -> ENABLED + * transitions here are synchronized against sched_ext_free() through + * scx_tasks_lock. + */ + percpu_down_write(&scx_fork_rwsem); + scx_task_iter_start(&sti); + while ((p = scx_task_iter_next_locked(&sti))) { + unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE; + const struct sched_class *old_class = p->sched_class; + const struct sched_class *new_class = scx_setscheduler_class(p); + + if (scx_get_task_state(p) != SCX_TASK_READY) + continue; + + if (old_class != new_class) + queue_flags |= DEQUEUE_CLASS; + + scoped_guard (sched_change, p, queue_flags) { + p->scx.slice = READ_ONCE(scx_slice_dfl); + p->sched_class = new_class; + } + } + scx_task_iter_stop(&sti); + percpu_up_write(&scx_fork_rwsem); + + scx_bypass(false); + + if (!scx_tryset_enable_state(SCX_ENABLED, SCX_ENABLING)) { + WARN_ON_ONCE(atomic_read(&sch->exit_kind) == SCX_EXIT_NONE); + goto err_disable; + } + + if (!(ops->flags & SCX_OPS_SWITCH_PARTIAL)) + static_branch_enable(&__scx_switched_all); + + pr_info("sched_ext: BPF scheduler \"%s\" enabled%s\n", + sch->ops.name, scx_switched_all() ? "" : " (partial)"); + kobject_uevent(&sch->kobj, KOBJ_ADD); + mutex_unlock(&scx_enable_mutex); + + atomic_long_inc(&scx_enable_seq); + + return 0; + +err_free_ksyncs: + free_kick_syncs(); +err_unlock: + mutex_unlock(&scx_enable_mutex); + return ret; + +err_disable_unlock_all: + scx_cgroup_unlock(); + percpu_up_write(&scx_fork_rwsem); + /* we'll soon enter disable path, keep bypass on */ +err_disable: + mutex_unlock(&scx_enable_mutex); + /* + * Returning an error code here would not pass all the error information + * to userspace. Record errno using scx_error() for cases scx_error() + * wasn't already invoked and exit indicating success so that the error + * is notified through ops.exit() with all the details. + * + * Flush scx_disable_work to ensure that error is reported before init + * completion. sch's base reference will be put by bpf_scx_unreg(). + */ + scx_error(sch, "scx_enable() failed (%d)", ret); + kthread_flush_work(&sch->disable_work); + return 0; +} + + +/******************************************************************************** + * bpf_struct_ops plumbing. + */ +#include <linux/bpf_verifier.h> +#include <linux/bpf.h> +#include <linux/btf.h> + +static const struct btf_type *task_struct_type; + +static bool bpf_scx_is_valid_access(int off, int size, + enum bpf_access_type type, + const struct bpf_prog *prog, + struct bpf_insn_access_aux *info) +{ + if (type != BPF_READ) + return false; + if (off < 0 || off >= sizeof(__u64) * MAX_BPF_FUNC_ARGS) + return false; + if (off % size != 0) + return false; + + return btf_ctx_access(off, size, type, prog, info); +} + +static int bpf_scx_btf_struct_access(struct bpf_verifier_log *log, + const struct bpf_reg_state *reg, int off, + int size) +{ + const struct btf_type *t; + + t = btf_type_by_id(reg->btf, reg->btf_id); + if (t == task_struct_type) { + if (off >= offsetof(struct task_struct, scx.slice) && + off + size <= offsetofend(struct task_struct, scx.slice)) + return SCALAR_VALUE; + if (off >= offsetof(struct task_struct, scx.dsq_vtime) && + off + size <= offsetofend(struct task_struct, scx.dsq_vtime)) + return SCALAR_VALUE; + if (off >= offsetof(struct task_struct, scx.disallow) && + off + size <= offsetofend(struct task_struct, scx.disallow)) + return SCALAR_VALUE; + } + + return -EACCES; +} + +static const struct bpf_verifier_ops bpf_scx_verifier_ops = { + .get_func_proto = bpf_base_func_proto, + .is_valid_access = bpf_scx_is_valid_access, + .btf_struct_access = bpf_scx_btf_struct_access, +}; + +static int bpf_scx_init_member(const struct btf_type *t, + const struct btf_member *member, + void *kdata, const void *udata) +{ + const struct sched_ext_ops *uops = udata; + struct sched_ext_ops *ops = kdata; + u32 moff = __btf_member_bit_offset(t, member) / 8; + int ret; + + switch (moff) { + case offsetof(struct sched_ext_ops, dispatch_max_batch): + if (*(u32 *)(udata + moff) > INT_MAX) + return -E2BIG; + ops->dispatch_max_batch = *(u32 *)(udata + moff); + return 1; + case offsetof(struct sched_ext_ops, flags): + if (*(u64 *)(udata + moff) & ~SCX_OPS_ALL_FLAGS) + return -EINVAL; + ops->flags = *(u64 *)(udata + moff); + return 1; + case offsetof(struct sched_ext_ops, name): + ret = bpf_obj_name_cpy(ops->name, uops->name, + sizeof(ops->name)); + if (ret < 0) + return ret; + if (ret == 0) + return -EINVAL; + return 1; + case offsetof(struct sched_ext_ops, timeout_ms): + if (msecs_to_jiffies(*(u32 *)(udata + moff)) > + SCX_WATCHDOG_MAX_TIMEOUT) + return -E2BIG; + ops->timeout_ms = *(u32 *)(udata + moff); + return 1; + case offsetof(struct sched_ext_ops, exit_dump_len): + ops->exit_dump_len = + *(u32 *)(udata + moff) ?: SCX_EXIT_DUMP_DFL_LEN; + return 1; + case offsetof(struct sched_ext_ops, hotplug_seq): + ops->hotplug_seq = *(u64 *)(udata + moff); + return 1; + } + + return 0; +} + +static int bpf_scx_check_member(const struct btf_type *t, + const struct btf_member *member, + const struct bpf_prog *prog) +{ + u32 moff = __btf_member_bit_offset(t, member) / 8; + + switch (moff) { + case offsetof(struct sched_ext_ops, init_task): +#ifdef CONFIG_EXT_GROUP_SCHED + case offsetof(struct sched_ext_ops, cgroup_init): + case offsetof(struct sched_ext_ops, cgroup_exit): + case offsetof(struct sched_ext_ops, cgroup_prep_move): +#endif + case offsetof(struct sched_ext_ops, cpu_online): + case offsetof(struct sched_ext_ops, cpu_offline): + case offsetof(struct sched_ext_ops, init): + case offsetof(struct sched_ext_ops, exit): + break; + default: + if (prog->sleepable) + return -EINVAL; + } + + return 0; +} + +static int bpf_scx_reg(void *kdata, struct bpf_link *link) +{ + return scx_enable(kdata, link); +} + +static void bpf_scx_unreg(void *kdata, struct bpf_link *link) +{ + struct sched_ext_ops *ops = kdata; + struct scx_sched *sch = ops->priv; + + scx_disable(SCX_EXIT_UNREG); + kthread_flush_work(&sch->disable_work); + kobject_put(&sch->kobj); +} + +static int bpf_scx_init(struct btf *btf) +{ + task_struct_type = btf_type_by_id(btf, btf_tracing_ids[BTF_TRACING_TYPE_TASK]); + + return 0; +} + +static int bpf_scx_update(void *kdata, void *old_kdata, struct bpf_link *link) +{ + /* + * sched_ext does not support updating the actively-loaded BPF + * scheduler, as registering a BPF scheduler can always fail if the + * scheduler returns an error code for e.g. ops.init(), ops.init_task(), + * etc. Similarly, we can always race with unregistration happening + * elsewhere, such as with sysrq. + */ + return -EOPNOTSUPP; +} + +static int bpf_scx_validate(void *kdata) +{ + return 0; +} + +static s32 sched_ext_ops__select_cpu(struct task_struct *p, s32 prev_cpu, u64 wake_flags) { return -EINVAL; } +static void sched_ext_ops__enqueue(struct task_struct *p, u64 enq_flags) {} +static void sched_ext_ops__dequeue(struct task_struct *p, u64 enq_flags) {} +static void sched_ext_ops__dispatch(s32 prev_cpu, struct task_struct *prev__nullable) {} +static void sched_ext_ops__tick(struct task_struct *p) {} +static void sched_ext_ops__runnable(struct task_struct *p, u64 enq_flags) {} +static void sched_ext_ops__running(struct task_struct *p) {} +static void sched_ext_ops__stopping(struct task_struct *p, bool runnable) {} +static void sched_ext_ops__quiescent(struct task_struct *p, u64 deq_flags) {} +static bool sched_ext_ops__yield(struct task_struct *from, struct task_struct *to__nullable) { return false; } +static bool sched_ext_ops__core_sched_before(struct task_struct *a, struct task_struct *b) { return false; } +static void sched_ext_ops__set_weight(struct task_struct *p, u32 weight) {} +static void sched_ext_ops__set_cpumask(struct task_struct *p, const struct cpumask *mask) {} +static void sched_ext_ops__update_idle(s32 cpu, bool idle) {} +static void sched_ext_ops__cpu_acquire(s32 cpu, struct scx_cpu_acquire_args *args) {} +static void sched_ext_ops__cpu_release(s32 cpu, struct scx_cpu_release_args *args) {} +static s32 sched_ext_ops__init_task(struct task_struct *p, struct scx_init_task_args *args) { return -EINVAL; } +static void sched_ext_ops__exit_task(struct task_struct *p, struct scx_exit_task_args *args) {} +static void sched_ext_ops__enable(struct task_struct *p) {} +static void sched_ext_ops__disable(struct task_struct *p) {} +#ifdef CONFIG_EXT_GROUP_SCHED +static s32 sched_ext_ops__cgroup_init(struct cgroup *cgrp, struct scx_cgroup_init_args *args) { return -EINVAL; } +static void sched_ext_ops__cgroup_exit(struct cgroup *cgrp) {} +static s32 sched_ext_ops__cgroup_prep_move(struct task_struct *p, struct cgroup *from, struct cgroup *to) { return -EINVAL; } +static void sched_ext_ops__cgroup_move(struct task_struct *p, struct cgroup *from, struct cgroup *to) {} +static void sched_ext_ops__cgroup_cancel_move(struct task_struct *p, struct cgroup *from, struct cgroup *to) {} +static void sched_ext_ops__cgroup_set_weight(struct cgroup *cgrp, u32 weight) {} +static void sched_ext_ops__cgroup_set_bandwidth(struct cgroup *cgrp, u64 period_us, u64 quota_us, u64 burst_us) {} +static void sched_ext_ops__cgroup_set_idle(struct cgroup *cgrp, bool idle) {} +#endif +static void sched_ext_ops__cpu_online(s32 cpu) {} +static void sched_ext_ops__cpu_offline(s32 cpu) {} +static s32 sched_ext_ops__init(void) { return -EINVAL; } +static void sched_ext_ops__exit(struct scx_exit_info *info) {} +static void sched_ext_ops__dump(struct scx_dump_ctx *ctx) {} +static void sched_ext_ops__dump_cpu(struct scx_dump_ctx *ctx, s32 cpu, bool idle) {} +static void sched_ext_ops__dump_task(struct scx_dump_ctx *ctx, struct task_struct *p) {} + +static struct sched_ext_ops __bpf_ops_sched_ext_ops = { + .select_cpu = sched_ext_ops__select_cpu, + .enqueue = sched_ext_ops__enqueue, + .dequeue = sched_ext_ops__dequeue, + .dispatch = sched_ext_ops__dispatch, + .tick = sched_ext_ops__tick, + .runnable = sched_ext_ops__runnable, + .running = sched_ext_ops__running, + .stopping = sched_ext_ops__stopping, + .quiescent = sched_ext_ops__quiescent, + .yield = sched_ext_ops__yield, + .core_sched_before = sched_ext_ops__core_sched_before, + .set_weight = sched_ext_ops__set_weight, + .set_cpumask = sched_ext_ops__set_cpumask, + .update_idle = sched_ext_ops__update_idle, + .cpu_acquire = sched_ext_ops__cpu_acquire, + .cpu_release = sched_ext_ops__cpu_release, + .init_task = sched_ext_ops__init_task, + .exit_task = sched_ext_ops__exit_task, + .enable = sched_ext_ops__enable, + .disable = sched_ext_ops__disable, +#ifdef CONFIG_EXT_GROUP_SCHED + .cgroup_init = sched_ext_ops__cgroup_init, + .cgroup_exit = sched_ext_ops__cgroup_exit, + .cgroup_prep_move = sched_ext_ops__cgroup_prep_move, + .cgroup_move = sched_ext_ops__cgroup_move, + .cgroup_cancel_move = sched_ext_ops__cgroup_cancel_move, + .cgroup_set_weight = sched_ext_ops__cgroup_set_weight, + .cgroup_set_bandwidth = sched_ext_ops__cgroup_set_bandwidth, + .cgroup_set_idle = sched_ext_ops__cgroup_set_idle, +#endif + .cpu_online = sched_ext_ops__cpu_online, + .cpu_offline = sched_ext_ops__cpu_offline, + .init = sched_ext_ops__init, + .exit = sched_ext_ops__exit, + .dump = sched_ext_ops__dump, + .dump_cpu = sched_ext_ops__dump_cpu, + .dump_task = sched_ext_ops__dump_task, +}; + +static struct bpf_struct_ops bpf_sched_ext_ops = { + .verifier_ops = &bpf_scx_verifier_ops, + .reg = bpf_scx_reg, + .unreg = bpf_scx_unreg, + .check_member = bpf_scx_check_member, + .init_member = bpf_scx_init_member, + .init = bpf_scx_init, + .update = bpf_scx_update, + .validate = bpf_scx_validate, + .name = "sched_ext_ops", + .owner = THIS_MODULE, + .cfi_stubs = &__bpf_ops_sched_ext_ops +}; + + +/******************************************************************************** + * System integration and init. + */ + +static void sysrq_handle_sched_ext_reset(u8 key) +{ + scx_disable(SCX_EXIT_SYSRQ); +} + +static const struct sysrq_key_op sysrq_sched_ext_reset_op = { + .handler = sysrq_handle_sched_ext_reset, + .help_msg = "reset-sched-ext(S)", + .action_msg = "Disable sched_ext and revert all tasks to CFS", + .enable_mask = SYSRQ_ENABLE_RTNICE, +}; + +static void sysrq_handle_sched_ext_dump(u8 key) +{ + struct scx_exit_info ei = { .kind = SCX_EXIT_NONE, .reason = "SysRq-D" }; + + if (scx_enabled()) + scx_dump_state(&ei, 0); +} + +static const struct sysrq_key_op sysrq_sched_ext_dump_op = { + .handler = sysrq_handle_sched_ext_dump, + .help_msg = "dump-sched-ext(D)", + .action_msg = "Trigger sched_ext debug dump", + .enable_mask = SYSRQ_ENABLE_RTNICE, +}; + +static bool can_skip_idle_kick(struct rq *rq) +{ + lockdep_assert_rq_held(rq); + + /* + * We can skip idle kicking if @rq is going to go through at least one + * full SCX scheduling cycle before going idle. Just checking whether + * curr is not idle is insufficient because we could be racing + * balance_one() trying to pull the next task from a remote rq, which + * may fail, and @rq may become idle afterwards. + * + * The race window is small and we don't and can't guarantee that @rq is + * only kicked while idle anyway. Skip only when sure. + */ + return !is_idle_task(rq->curr) && !(rq->scx.flags & SCX_RQ_IN_BALANCE); +} + +static bool kick_one_cpu(s32 cpu, struct rq *this_rq, unsigned long *ksyncs) +{ + struct rq *rq = cpu_rq(cpu); + struct scx_rq *this_scx = &this_rq->scx; + const struct sched_class *cur_class; + bool should_wait = false; + unsigned long flags; + + raw_spin_rq_lock_irqsave(rq, flags); + cur_class = rq->curr->sched_class; + + /* + * During CPU hotplug, a CPU may depend on kicking itself to make + * forward progress. Allow kicking self regardless of online state. If + * @cpu is running a higher class task, we have no control over @cpu. + * Skip kicking. + */ + if ((cpu_online(cpu) || cpu == cpu_of(this_rq)) && + !sched_class_above(cur_class, &ext_sched_class)) { + if (cpumask_test_cpu(cpu, this_scx->cpus_to_preempt)) { + if (cur_class == &ext_sched_class) + rq->curr->scx.slice = 0; + cpumask_clear_cpu(cpu, this_scx->cpus_to_preempt); + } + + if (cpumask_test_cpu(cpu, this_scx->cpus_to_wait)) { + if (cur_class == &ext_sched_class) { + ksyncs[cpu] = rq->scx.kick_sync; + should_wait = true; + } else { + cpumask_clear_cpu(cpu, this_scx->cpus_to_wait); + } + } + + resched_curr(rq); + } else { + cpumask_clear_cpu(cpu, this_scx->cpus_to_preempt); + cpumask_clear_cpu(cpu, this_scx->cpus_to_wait); + } + + raw_spin_rq_unlock_irqrestore(rq, flags); + + return should_wait; +} + +static void kick_one_cpu_if_idle(s32 cpu, struct rq *this_rq) +{ + struct rq *rq = cpu_rq(cpu); + unsigned long flags; + + raw_spin_rq_lock_irqsave(rq, flags); + + if (!can_skip_idle_kick(rq) && + (cpu_online(cpu) || cpu == cpu_of(this_rq))) + resched_curr(rq); + + raw_spin_rq_unlock_irqrestore(rq, flags); +} + +static void kick_cpus_irq_workfn(struct irq_work *irq_work) +{ + struct rq *this_rq = this_rq(); + struct scx_rq *this_scx = &this_rq->scx; + struct scx_kick_syncs __rcu *ksyncs_pcpu = __this_cpu_read(scx_kick_syncs); + bool should_wait = false; + unsigned long *ksyncs; + s32 cpu; + + if (unlikely(!ksyncs_pcpu)) { + pr_warn_once("kick_cpus_irq_workfn() called with NULL scx_kick_syncs"); + return; + } + + ksyncs = rcu_dereference_bh(ksyncs_pcpu)->syncs; + + for_each_cpu(cpu, this_scx->cpus_to_kick) { + should_wait |= kick_one_cpu(cpu, this_rq, ksyncs); + cpumask_clear_cpu(cpu, this_scx->cpus_to_kick); + cpumask_clear_cpu(cpu, this_scx->cpus_to_kick_if_idle); + } + + for_each_cpu(cpu, this_scx->cpus_to_kick_if_idle) { + kick_one_cpu_if_idle(cpu, this_rq); + cpumask_clear_cpu(cpu, this_scx->cpus_to_kick_if_idle); + } + + if (!should_wait) + return; + + for_each_cpu(cpu, this_scx->cpus_to_wait) { + unsigned long *wait_kick_sync = &cpu_rq(cpu)->scx.kick_sync; + + /* + * Busy-wait until the task running at the time of kicking is no + * longer running. This can be used to implement e.g. core + * scheduling. + * + * smp_cond_load_acquire() pairs with store_releases in + * pick_task_scx() and put_prev_task_scx(). The former breaks + * the wait if SCX's scheduling path is entered even if the same + * task is picked subsequently. The latter is necessary to break + * the wait when $cpu is taken by a higher sched class. + */ + if (cpu != cpu_of(this_rq)) + smp_cond_load_acquire(wait_kick_sync, VAL != ksyncs[cpu]); + + cpumask_clear_cpu(cpu, this_scx->cpus_to_wait); + } +} + +/** + * print_scx_info - print out sched_ext scheduler state + * @log_lvl: the log level to use when printing + * @p: target task + * + * If a sched_ext scheduler is enabled, print the name and state of the + * scheduler. If @p is on sched_ext, print further information about the task. + * + * This function can be safely called on any task as long as the task_struct + * itself is accessible. While safe, this function isn't synchronized and may + * print out mixups or garbages of limited length. + */ +void print_scx_info(const char *log_lvl, struct task_struct *p) +{ + struct scx_sched *sch = scx_root; + enum scx_enable_state state = scx_enable_state(); + const char *all = READ_ONCE(scx_switching_all) ? "+all" : ""; + char runnable_at_buf[22] = "?"; + struct sched_class *class; + unsigned long runnable_at; + + if (state == SCX_DISABLED) + return; + + /* + * Carefully check if the task was running on sched_ext, and then + * carefully copy the time it's been runnable, and its state. + */ + if (copy_from_kernel_nofault(&class, &p->sched_class, sizeof(class)) || + class != &ext_sched_class) { + printk("%sSched_ext: %s (%s%s)", log_lvl, sch->ops.name, + scx_enable_state_str[state], all); + return; + } + + if (!copy_from_kernel_nofault(&runnable_at, &p->scx.runnable_at, + sizeof(runnable_at))) + scnprintf(runnable_at_buf, sizeof(runnable_at_buf), "%+ldms", + jiffies_delta_msecs(runnable_at, jiffies)); + + /* print everything onto one line to conserve console space */ + printk("%sSched_ext: %s (%s%s), task: runnable_at=%s", + log_lvl, sch->ops.name, scx_enable_state_str[state], all, + runnable_at_buf); +} + +static int scx_pm_handler(struct notifier_block *nb, unsigned long event, void *ptr) +{ + /* + * SCX schedulers often have userspace components which are sometimes + * involved in critial scheduling paths. PM operations involve freezing + * userspace which can lead to scheduling misbehaviors including stalls. + * Let's bypass while PM operations are in progress. + */ + switch (event) { + case PM_HIBERNATION_PREPARE: + case PM_SUSPEND_PREPARE: + case PM_RESTORE_PREPARE: + scx_bypass(true); + break; + case PM_POST_HIBERNATION: + case PM_POST_SUSPEND: + case PM_POST_RESTORE: + scx_bypass(false); + break; + } + + return NOTIFY_OK; +} + +static struct notifier_block scx_pm_notifier = { + .notifier_call = scx_pm_handler, +}; + +void __init init_sched_ext_class(void) +{ + s32 cpu, v; + + /* + * The following is to prevent the compiler from optimizing out the enum + * definitions so that BPF scheduler implementations can use them + * through the generated vmlinux.h. + */ + WRITE_ONCE(v, SCX_ENQ_WAKEUP | SCX_DEQ_SLEEP | SCX_KICK_PREEMPT | + SCX_TG_ONLINE); + + scx_idle_init_masks(); + + for_each_possible_cpu(cpu) { + struct rq *rq = cpu_rq(cpu); + int n = cpu_to_node(cpu); + + init_dsq(&rq->scx.local_dsq, SCX_DSQ_LOCAL); + init_dsq(&rq->scx.bypass_dsq, SCX_DSQ_BYPASS); + INIT_LIST_HEAD(&rq->scx.runnable_list); + INIT_LIST_HEAD(&rq->scx.ddsp_deferred_locals); + + BUG_ON(!zalloc_cpumask_var_node(&rq->scx.cpus_to_kick, GFP_KERNEL, n)); + BUG_ON(!zalloc_cpumask_var_node(&rq->scx.cpus_to_kick_if_idle, GFP_KERNEL, n)); + BUG_ON(!zalloc_cpumask_var_node(&rq->scx.cpus_to_preempt, GFP_KERNEL, n)); + BUG_ON(!zalloc_cpumask_var_node(&rq->scx.cpus_to_wait, GFP_KERNEL, n)); + rq->scx.deferred_irq_work = IRQ_WORK_INIT_HARD(deferred_irq_workfn); + rq->scx.kick_cpus_irq_work = IRQ_WORK_INIT_HARD(kick_cpus_irq_workfn); + + if (cpu_online(cpu)) + cpu_rq(cpu)->scx.flags |= SCX_RQ_ONLINE; + } + + register_sysrq_key('S', &sysrq_sched_ext_reset_op); + register_sysrq_key('D', &sysrq_sched_ext_dump_op); + INIT_DELAYED_WORK(&scx_watchdog_work, scx_watchdog_workfn); +} + + +/******************************************************************************** + * Helpers that can be called from the BPF scheduler. + */ +static bool scx_dsq_insert_preamble(struct scx_sched *sch, struct task_struct *p, + u64 enq_flags) +{ + if (!scx_kf_allowed(sch, SCX_KF_ENQUEUE | SCX_KF_DISPATCH)) + return false; + + lockdep_assert_irqs_disabled(); + + if (unlikely(!p)) { + scx_error(sch, "called with NULL task"); + return false; + } + + if (unlikely(enq_flags & __SCX_ENQ_INTERNAL_MASK)) { + scx_error(sch, "invalid enq_flags 0x%llx", enq_flags); + return false; + } + + return true; +} + +static void scx_dsq_insert_commit(struct scx_sched *sch, struct task_struct *p, + u64 dsq_id, u64 enq_flags) +{ + struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx); + struct task_struct *ddsp_task; + + ddsp_task = __this_cpu_read(direct_dispatch_task); + if (ddsp_task) { + mark_direct_dispatch(sch, ddsp_task, p, dsq_id, enq_flags); + return; + } + + if (unlikely(dspc->cursor >= scx_dsp_max_batch)) { + scx_error(sch, "dispatch buffer overflow"); + return; + } + + dspc->buf[dspc->cursor++] = (struct scx_dsp_buf_ent){ + .task = p, + .qseq = atomic_long_read(&p->scx.ops_state) & SCX_OPSS_QSEQ_MASK, + .dsq_id = dsq_id, + .enq_flags = enq_flags, + }; +} + +__bpf_kfunc_start_defs(); + +/** + * scx_bpf_dsq_insert - Insert a task into the FIFO queue of a DSQ + * @p: task_struct to insert + * @dsq_id: DSQ to insert into + * @slice: duration @p can run for in nsecs, 0 to keep the current value + * @enq_flags: SCX_ENQ_* + * + * Insert @p into the FIFO queue of the DSQ identified by @dsq_id. It is safe to + * call this function spuriously. Can be called from ops.enqueue(), + * ops.select_cpu(), and ops.dispatch(). + * + * When called from ops.select_cpu() or ops.enqueue(), it's for direct dispatch + * and @p must match the task being enqueued. + * + * When called from ops.select_cpu(), @enq_flags and @dsp_id are stored, and @p + * will be directly inserted into the corresponding dispatch queue after + * ops.select_cpu() returns. If @p is inserted into SCX_DSQ_LOCAL, it will be + * inserted into the local DSQ of the CPU returned by ops.select_cpu(). + * @enq_flags are OR'd with the enqueue flags on the enqueue path before the + * task is inserted. + * + * When called from ops.dispatch(), there are no restrictions on @p or @dsq_id + * and this function can be called upto ops.dispatch_max_batch times to insert + * multiple tasks. scx_bpf_dispatch_nr_slots() returns the number of the + * remaining slots. scx_bpf_dsq_move_to_local() flushes the batch and resets the + * counter. + * + * This function doesn't have any locking restrictions and may be called under + * BPF locks (in the future when BPF introduces more flexible locking). + * + * @p is allowed to run for @slice. The scheduling path is triggered on slice + * exhaustion. If zero, the current residual slice is maintained. If + * %SCX_SLICE_INF, @p never expires and the BPF scheduler must kick the CPU with + * scx_bpf_kick_cpu() to trigger scheduling. + * + * Returns %true on successful insertion, %false on failure. On the root + * scheduler, %false return triggers scheduler abort and the caller doesn't need + * to check the return value. + */ +__bpf_kfunc bool scx_bpf_dsq_insert___v2(struct task_struct *p, u64 dsq_id, + u64 slice, u64 enq_flags) +{ + struct scx_sched *sch; + + guard(rcu)(); + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + return false; + + if (!scx_dsq_insert_preamble(sch, p, enq_flags)) + return false; + + if (slice) + p->scx.slice = slice; + else + p->scx.slice = p->scx.slice ?: 1; + + scx_dsq_insert_commit(sch, p, dsq_id, enq_flags); + + return true; +} + +/* + * COMPAT: Will be removed in v6.23 along with the ___v2 suffix. + */ +__bpf_kfunc void scx_bpf_dsq_insert(struct task_struct *p, u64 dsq_id, + u64 slice, u64 enq_flags) +{ + scx_bpf_dsq_insert___v2(p, dsq_id, slice, enq_flags); +} + +static bool scx_dsq_insert_vtime(struct scx_sched *sch, struct task_struct *p, + u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) +{ + if (!scx_dsq_insert_preamble(sch, p, enq_flags)) + return false; + + if (slice) + p->scx.slice = slice; + else + p->scx.slice = p->scx.slice ?: 1; + + p->scx.dsq_vtime = vtime; + + scx_dsq_insert_commit(sch, p, dsq_id, enq_flags | SCX_ENQ_DSQ_PRIQ); + + return true; +} + +struct scx_bpf_dsq_insert_vtime_args { + /* @p can't be packed together as KF_RCU is not transitive */ + u64 dsq_id; + u64 slice; + u64 vtime; + u64 enq_flags; +}; + +/** + * __scx_bpf_dsq_insert_vtime - Arg-wrapped vtime DSQ insertion + * @p: task_struct to insert + * @args: struct containing the rest of the arguments + * @args->dsq_id: DSQ to insert into + * @args->slice: duration @p can run for in nsecs, 0 to keep the current value + * @args->vtime: @p's ordering inside the vtime-sorted queue of the target DSQ + * @args->enq_flags: SCX_ENQ_* + * + * Wrapper kfunc that takes arguments via struct to work around BPF's 5 argument + * limit. BPF programs should use scx_bpf_dsq_insert_vtime() which is provided + * as an inline wrapper in common.bpf.h. + * + * Insert @p into the vtime priority queue of the DSQ identified by + * @args->dsq_id. Tasks queued into the priority queue are ordered by + * @args->vtime. All other aspects are identical to scx_bpf_dsq_insert(). + * + * @args->vtime ordering is according to time_before64() which considers + * wrapping. A numerically larger vtime may indicate an earlier position in the + * ordering and vice-versa. + * + * A DSQ can only be used as a FIFO or priority queue at any given time and this + * function must not be called on a DSQ which already has one or more FIFO tasks + * queued and vice-versa. Also, the built-in DSQs (SCX_DSQ_LOCAL and + * SCX_DSQ_GLOBAL) cannot be used as priority queues. + * + * Returns %true on successful insertion, %false on failure. On the root + * scheduler, %false return triggers scheduler abort and the caller doesn't need + * to check the return value. + */ +__bpf_kfunc bool +__scx_bpf_dsq_insert_vtime(struct task_struct *p, + struct scx_bpf_dsq_insert_vtime_args *args) +{ + struct scx_sched *sch; + + guard(rcu)(); + + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + return false; + + return scx_dsq_insert_vtime(sch, p, args->dsq_id, args->slice, + args->vtime, args->enq_flags); +} + +/* + * COMPAT: Will be removed in v6.23. + */ +__bpf_kfunc void scx_bpf_dsq_insert_vtime(struct task_struct *p, u64 dsq_id, + u64 slice, u64 vtime, u64 enq_flags) +{ + struct scx_sched *sch; + + guard(rcu)(); + + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + return; + + scx_dsq_insert_vtime(sch, p, dsq_id, slice, vtime, enq_flags); +} + +__bpf_kfunc_end_defs(); + +BTF_KFUNCS_START(scx_kfunc_ids_enqueue_dispatch) +BTF_ID_FLAGS(func, scx_bpf_dsq_insert, KF_RCU) +BTF_ID_FLAGS(func, scx_bpf_dsq_insert___v2, KF_RCU) +BTF_ID_FLAGS(func, __scx_bpf_dsq_insert_vtime, KF_RCU) +BTF_ID_FLAGS(func, scx_bpf_dsq_insert_vtime, KF_RCU) +BTF_KFUNCS_END(scx_kfunc_ids_enqueue_dispatch) + +static const struct btf_kfunc_id_set scx_kfunc_set_enqueue_dispatch = { + .owner = THIS_MODULE, + .set = &scx_kfunc_ids_enqueue_dispatch, +}; + +static bool scx_dsq_move(struct bpf_iter_scx_dsq_kern *kit, + struct task_struct *p, u64 dsq_id, u64 enq_flags) +{ + struct scx_sched *sch = scx_root; + struct scx_dispatch_q *src_dsq = kit->dsq, *dst_dsq; + struct rq *this_rq, *src_rq, *locked_rq; + bool dispatched = false; + bool in_balance; + unsigned long flags; + + if (!scx_kf_allowed_if_unlocked() && + !scx_kf_allowed(sch, SCX_KF_DISPATCH)) + return false; + + /* + * If the BPF scheduler keeps calling this function repeatedly, it can + * cause similar live-lock conditions as consume_dispatch_q(). + */ + if (unlikely(READ_ONCE(scx_aborting))) + return false; + + /* + * Can be called from either ops.dispatch() locking this_rq() or any + * context where no rq lock is held. If latter, lock @p's task_rq which + * we'll likely need anyway. + */ + src_rq = task_rq(p); + + local_irq_save(flags); + this_rq = this_rq(); + in_balance = this_rq->scx.flags & SCX_RQ_IN_BALANCE; + + if (in_balance) { + if (this_rq != src_rq) { + raw_spin_rq_unlock(this_rq); + raw_spin_rq_lock(src_rq); + } + } else { + raw_spin_rq_lock(src_rq); + } + + locked_rq = src_rq; + raw_spin_lock(&src_dsq->lock); + + /* + * Did someone else get to it? @p could have already left $src_dsq, got + * re-enqueud, or be in the process of being consumed by someone else. + */ + if (unlikely(p->scx.dsq != src_dsq || + u32_before(kit->cursor.priv, p->scx.dsq_seq) || + p->scx.holding_cpu >= 0) || + WARN_ON_ONCE(src_rq != task_rq(p))) { + raw_spin_unlock(&src_dsq->lock); + goto out; + } + + /* @p is still on $src_dsq and stable, determine the destination */ + dst_dsq = find_dsq_for_dispatch(sch, this_rq, dsq_id, p); + + /* + * Apply vtime and slice updates before moving so that the new time is + * visible before inserting into $dst_dsq. @p is still on $src_dsq but + * this is safe as we're locking it. + */ + if (kit->cursor.flags & __SCX_DSQ_ITER_HAS_VTIME) + p->scx.dsq_vtime = kit->vtime; + if (kit->cursor.flags & __SCX_DSQ_ITER_HAS_SLICE) + p->scx.slice = kit->slice; + + /* execute move */ + locked_rq = move_task_between_dsqs(sch, p, enq_flags, src_dsq, dst_dsq); + dispatched = true; +out: + if (in_balance) { + if (this_rq != locked_rq) { + raw_spin_rq_unlock(locked_rq); + raw_spin_rq_lock(this_rq); + } + } else { + raw_spin_rq_unlock_irqrestore(locked_rq, flags); + } + + kit->cursor.flags &= ~(__SCX_DSQ_ITER_HAS_SLICE | + __SCX_DSQ_ITER_HAS_VTIME); + return dispatched; +} + +__bpf_kfunc_start_defs(); + +/** + * scx_bpf_dispatch_nr_slots - Return the number of remaining dispatch slots + * + * Can only be called from ops.dispatch(). + */ +__bpf_kfunc u32 scx_bpf_dispatch_nr_slots(void) +{ + struct scx_sched *sch; + + guard(rcu)(); + + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + return 0; + + if (!scx_kf_allowed(sch, SCX_KF_DISPATCH)) + return 0; + + return scx_dsp_max_batch - __this_cpu_read(scx_dsp_ctx->cursor); +} + +/** + * scx_bpf_dispatch_cancel - Cancel the latest dispatch + * + * Cancel the latest dispatch. Can be called multiple times to cancel further + * dispatches. Can only be called from ops.dispatch(). + */ +__bpf_kfunc void scx_bpf_dispatch_cancel(void) +{ + struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx); + struct scx_sched *sch; + + guard(rcu)(); + + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + return; + + if (!scx_kf_allowed(sch, SCX_KF_DISPATCH)) + return; + + if (dspc->cursor > 0) + dspc->cursor--; + else + scx_error(sch, "dispatch buffer underflow"); +} + +/** + * scx_bpf_dsq_move_to_local - move a task from a DSQ to the current CPU's local DSQ + * @dsq_id: DSQ to move task from + * + * Move a task from the non-local DSQ identified by @dsq_id to the current CPU's + * local DSQ for execution. Can only be called from ops.dispatch(). + * + * This function flushes the in-flight dispatches from scx_bpf_dsq_insert() + * before trying to move from the specified DSQ. It may also grab rq locks and + * thus can't be called under any BPF locks. + * + * Returns %true if a task has been moved, %false if there isn't any task to + * move. + */ +__bpf_kfunc bool scx_bpf_dsq_move_to_local(u64 dsq_id) +{ + struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx); + struct scx_dispatch_q *dsq; + struct scx_sched *sch; + + guard(rcu)(); + + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + return false; + + if (!scx_kf_allowed(sch, SCX_KF_DISPATCH)) + return false; + + flush_dispatch_buf(sch, dspc->rq); + + dsq = find_user_dsq(sch, dsq_id); + if (unlikely(!dsq)) { + scx_error(sch, "invalid DSQ ID 0x%016llx", dsq_id); + return false; + } + + if (consume_dispatch_q(sch, dspc->rq, dsq)) { + /* + * A successfully consumed task can be dequeued before it starts + * running while the CPU is trying to migrate other dispatched + * tasks. Bump nr_tasks to tell balance_scx() to retry on empty + * local DSQ. + */ + dspc->nr_tasks++; + return true; + } else { + return false; + } +} + +/** + * scx_bpf_dsq_move_set_slice - Override slice when moving between DSQs + * @it__iter: DSQ iterator in progress + * @slice: duration the moved task can run for in nsecs + * + * Override the slice of the next task that will be moved from @it__iter using + * scx_bpf_dsq_move[_vtime](). If this function is not called, the previous + * slice duration is kept. + */ +__bpf_kfunc void scx_bpf_dsq_move_set_slice(struct bpf_iter_scx_dsq *it__iter, + u64 slice) +{ + struct bpf_iter_scx_dsq_kern *kit = (void *)it__iter; + + kit->slice = slice; + kit->cursor.flags |= __SCX_DSQ_ITER_HAS_SLICE; +} + +/** + * scx_bpf_dsq_move_set_vtime - Override vtime when moving between DSQs + * @it__iter: DSQ iterator in progress + * @vtime: task's ordering inside the vtime-sorted queue of the target DSQ + * + * Override the vtime of the next task that will be moved from @it__iter using + * scx_bpf_dsq_move_vtime(). If this function is not called, the previous slice + * vtime is kept. If scx_bpf_dsq_move() is used to dispatch the next task, the + * override is ignored and cleared. + */ +__bpf_kfunc void scx_bpf_dsq_move_set_vtime(struct bpf_iter_scx_dsq *it__iter, + u64 vtime) +{ + struct bpf_iter_scx_dsq_kern *kit = (void *)it__iter; + + kit->vtime = vtime; + kit->cursor.flags |= __SCX_DSQ_ITER_HAS_VTIME; +} + +/** + * scx_bpf_dsq_move - Move a task from DSQ iteration to a DSQ + * @it__iter: DSQ iterator in progress + * @p: task to transfer + * @dsq_id: DSQ to move @p to + * @enq_flags: SCX_ENQ_* + * + * Transfer @p which is on the DSQ currently iterated by @it__iter to the DSQ + * specified by @dsq_id. All DSQs - local DSQs, global DSQ and user DSQs - can + * be the destination. + * + * For the transfer to be successful, @p must still be on the DSQ and have been + * queued before the DSQ iteration started. This function doesn't care whether + * @p was obtained from the DSQ iteration. @p just has to be on the DSQ and have + * been queued before the iteration started. + * + * @p's slice is kept by default. Use scx_bpf_dsq_move_set_slice() to update. + * + * Can be called from ops.dispatch() or any BPF context which doesn't hold a rq + * lock (e.g. BPF timers or SYSCALL programs). + * + * Returns %true if @p has been consumed, %false if @p had already been + * consumed, dequeued, or, for sub-scheds, @dsq_id points to a disallowed local + * DSQ. + */ +__bpf_kfunc bool scx_bpf_dsq_move(struct bpf_iter_scx_dsq *it__iter, + struct task_struct *p, u64 dsq_id, + u64 enq_flags) +{ + return scx_dsq_move((struct bpf_iter_scx_dsq_kern *)it__iter, + p, dsq_id, enq_flags); +} + +/** + * scx_bpf_dsq_move_vtime - Move a task from DSQ iteration to a PRIQ DSQ + * @it__iter: DSQ iterator in progress + * @p: task to transfer + * @dsq_id: DSQ to move @p to + * @enq_flags: SCX_ENQ_* + * + * Transfer @p which is on the DSQ currently iterated by @it__iter to the + * priority queue of the DSQ specified by @dsq_id. The destination must be a + * user DSQ as only user DSQs support priority queue. + * + * @p's slice and vtime are kept by default. Use scx_bpf_dsq_move_set_slice() + * and scx_bpf_dsq_move_set_vtime() to update. + * + * All other aspects are identical to scx_bpf_dsq_move(). See + * scx_bpf_dsq_insert_vtime() for more information on @vtime. + */ +__bpf_kfunc bool scx_bpf_dsq_move_vtime(struct bpf_iter_scx_dsq *it__iter, + struct task_struct *p, u64 dsq_id, + u64 enq_flags) +{ + return scx_dsq_move((struct bpf_iter_scx_dsq_kern *)it__iter, + p, dsq_id, enq_flags | SCX_ENQ_DSQ_PRIQ); +} + +__bpf_kfunc_end_defs(); + +BTF_KFUNCS_START(scx_kfunc_ids_dispatch) +BTF_ID_FLAGS(func, scx_bpf_dispatch_nr_slots) +BTF_ID_FLAGS(func, scx_bpf_dispatch_cancel) +BTF_ID_FLAGS(func, scx_bpf_dsq_move_to_local) +BTF_ID_FLAGS(func, scx_bpf_dsq_move_set_slice, KF_RCU) +BTF_ID_FLAGS(func, scx_bpf_dsq_move_set_vtime, KF_RCU) +BTF_ID_FLAGS(func, scx_bpf_dsq_move, KF_RCU) +BTF_ID_FLAGS(func, scx_bpf_dsq_move_vtime, KF_RCU) +BTF_KFUNCS_END(scx_kfunc_ids_dispatch) + +static const struct btf_kfunc_id_set scx_kfunc_set_dispatch = { + .owner = THIS_MODULE, + .set = &scx_kfunc_ids_dispatch, +}; + +static u32 reenq_local(struct rq *rq) +{ + LIST_HEAD(tasks); + u32 nr_enqueued = 0; + struct task_struct *p, *n; + + lockdep_assert_rq_held(rq); + + /* + * The BPF scheduler may choose to dispatch tasks back to + * @rq->scx.local_dsq. Move all candidate tasks off to a private list + * first to avoid processing the same tasks repeatedly. + */ + list_for_each_entry_safe(p, n, &rq->scx.local_dsq.list, + scx.dsq_list.node) { + /* + * If @p is being migrated, @p's current CPU may not agree with + * its allowed CPUs and the migration_cpu_stop is about to + * deactivate and re-activate @p anyway. Skip re-enqueueing. + * + * While racing sched property changes may also dequeue and + * re-enqueue a migrating task while its current CPU and allowed + * CPUs disagree, they use %ENQUEUE_RESTORE which is bypassed to + * the current local DSQ for running tasks and thus are not + * visible to the BPF scheduler. + */ + if (p->migration_pending) + continue; + + dispatch_dequeue(rq, p); + list_add_tail(&p->scx.dsq_list.node, &tasks); + } + + list_for_each_entry_safe(p, n, &tasks, scx.dsq_list.node) { + list_del_init(&p->scx.dsq_list.node); + do_enqueue_task(rq, p, SCX_ENQ_REENQ, -1); + nr_enqueued++; + } + + return nr_enqueued; +} + +__bpf_kfunc_start_defs(); + +/** + * scx_bpf_reenqueue_local - Re-enqueue tasks on a local DSQ + * + * Iterate over all of the tasks currently enqueued on the local DSQ of the + * caller's CPU, and re-enqueue them in the BPF scheduler. Returns the number of + * processed tasks. Can only be called from ops.cpu_release(). + * + * COMPAT: Will be removed in v6.23 along with the ___v2 suffix on the void + * returning variant that can be called from anywhere. + */ +__bpf_kfunc u32 scx_bpf_reenqueue_local(void) +{ + struct scx_sched *sch; + struct rq *rq; + + guard(rcu)(); + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + return 0; + + if (!scx_kf_allowed(sch, SCX_KF_CPU_RELEASE)) + return 0; + + rq = cpu_rq(smp_processor_id()); + lockdep_assert_rq_held(rq); + + return reenq_local(rq); +} + +__bpf_kfunc_end_defs(); + +BTF_KFUNCS_START(scx_kfunc_ids_cpu_release) +BTF_ID_FLAGS(func, scx_bpf_reenqueue_local) +BTF_KFUNCS_END(scx_kfunc_ids_cpu_release) + +static const struct btf_kfunc_id_set scx_kfunc_set_cpu_release = { + .owner = THIS_MODULE, + .set = &scx_kfunc_ids_cpu_release, +}; + +__bpf_kfunc_start_defs(); + +/** + * scx_bpf_create_dsq - Create a custom DSQ + * @dsq_id: DSQ to create + * @node: NUMA node to allocate from + * + * Create a custom DSQ identified by @dsq_id. Can be called from any sleepable + * scx callback, and any BPF_PROG_TYPE_SYSCALL prog. + */ +__bpf_kfunc s32 scx_bpf_create_dsq(u64 dsq_id, s32 node) +{ + struct scx_dispatch_q *dsq; + struct scx_sched *sch; + s32 ret; + + if (unlikely(node >= (int)nr_node_ids || + (node < 0 && node != NUMA_NO_NODE))) + return -EINVAL; + + if (unlikely(dsq_id & SCX_DSQ_FLAG_BUILTIN)) + return -EINVAL; + + dsq = kmalloc_node(sizeof(*dsq), GFP_KERNEL, node); + if (!dsq) + return -ENOMEM; + + init_dsq(dsq, dsq_id); + + rcu_read_lock(); + + sch = rcu_dereference(scx_root); + if (sch) + ret = rhashtable_lookup_insert_fast(&sch->dsq_hash, &dsq->hash_node, + dsq_hash_params); + else + ret = -ENODEV; + + rcu_read_unlock(); + if (ret) + kfree(dsq); + return ret; +} + +__bpf_kfunc_end_defs(); + +BTF_KFUNCS_START(scx_kfunc_ids_unlocked) +BTF_ID_FLAGS(func, scx_bpf_create_dsq, KF_SLEEPABLE) +BTF_ID_FLAGS(func, scx_bpf_dsq_move_set_slice, KF_RCU) +BTF_ID_FLAGS(func, scx_bpf_dsq_move_set_vtime, KF_RCU) +BTF_ID_FLAGS(func, scx_bpf_dsq_move, KF_RCU) +BTF_ID_FLAGS(func, scx_bpf_dsq_move_vtime, KF_RCU) +BTF_KFUNCS_END(scx_kfunc_ids_unlocked) + +static const struct btf_kfunc_id_set scx_kfunc_set_unlocked = { + .owner = THIS_MODULE, + .set = &scx_kfunc_ids_unlocked, +}; + +__bpf_kfunc_start_defs(); + +/** + * scx_bpf_task_set_slice - Set task's time slice + * @p: task of interest + * @slice: time slice to set in nsecs + * + * Set @p's time slice to @slice. Returns %true on success, %false if the + * calling scheduler doesn't have authority over @p. + */ +__bpf_kfunc bool scx_bpf_task_set_slice(struct task_struct *p, u64 slice) +{ + p->scx.slice = slice; + return true; +} + +/** + * scx_bpf_task_set_dsq_vtime - Set task's virtual time for DSQ ordering + * @p: task of interest + * @vtime: virtual time to set + * + * Set @p's virtual time to @vtime. Returns %true on success, %false if the + * calling scheduler doesn't have authority over @p. + */ +__bpf_kfunc bool scx_bpf_task_set_dsq_vtime(struct task_struct *p, u64 vtime) +{ + p->scx.dsq_vtime = vtime; + return true; +} + +static void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags) +{ + struct rq *this_rq; + unsigned long irq_flags; + + if (!ops_cpu_valid(sch, cpu, NULL)) + return; + + local_irq_save(irq_flags); + + this_rq = this_rq(); + + /* + * While bypassing for PM ops, IRQ handling may not be online which can + * lead to irq_work_queue() malfunction such as infinite busy wait for + * IRQ status update. Suppress kicking. + */ + if (scx_rq_bypassing(this_rq)) + goto out; + + /* + * Actual kicking is bounced to kick_cpus_irq_workfn() to avoid nesting + * rq locks. We can probably be smarter and avoid bouncing if called + * from ops which don't hold a rq lock. + */ + if (flags & SCX_KICK_IDLE) { + struct rq *target_rq = cpu_rq(cpu); + + if (unlikely(flags & (SCX_KICK_PREEMPT | SCX_KICK_WAIT))) + scx_error(sch, "PREEMPT/WAIT cannot be used with SCX_KICK_IDLE"); + + if (raw_spin_rq_trylock(target_rq)) { + if (can_skip_idle_kick(target_rq)) { + raw_spin_rq_unlock(target_rq); + goto out; + } + raw_spin_rq_unlock(target_rq); + } + cpumask_set_cpu(cpu, this_rq->scx.cpus_to_kick_if_idle); + } else { + cpumask_set_cpu(cpu, this_rq->scx.cpus_to_kick); + + if (flags & SCX_KICK_PREEMPT) + cpumask_set_cpu(cpu, this_rq->scx.cpus_to_preempt); + if (flags & SCX_KICK_WAIT) + cpumask_set_cpu(cpu, this_rq->scx.cpus_to_wait); + } + + irq_work_queue(&this_rq->scx.kick_cpus_irq_work); +out: + local_irq_restore(irq_flags); +} + +/** + * scx_bpf_kick_cpu - Trigger reschedule on a CPU + * @cpu: cpu to kick + * @flags: %SCX_KICK_* flags + * + * Kick @cpu into rescheduling. This can be used to wake up an idle CPU or + * trigger rescheduling on a busy CPU. This can be called from any online + * scx_ops operation and the actual kicking is performed asynchronously through + * an irq work. + */ +__bpf_kfunc void scx_bpf_kick_cpu(s32 cpu, u64 flags) +{ + struct scx_sched *sch; + + guard(rcu)(); + sch = rcu_dereference(scx_root); + if (likely(sch)) + scx_kick_cpu(sch, cpu, flags); +} + +/** + * scx_bpf_dsq_nr_queued - Return the number of queued tasks + * @dsq_id: id of the DSQ + * + * Return the number of tasks in the DSQ matching @dsq_id. If not found, + * -%ENOENT is returned. + */ +__bpf_kfunc s32 scx_bpf_dsq_nr_queued(u64 dsq_id) +{ + struct scx_sched *sch; + struct scx_dispatch_q *dsq; + s32 ret; + + preempt_disable(); + + sch = rcu_dereference_sched(scx_root); + if (unlikely(!sch)) { + ret = -ENODEV; + goto out; + } + + if (dsq_id == SCX_DSQ_LOCAL) { + ret = READ_ONCE(this_rq()->scx.local_dsq.nr); + goto out; + } else if ((dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON) { + s32 cpu = dsq_id & SCX_DSQ_LOCAL_CPU_MASK; + + if (ops_cpu_valid(sch, cpu, NULL)) { + ret = READ_ONCE(cpu_rq(cpu)->scx.local_dsq.nr); + goto out; + } + } else { + dsq = find_user_dsq(sch, dsq_id); + if (dsq) { + ret = READ_ONCE(dsq->nr); + goto out; + } + } + ret = -ENOENT; +out: + preempt_enable(); + return ret; +} + +/** + * scx_bpf_destroy_dsq - Destroy a custom DSQ + * @dsq_id: DSQ to destroy + * + * Destroy the custom DSQ identified by @dsq_id. Only DSQs created with + * scx_bpf_create_dsq() can be destroyed. The caller must ensure that the DSQ is + * empty and no further tasks are dispatched to it. Ignored if called on a DSQ + * which doesn't exist. Can be called from any online scx_ops operations. + */ +__bpf_kfunc void scx_bpf_destroy_dsq(u64 dsq_id) +{ + struct scx_sched *sch; + + rcu_read_lock(); + sch = rcu_dereference(scx_root); + if (sch) + destroy_dsq(sch, dsq_id); + rcu_read_unlock(); +} + +/** + * bpf_iter_scx_dsq_new - Create a DSQ iterator + * @it: iterator to initialize + * @dsq_id: DSQ to iterate + * @flags: %SCX_DSQ_ITER_* + * + * Initialize BPF iterator @it which can be used with bpf_for_each() to walk + * tasks in the DSQ specified by @dsq_id. Iteration using @it only includes + * tasks which are already queued when this function is invoked. + */ +__bpf_kfunc int bpf_iter_scx_dsq_new(struct bpf_iter_scx_dsq *it, u64 dsq_id, + u64 flags) +{ + struct bpf_iter_scx_dsq_kern *kit = (void *)it; + struct scx_sched *sch; + + BUILD_BUG_ON(sizeof(struct bpf_iter_scx_dsq_kern) > + sizeof(struct bpf_iter_scx_dsq)); + BUILD_BUG_ON(__alignof__(struct bpf_iter_scx_dsq_kern) != + __alignof__(struct bpf_iter_scx_dsq)); + BUILD_BUG_ON(__SCX_DSQ_ITER_ALL_FLAGS & + ((1U << __SCX_DSQ_LNODE_PRIV_SHIFT) - 1)); + + /* + * next() and destroy() will be called regardless of the return value. + * Always clear $kit->dsq. + */ + kit->dsq = NULL; + + sch = rcu_dereference_check(scx_root, rcu_read_lock_bh_held()); + if (unlikely(!sch)) + return -ENODEV; + + if (flags & ~__SCX_DSQ_ITER_USER_FLAGS) + return -EINVAL; + + kit->dsq = find_user_dsq(sch, dsq_id); + if (!kit->dsq) + return -ENOENT; + + kit->cursor = INIT_DSQ_LIST_CURSOR(kit->cursor, flags, + READ_ONCE(kit->dsq->seq)); + + return 0; +} + +/** + * bpf_iter_scx_dsq_next - Progress a DSQ iterator + * @it: iterator to progress + * + * Return the next task. See bpf_iter_scx_dsq_new(). + */ +__bpf_kfunc struct task_struct *bpf_iter_scx_dsq_next(struct bpf_iter_scx_dsq *it) +{ + struct bpf_iter_scx_dsq_kern *kit = (void *)it; + bool rev = kit->cursor.flags & SCX_DSQ_ITER_REV; + struct task_struct *p; + unsigned long flags; + + if (!kit->dsq) + return NULL; + + raw_spin_lock_irqsave(&kit->dsq->lock, flags); + + if (list_empty(&kit->cursor.node)) + p = NULL; + else + p = container_of(&kit->cursor, struct task_struct, scx.dsq_list); + + /* + * Only tasks which were queued before the iteration started are + * visible. This bounds BPF iterations and guarantees that vtime never + * jumps in the other direction while iterating. + */ + do { + p = nldsq_next_task(kit->dsq, p, rev); + } while (p && unlikely(u32_before(kit->cursor.priv, p->scx.dsq_seq))); + + if (p) { + if (rev) + list_move_tail(&kit->cursor.node, &p->scx.dsq_list.node); + else + list_move(&kit->cursor.node, &p->scx.dsq_list.node); + } else { + list_del_init(&kit->cursor.node); + } + + raw_spin_unlock_irqrestore(&kit->dsq->lock, flags); + + return p; +} + +/** + * bpf_iter_scx_dsq_destroy - Destroy a DSQ iterator + * @it: iterator to destroy + * + * Undo scx_iter_scx_dsq_new(). + */ +__bpf_kfunc void bpf_iter_scx_dsq_destroy(struct bpf_iter_scx_dsq *it) +{ + struct bpf_iter_scx_dsq_kern *kit = (void *)it; + + if (!kit->dsq) + return; + + if (!list_empty(&kit->cursor.node)) { + unsigned long flags; + + raw_spin_lock_irqsave(&kit->dsq->lock, flags); + list_del_init(&kit->cursor.node); + raw_spin_unlock_irqrestore(&kit->dsq->lock, flags); + } + kit->dsq = NULL; +} + +/** + * scx_bpf_dsq_peek - Lockless peek at the first element. + * @dsq_id: DSQ to examine. + * + * Read the first element in the DSQ. This is semantically equivalent to using + * the DSQ iterator, but is lockfree. Of course, like any lockless operation, + * this provides only a point-in-time snapshot, and the contents may change + * by the time any subsequent locking operation reads the queue. + * + * Returns the pointer, or NULL indicates an empty queue OR internal error. + */ +__bpf_kfunc struct task_struct *scx_bpf_dsq_peek(u64 dsq_id) +{ + struct scx_sched *sch; + struct scx_dispatch_q *dsq; + + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + return NULL; + + if (unlikely(dsq_id & SCX_DSQ_FLAG_BUILTIN)) { + scx_error(sch, "peek disallowed on builtin DSQ 0x%llx", dsq_id); + return NULL; + } + + dsq = find_user_dsq(sch, dsq_id); + if (unlikely(!dsq)) { + scx_error(sch, "peek on non-existent DSQ 0x%llx", dsq_id); + return NULL; + } + + return rcu_dereference(dsq->first_task); +} + +__bpf_kfunc_end_defs(); + +static s32 __bstr_format(struct scx_sched *sch, u64 *data_buf, char *line_buf, + size_t line_size, char *fmt, unsigned long long *data, + u32 data__sz) +{ + struct bpf_bprintf_data bprintf_data = { .get_bin_args = true }; + s32 ret; + + if (data__sz % 8 || data__sz > MAX_BPRINTF_VARARGS * 8 || + (data__sz && !data)) { + scx_error(sch, "invalid data=%p and data__sz=%u", (void *)data, data__sz); + return -EINVAL; + } + + ret = copy_from_kernel_nofault(data_buf, data, data__sz); + if (ret < 0) { + scx_error(sch, "failed to read data fields (%d)", ret); + return ret; + } + + ret = bpf_bprintf_prepare(fmt, UINT_MAX, data_buf, data__sz / 8, + &bprintf_data); + if (ret < 0) { + scx_error(sch, "format preparation failed (%d)", ret); + return ret; + } + + ret = bstr_printf(line_buf, line_size, fmt, + bprintf_data.bin_args); + bpf_bprintf_cleanup(&bprintf_data); + if (ret < 0) { + scx_error(sch, "(\"%s\", %p, %u) failed to format", fmt, data, data__sz); + return ret; + } + + return ret; +} + +static s32 bstr_format(struct scx_sched *sch, struct scx_bstr_buf *buf, + char *fmt, unsigned long long *data, u32 data__sz) +{ + return __bstr_format(sch, buf->data, buf->line, sizeof(buf->line), + fmt, data, data__sz); +} + +__bpf_kfunc_start_defs(); + +/** + * scx_bpf_exit_bstr - Gracefully exit the BPF scheduler. + * @exit_code: Exit value to pass to user space via struct scx_exit_info. + * @fmt: error message format string + * @data: format string parameters packaged using ___bpf_fill() macro + * @data__sz: @data len, must end in '__sz' for the verifier + * + * Indicate that the BPF scheduler wants to exit gracefully, and initiate ops + * disabling. + */ +__bpf_kfunc void scx_bpf_exit_bstr(s64 exit_code, char *fmt, + unsigned long long *data, u32 data__sz) +{ + struct scx_sched *sch; + unsigned long flags; + + raw_spin_lock_irqsave(&scx_exit_bstr_buf_lock, flags); + sch = rcu_dereference_bh(scx_root); + if (likely(sch) && + bstr_format(sch, &scx_exit_bstr_buf, fmt, data, data__sz) >= 0) + scx_exit(sch, SCX_EXIT_UNREG_BPF, exit_code, "%s", scx_exit_bstr_buf.line); + raw_spin_unlock_irqrestore(&scx_exit_bstr_buf_lock, flags); +} + +/** + * scx_bpf_error_bstr - Indicate fatal error + * @fmt: error message format string + * @data: format string parameters packaged using ___bpf_fill() macro + * @data__sz: @data len, must end in '__sz' for the verifier + * + * Indicate that the BPF scheduler encountered a fatal error and initiate ops + * disabling. + */ +__bpf_kfunc void scx_bpf_error_bstr(char *fmt, unsigned long long *data, + u32 data__sz) +{ + struct scx_sched *sch; + unsigned long flags; + + raw_spin_lock_irqsave(&scx_exit_bstr_buf_lock, flags); + sch = rcu_dereference_bh(scx_root); + if (likely(sch) && + bstr_format(sch, &scx_exit_bstr_buf, fmt, data, data__sz) >= 0) + scx_exit(sch, SCX_EXIT_ERROR_BPF, 0, "%s", scx_exit_bstr_buf.line); + raw_spin_unlock_irqrestore(&scx_exit_bstr_buf_lock, flags); +} + +/** + * scx_bpf_dump_bstr - Generate extra debug dump specific to the BPF scheduler + * @fmt: format string + * @data: format string parameters packaged using ___bpf_fill() macro + * @data__sz: @data len, must end in '__sz' for the verifier + * + * To be called through scx_bpf_dump() helper from ops.dump(), dump_cpu() and + * dump_task() to generate extra debug dump specific to the BPF scheduler. + * + * The extra dump may be multiple lines. A single line may be split over + * multiple calls. The last line is automatically terminated. + */ +__bpf_kfunc void scx_bpf_dump_bstr(char *fmt, unsigned long long *data, + u32 data__sz) +{ + struct scx_sched *sch; + struct scx_dump_data *dd = &scx_dump_data; + struct scx_bstr_buf *buf = &dd->buf; + s32 ret; + + guard(rcu)(); + + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + return; + + if (raw_smp_processor_id() != dd->cpu) { + scx_error(sch, "scx_bpf_dump() must only be called from ops.dump() and friends"); + return; + } + + /* append the formatted string to the line buf */ + ret = __bstr_format(sch, buf->data, buf->line + dd->cursor, + sizeof(buf->line) - dd->cursor, fmt, data, data__sz); + if (ret < 0) { + dump_line(dd->s, "%s[!] (\"%s\", %p, %u) failed to format (%d)", + dd->prefix, fmt, data, data__sz, ret); + return; + } + + dd->cursor += ret; + dd->cursor = min_t(s32, dd->cursor, sizeof(buf->line)); + + if (!dd->cursor) + return; + + /* + * If the line buf overflowed or ends in a newline, flush it into the + * dump. This is to allow the caller to generate a single line over + * multiple calls. As ops_dump_flush() can also handle multiple lines in + * the line buf, the only case which can lead to an unexpected + * truncation is when the caller keeps generating newlines in the middle + * instead of the end consecutively. Don't do that. + */ + if (dd->cursor >= sizeof(buf->line) || buf->line[dd->cursor - 1] == '\n') + ops_dump_flush(); +} + +/** + * scx_bpf_reenqueue_local - Re-enqueue tasks on a local DSQ + * + * Iterate over all of the tasks currently enqueued on the local DSQ of the + * caller's CPU, and re-enqueue them in the BPF scheduler. Can be called from + * anywhere. + */ +__bpf_kfunc void scx_bpf_reenqueue_local___v2(void) +{ + struct rq *rq; + + guard(preempt)(); + + rq = this_rq(); + local_set(&rq->scx.reenq_local_deferred, 1); + schedule_deferred(rq); +} + +/** + * scx_bpf_cpuperf_cap - Query the maximum relative capacity of a CPU + * @cpu: CPU of interest + * + * Return the maximum relative capacity of @cpu in relation to the most + * performant CPU in the system. The return value is in the range [1, + * %SCX_CPUPERF_ONE]. See scx_bpf_cpuperf_cur(). + */ +__bpf_kfunc u32 scx_bpf_cpuperf_cap(s32 cpu) +{ + struct scx_sched *sch; + + guard(rcu)(); + + sch = rcu_dereference(scx_root); + if (likely(sch) && ops_cpu_valid(sch, cpu, NULL)) + return arch_scale_cpu_capacity(cpu); + else + return SCX_CPUPERF_ONE; +} + +/** + * scx_bpf_cpuperf_cur - Query the current relative performance of a CPU + * @cpu: CPU of interest + * + * Return the current relative performance of @cpu in relation to its maximum. + * The return value is in the range [1, %SCX_CPUPERF_ONE]. + * + * The current performance level of a CPU in relation to the maximum performance + * available in the system can be calculated as follows: + * + * scx_bpf_cpuperf_cap() * scx_bpf_cpuperf_cur() / %SCX_CPUPERF_ONE + * + * The result is in the range [1, %SCX_CPUPERF_ONE]. + */ +__bpf_kfunc u32 scx_bpf_cpuperf_cur(s32 cpu) +{ + struct scx_sched *sch; + + guard(rcu)(); + + sch = rcu_dereference(scx_root); + if (likely(sch) && ops_cpu_valid(sch, cpu, NULL)) + return arch_scale_freq_capacity(cpu); + else + return SCX_CPUPERF_ONE; +} + +/** + * scx_bpf_cpuperf_set - Set the relative performance target of a CPU + * @cpu: CPU of interest + * @perf: target performance level [0, %SCX_CPUPERF_ONE] + * + * Set the target performance level of @cpu to @perf. @perf is in linear + * relative scale between 0 and %SCX_CPUPERF_ONE. This determines how the + * schedutil cpufreq governor chooses the target frequency. + * + * The actual performance level chosen, CPU grouping, and the overhead and + * latency of the operations are dependent on the hardware and cpufreq driver in + * use. Consult hardware and cpufreq documentation for more information. The + * current performance level can be monitored using scx_bpf_cpuperf_cur(). + */ +__bpf_kfunc void scx_bpf_cpuperf_set(s32 cpu, u32 perf) +{ + struct scx_sched *sch; + + guard(rcu)(); + + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + return; + + if (unlikely(perf > SCX_CPUPERF_ONE)) { + scx_error(sch, "Invalid cpuperf target %u for CPU %d", perf, cpu); + return; + } + + if (ops_cpu_valid(sch, cpu, NULL)) { + struct rq *rq = cpu_rq(cpu), *locked_rq = scx_locked_rq(); + struct rq_flags rf; + + /* + * When called with an rq lock held, restrict the operation + * to the corresponding CPU to prevent ABBA deadlocks. + */ + if (locked_rq && rq != locked_rq) { + scx_error(sch, "Invalid target CPU %d", cpu); + return; + } + + /* + * If no rq lock is held, allow to operate on any CPU by + * acquiring the corresponding rq lock. + */ + if (!locked_rq) { + rq_lock_irqsave(rq, &rf); + update_rq_clock(rq); + } + + rq->scx.cpuperf_target = perf; + cpufreq_update_util(rq, 0); + + if (!locked_rq) + rq_unlock_irqrestore(rq, &rf); + } +} + +/** + * scx_bpf_nr_node_ids - Return the number of possible node IDs + * + * All valid node IDs in the system are smaller than the returned value. + */ +__bpf_kfunc u32 scx_bpf_nr_node_ids(void) +{ + return nr_node_ids; +} + +/** + * scx_bpf_nr_cpu_ids - Return the number of possible CPU IDs + * + * All valid CPU IDs in the system are smaller than the returned value. + */ +__bpf_kfunc u32 scx_bpf_nr_cpu_ids(void) +{ + return nr_cpu_ids; +} + +/** + * scx_bpf_get_possible_cpumask - Get a referenced kptr to cpu_possible_mask + */ +__bpf_kfunc const struct cpumask *scx_bpf_get_possible_cpumask(void) +{ + return cpu_possible_mask; +} + +/** + * scx_bpf_get_online_cpumask - Get a referenced kptr to cpu_online_mask + */ +__bpf_kfunc const struct cpumask *scx_bpf_get_online_cpumask(void) +{ + return cpu_online_mask; +} + +/** + * scx_bpf_put_cpumask - Release a possible/online cpumask + * @cpumask: cpumask to release + */ +__bpf_kfunc void scx_bpf_put_cpumask(const struct cpumask *cpumask) +{ + /* + * Empty function body because we aren't actually acquiring or releasing + * a reference to a global cpumask, which is read-only in the caller and + * is never released. The acquire / release semantics here are just used + * to make the cpumask is a trusted pointer in the caller. + */ +} + +/** + * scx_bpf_task_running - Is task currently running? + * @p: task of interest + */ +__bpf_kfunc bool scx_bpf_task_running(const struct task_struct *p) +{ + return task_rq(p)->curr == p; +} + +/** + * scx_bpf_task_cpu - CPU a task is currently associated with + * @p: task of interest + */ +__bpf_kfunc s32 scx_bpf_task_cpu(const struct task_struct *p) +{ + return task_cpu(p); +} + +/** + * scx_bpf_cpu_rq - Fetch the rq of a CPU + * @cpu: CPU of the rq + */ +__bpf_kfunc struct rq *scx_bpf_cpu_rq(s32 cpu) +{ + struct scx_sched *sch; + + guard(rcu)(); + + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + return NULL; + + if (!ops_cpu_valid(sch, cpu, NULL)) + return NULL; + + if (!sch->warned_deprecated_rq) { + printk_deferred(KERN_WARNING "sched_ext: %s() is deprecated; " + "use scx_bpf_locked_rq() when holding rq lock " + "or scx_bpf_cpu_curr() to read remote curr safely.\n", __func__); + sch->warned_deprecated_rq = true; + } + + return cpu_rq(cpu); +} + +/** + * scx_bpf_locked_rq - Return the rq currently locked by SCX + * + * Returns the rq if a rq lock is currently held by SCX. + * Otherwise emits an error and returns NULL. + */ +__bpf_kfunc struct rq *scx_bpf_locked_rq(void) +{ + struct scx_sched *sch; + struct rq *rq; + + guard(preempt)(); + + sch = rcu_dereference_sched(scx_root); + if (unlikely(!sch)) + return NULL; + + rq = scx_locked_rq(); + if (!rq) { + scx_error(sch, "accessing rq without holding rq lock"); + return NULL; + } + + return rq; +} + +/** + * scx_bpf_cpu_curr - Return remote CPU's curr task + * @cpu: CPU of interest + * + * Callers must hold RCU read lock (KF_RCU). + */ +__bpf_kfunc struct task_struct *scx_bpf_cpu_curr(s32 cpu) +{ + struct scx_sched *sch; + + guard(rcu)(); + + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + return NULL; + + if (!ops_cpu_valid(sch, cpu, NULL)) + return NULL; + + return rcu_dereference(cpu_rq(cpu)->curr); +} + +/** + * scx_bpf_task_cgroup - Return the sched cgroup of a task + * @p: task of interest + * + * @p->sched_task_group->css.cgroup represents the cgroup @p is associated with + * from the scheduler's POV. SCX operations should use this function to + * determine @p's current cgroup as, unlike following @p->cgroups, + * @p->sched_task_group is protected by @p's rq lock and thus atomic w.r.t. all + * rq-locked operations. Can be called on the parameter tasks of rq-locked + * operations. The restriction guarantees that @p's rq is locked by the caller. + */ +#ifdef CONFIG_CGROUP_SCHED +__bpf_kfunc struct cgroup *scx_bpf_task_cgroup(struct task_struct *p) +{ + struct task_group *tg = p->sched_task_group; + struct cgroup *cgrp = &cgrp_dfl_root.cgrp; + struct scx_sched *sch; + + guard(rcu)(); + + sch = rcu_dereference(scx_root); + if (unlikely(!sch)) + goto out; + + if (!scx_kf_allowed_on_arg_tasks(sch, __SCX_KF_RQ_LOCKED, p)) + goto out; + + cgrp = tg_cgrp(tg); + +out: + cgroup_get(cgrp); + return cgrp; +} +#endif + +/** + * scx_bpf_now - Returns a high-performance monotonically non-decreasing + * clock for the current CPU. The clock returned is in nanoseconds. + * + * It provides the following properties: + * + * 1) High performance: Many BPF schedulers call bpf_ktime_get_ns() frequently + * to account for execution time and track tasks' runtime properties. + * Unfortunately, in some hardware platforms, bpf_ktime_get_ns() -- which + * eventually reads a hardware timestamp counter -- is neither performant nor + * scalable. scx_bpf_now() aims to provide a high-performance clock by + * using the rq clock in the scheduler core whenever possible. + * + * 2) High enough resolution for the BPF scheduler use cases: In most BPF + * scheduler use cases, the required clock resolution is lower than the most + * accurate hardware clock (e.g., rdtsc in x86). scx_bpf_now() basically + * uses the rq clock in the scheduler core whenever it is valid. It considers + * that the rq clock is valid from the time the rq clock is updated + * (update_rq_clock) until the rq is unlocked (rq_unpin_lock). + * + * 3) Monotonically non-decreasing clock for the same CPU: scx_bpf_now() + * guarantees the clock never goes backward when comparing them in the same + * CPU. On the other hand, when comparing clocks in different CPUs, there + * is no such guarantee -- the clock can go backward. It provides a + * monotonically *non-decreasing* clock so that it would provide the same + * clock values in two different scx_bpf_now() calls in the same CPU + * during the same period of when the rq clock is valid. + */ +__bpf_kfunc u64 scx_bpf_now(void) +{ + struct rq *rq; + u64 clock; + + preempt_disable(); + + rq = this_rq(); + if (smp_load_acquire(&rq->scx.flags) & SCX_RQ_CLK_VALID) { + /* + * If the rq clock is valid, use the cached rq clock. + * + * Note that scx_bpf_now() is re-entrant between a process + * context and an interrupt context (e.g., timer interrupt). + * However, we don't need to consider the race between them + * because such race is not observable from a caller. + */ + clock = READ_ONCE(rq->scx.clock); + } else { + /* + * Otherwise, return a fresh rq clock. + * + * The rq clock is updated outside of the rq lock. + * In this case, keep the updated rq clock invalid so the next + * kfunc call outside the rq lock gets a fresh rq clock. + */ + clock = sched_clock_cpu(cpu_of(rq)); + } + + preempt_enable(); + + return clock; +} + +static void scx_read_events(struct scx_sched *sch, struct scx_event_stats *events) +{ + struct scx_event_stats *e_cpu; + int cpu; + + /* Aggregate per-CPU event counters into @events. */ + memset(events, 0, sizeof(*events)); + for_each_possible_cpu(cpu) { + e_cpu = &per_cpu_ptr(sch->pcpu, cpu)->event_stats; + scx_agg_event(events, e_cpu, SCX_EV_SELECT_CPU_FALLBACK); + scx_agg_event(events, e_cpu, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE); + scx_agg_event(events, e_cpu, SCX_EV_DISPATCH_KEEP_LAST); + scx_agg_event(events, e_cpu, SCX_EV_ENQ_SKIP_EXITING); + scx_agg_event(events, e_cpu, SCX_EV_ENQ_SKIP_MIGRATION_DISABLED); + scx_agg_event(events, e_cpu, SCX_EV_REFILL_SLICE_DFL); + scx_agg_event(events, e_cpu, SCX_EV_BYPASS_DURATION); + scx_agg_event(events, e_cpu, SCX_EV_BYPASS_DISPATCH); + scx_agg_event(events, e_cpu, SCX_EV_BYPASS_ACTIVATE); + } +} + +/* + * scx_bpf_events - Get a system-wide event counter to + * @events: output buffer from a BPF program + * @events__sz: @events len, must end in '__sz'' for the verifier + */ +__bpf_kfunc void scx_bpf_events(struct scx_event_stats *events, + size_t events__sz) +{ + struct scx_sched *sch; + struct scx_event_stats e_sys; + + rcu_read_lock(); + sch = rcu_dereference(scx_root); + if (sch) + scx_read_events(sch, &e_sys); + else + memset(&e_sys, 0, sizeof(e_sys)); + rcu_read_unlock(); + + /* + * We cannot entirely trust a BPF-provided size since a BPF program + * might be compiled against a different vmlinux.h, of which + * scx_event_stats would be larger (a newer vmlinux.h) or smaller + * (an older vmlinux.h). Hence, we use the smaller size to avoid + * memory corruption. + */ + events__sz = min(events__sz, sizeof(*events)); + memcpy(events, &e_sys, events__sz); +} + +__bpf_kfunc_end_defs(); + +BTF_KFUNCS_START(scx_kfunc_ids_any) +BTF_ID_FLAGS(func, scx_bpf_task_set_slice, KF_RCU); +BTF_ID_FLAGS(func, scx_bpf_task_set_dsq_vtime, KF_RCU); +BTF_ID_FLAGS(func, scx_bpf_kick_cpu) +BTF_ID_FLAGS(func, scx_bpf_dsq_nr_queued) +BTF_ID_FLAGS(func, scx_bpf_destroy_dsq) +BTF_ID_FLAGS(func, scx_bpf_dsq_peek, KF_RCU_PROTECTED | KF_RET_NULL) +BTF_ID_FLAGS(func, bpf_iter_scx_dsq_new, KF_ITER_NEW | KF_RCU_PROTECTED) +BTF_ID_FLAGS(func, bpf_iter_scx_dsq_next, KF_ITER_NEXT | KF_RET_NULL) +BTF_ID_FLAGS(func, bpf_iter_scx_dsq_destroy, KF_ITER_DESTROY) +BTF_ID_FLAGS(func, scx_bpf_exit_bstr, KF_TRUSTED_ARGS) +BTF_ID_FLAGS(func, scx_bpf_error_bstr, KF_TRUSTED_ARGS) +BTF_ID_FLAGS(func, scx_bpf_dump_bstr, KF_TRUSTED_ARGS) +BTF_ID_FLAGS(func, scx_bpf_reenqueue_local___v2) +BTF_ID_FLAGS(func, scx_bpf_cpuperf_cap) +BTF_ID_FLAGS(func, scx_bpf_cpuperf_cur) +BTF_ID_FLAGS(func, scx_bpf_cpuperf_set) +BTF_ID_FLAGS(func, scx_bpf_nr_node_ids) +BTF_ID_FLAGS(func, scx_bpf_nr_cpu_ids) +BTF_ID_FLAGS(func, scx_bpf_get_possible_cpumask, KF_ACQUIRE) +BTF_ID_FLAGS(func, scx_bpf_get_online_cpumask, KF_ACQUIRE) +BTF_ID_FLAGS(func, scx_bpf_put_cpumask, KF_RELEASE) +BTF_ID_FLAGS(func, scx_bpf_task_running, KF_RCU) +BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU) +BTF_ID_FLAGS(func, scx_bpf_cpu_rq) +BTF_ID_FLAGS(func, scx_bpf_locked_rq, KF_RET_NULL) +BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_RET_NULL | KF_RCU_PROTECTED) +#ifdef CONFIG_CGROUP_SCHED +BTF_ID_FLAGS(func, scx_bpf_task_cgroup, KF_RCU | KF_ACQUIRE) +#endif +BTF_ID_FLAGS(func, scx_bpf_now) +BTF_ID_FLAGS(func, scx_bpf_events, KF_TRUSTED_ARGS) +BTF_KFUNCS_END(scx_kfunc_ids_any) + +static const struct btf_kfunc_id_set scx_kfunc_set_any = { + .owner = THIS_MODULE, + .set = &scx_kfunc_ids_any, +}; + +static int __init scx_init(void) +{ + int ret; + + /* + * kfunc registration can't be done from init_sched_ext_class() as + * register_btf_kfunc_id_set() needs most of the system to be up. + * + * Some kfuncs are context-sensitive and can only be called from + * specific SCX ops. They are grouped into BTF sets accordingly. + * Unfortunately, BPF currently doesn't have a way of enforcing such + * restrictions. Eventually, the verifier should be able to enforce + * them. For now, register them the same and make each kfunc explicitly + * check using scx_kf_allowed(). + */ + if ((ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, + &scx_kfunc_set_enqueue_dispatch)) || + (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, + &scx_kfunc_set_dispatch)) || + (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, + &scx_kfunc_set_cpu_release)) || + (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, + &scx_kfunc_set_unlocked)) || + (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, + &scx_kfunc_set_unlocked)) || + (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, + &scx_kfunc_set_any)) || + (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, + &scx_kfunc_set_any)) || + (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, + &scx_kfunc_set_any))) { + pr_err("sched_ext: Failed to register kfunc sets (%d)\n", ret); + return ret; + } + + ret = scx_idle_init(); + if (ret) { + pr_err("sched_ext: Failed to initialize idle tracking (%d)\n", ret); + return ret; + } + + ret = register_bpf_struct_ops(&bpf_sched_ext_ops, sched_ext_ops); + if (ret) { + pr_err("sched_ext: Failed to register struct_ops (%d)\n", ret); + return ret; + } + + ret = register_pm_notifier(&scx_pm_notifier); + if (ret) { + pr_err("sched_ext: Failed to register PM notifier (%d)\n", ret); + return ret; + } + + scx_kset = kset_create_and_add("sched_ext", &scx_uevent_ops, kernel_kobj); + if (!scx_kset) { + pr_err("sched_ext: Failed to create /sys/kernel/sched_ext\n"); + return -ENOMEM; + } + + ret = sysfs_create_group(&scx_kset->kobj, &scx_global_attr_group); + if (ret < 0) { + pr_err("sched_ext: Failed to add global attributes\n"); + return ret; + } + + if (!alloc_cpumask_var(&scx_bypass_lb_donee_cpumask, GFP_KERNEL) || + !alloc_cpumask_var(&scx_bypass_lb_resched_cpumask, GFP_KERNEL)) { + pr_err("sched_ext: Failed to allocate cpumasks\n"); + return -ENOMEM; + } + + return 0; +} +__initcall(scx_init); |