diff options
Diffstat (limited to 'kernel/rcu/tree_plugin.h')
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 1366 |
1 files changed, 1366 insertions, 0 deletions
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h new file mode 100644 index 000000000000..dbe2d02be824 --- /dev/null +++ b/kernel/rcu/tree_plugin.h @@ -0,0 +1,1366 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * Read-Copy Update mechanism for mutual exclusion (tree-based version) + * Internal non-public definitions that provide either classic + * or preemptible semantics. + * + * Copyright Red Hat, 2009 + * Copyright IBM Corporation, 2009 + * + * Author: Ingo Molnar <mingo@elte.hu> + * Paul E. McKenney <paulmck@linux.ibm.com> + */ + +#include "../locking/rtmutex_common.h" + +static bool rcu_rdp_is_offloaded(struct rcu_data *rdp) +{ + /* + * In order to read the offloaded state of an rdp in a safe + * and stable way and prevent from its value to be changed + * under us, we must either hold the barrier mutex, the cpu + * hotplug lock (read or write) or the nocb lock. Local + * non-preemptible reads are also safe. NOCB kthreads and + * timers have their own means of synchronization against the + * offloaded state updaters. + */ + RCU_NOCB_LOCKDEP_WARN( + !(lockdep_is_held(&rcu_state.barrier_mutex) || + (IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) || + lockdep_is_held(&rdp->nocb_lock) || + lockdep_is_held(&rcu_state.nocb_mutex) || + ((!(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible()) || softirq_count()) && + rdp == this_cpu_ptr(&rcu_data)) || + rcu_current_is_nocb_kthread(rdp)), + "Unsafe read of RCU_NOCB offloaded state" + ); + + return rcu_segcblist_is_offloaded(&rdp->cblist); +} + +/* + * Check the RCU kernel configuration parameters and print informative + * messages about anything out of the ordinary. + */ +static void __init rcu_bootup_announce_oddness(void) +{ + if (IS_ENABLED(CONFIG_RCU_TRACE)) + pr_info("\tRCU event tracing is enabled.\n"); + if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) || + (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32)) + pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d.\n", + RCU_FANOUT); + if (rcu_fanout_exact) + pr_info("\tHierarchical RCU autobalancing is disabled.\n"); + if (IS_ENABLED(CONFIG_PROVE_RCU)) + pr_info("\tRCU lockdep checking is enabled.\n"); + if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) + pr_info("\tRCU strict (and thus non-scalable) grace periods are enabled.\n"); + if (RCU_NUM_LVLS >= 4) + pr_info("\tFour(or more)-level hierarchy is enabled.\n"); + if (RCU_FANOUT_LEAF != 16) + pr_info("\tBuild-time adjustment of leaf fanout to %d.\n", + RCU_FANOUT_LEAF); + if (rcu_fanout_leaf != RCU_FANOUT_LEAF) + pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", + rcu_fanout_leaf); + if (nr_cpu_ids != NR_CPUS) + pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS, nr_cpu_ids); +#ifdef CONFIG_RCU_BOOST + pr_info("\tRCU priority boosting: priority %d delay %d ms.\n", + kthread_prio, CONFIG_RCU_BOOST_DELAY); +#endif + if (blimit != DEFAULT_RCU_BLIMIT) + pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit); + if (qhimark != DEFAULT_RCU_QHIMARK) + pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark); + if (qlowmark != DEFAULT_RCU_QLOMARK) + pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark); + if (qovld != DEFAULT_RCU_QOVLD) + pr_info("\tBoot-time adjustment of callback overload level to %ld.\n", qovld); + if (jiffies_till_first_fqs != ULONG_MAX) + pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs); + if (jiffies_till_next_fqs != ULONG_MAX) + pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs); + if (jiffies_till_sched_qs != ULONG_MAX) + pr_info("\tBoot-time adjustment of scheduler-enlistment delay to %ld jiffies.\n", jiffies_till_sched_qs); + if (rcu_kick_kthreads) + pr_info("\tKick kthreads if too-long grace period.\n"); + if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD)) + pr_info("\tRCU callback double-/use-after-free debug is enabled.\n"); + if (gp_preinit_delay) + pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay); + if (gp_init_delay) + pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay); + if (gp_cleanup_delay) + pr_info("\tRCU debug GP cleanup slowdown %d jiffies.\n", gp_cleanup_delay); + if (nohz_full_patience_delay < 0) { + pr_info("\tRCU NOCB CPU patience negative (%d), resetting to zero.\n", nohz_full_patience_delay); + nohz_full_patience_delay = 0; + } else if (nohz_full_patience_delay > 5 * MSEC_PER_SEC) { + pr_info("\tRCU NOCB CPU patience too large (%d), resetting to %ld.\n", nohz_full_patience_delay, 5 * MSEC_PER_SEC); + nohz_full_patience_delay = 5 * MSEC_PER_SEC; + } else if (nohz_full_patience_delay) { + pr_info("\tRCU NOCB CPU patience set to %d milliseconds.\n", nohz_full_patience_delay); + } + nohz_full_patience_delay_jiffies = msecs_to_jiffies(nohz_full_patience_delay); + if (!use_softirq) + pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n"); + if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG)) + pr_info("\tRCU debug extended QS entry/exit.\n"); + rcupdate_announce_bootup_oddness(); +} + +#ifdef CONFIG_PREEMPT_RCU + +static void rcu_report_exp_rnp(struct rcu_node *rnp, bool wake); +static void rcu_read_unlock_special(struct task_struct *t); + +/* + * Tell them what RCU they are running. + */ +static void __init rcu_bootup_announce(void) +{ + pr_info("Preemptible hierarchical RCU implementation.\n"); + rcu_bootup_announce_oddness(); +} + +/* Flags for rcu_preempt_ctxt_queue() decision table. */ +#define RCU_GP_TASKS 0x8 +#define RCU_EXP_TASKS 0x4 +#define RCU_GP_BLKD 0x2 +#define RCU_EXP_BLKD 0x1 + +/* + * Queues a task preempted within an RCU-preempt read-side critical + * section into the appropriate location within the ->blkd_tasks list, + * depending on the states of any ongoing normal and expedited grace + * periods. The ->gp_tasks pointer indicates which element the normal + * grace period is waiting on (NULL if none), and the ->exp_tasks pointer + * indicates which element the expedited grace period is waiting on (again, + * NULL if none). If a grace period is waiting on a given element in the + * ->blkd_tasks list, it also waits on all subsequent elements. Thus, + * adding a task to the tail of the list blocks any grace period that is + * already waiting on one of the elements. In contrast, adding a task + * to the head of the list won't block any grace period that is already + * waiting on one of the elements. + * + * This queuing is imprecise, and can sometimes make an ongoing grace + * period wait for a task that is not strictly speaking blocking it. + * Given the choice, we needlessly block a normal grace period rather than + * blocking an expedited grace period. + * + * Note that an endless sequence of expedited grace periods still cannot + * indefinitely postpone a normal grace period. Eventually, all of the + * fixed number of preempted tasks blocking the normal grace period that are + * not also blocking the expedited grace period will resume and complete + * their RCU read-side critical sections. At that point, the ->gp_tasks + * pointer will equal the ->exp_tasks pointer, at which point the end of + * the corresponding expedited grace period will also be the end of the + * normal grace period. + */ +static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) + __releases(rnp->lock) /* But leaves rrupts disabled. */ +{ + int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) + + (rnp->exp_tasks ? RCU_EXP_TASKS : 0) + + (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) + + (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0); + struct task_struct *t = current; + + raw_lockdep_assert_held_rcu_node(rnp); + WARN_ON_ONCE(rdp->mynode != rnp); + WARN_ON_ONCE(!rcu_is_leaf_node(rnp)); + /* RCU better not be waiting on newly onlined CPUs! */ + WARN_ON_ONCE(rnp->qsmaskinitnext & ~rnp->qsmaskinit & rnp->qsmask & + rdp->grpmask); + + /* + * Decide where to queue the newly blocked task. In theory, + * this could be an if-statement. In practice, when I tried + * that, it was quite messy. + */ + switch (blkd_state) { + case 0: + case RCU_EXP_TASKS: + case RCU_EXP_TASKS | RCU_GP_BLKD: + case RCU_GP_TASKS: + case RCU_GP_TASKS | RCU_EXP_TASKS: + + /* + * Blocking neither GP, or first task blocking the normal + * GP but not blocking the already-waiting expedited GP. + * Queue at the head of the list to avoid unnecessarily + * blocking the already-waiting GPs. + */ + list_add(&t->rcu_node_entry, &rnp->blkd_tasks); + break; + + case RCU_EXP_BLKD: + case RCU_GP_BLKD: + case RCU_GP_BLKD | RCU_EXP_BLKD: + case RCU_GP_TASKS | RCU_EXP_BLKD: + case RCU_GP_TASKS | RCU_GP_BLKD | RCU_EXP_BLKD: + case RCU_GP_TASKS | RCU_EXP_TASKS | RCU_GP_BLKD | RCU_EXP_BLKD: + + /* + * First task arriving that blocks either GP, or first task + * arriving that blocks the expedited GP (with the normal + * GP already waiting), or a task arriving that blocks + * both GPs with both GPs already waiting. Queue at the + * tail of the list to avoid any GP waiting on any of the + * already queued tasks that are not blocking it. + */ + list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks); + break; + + case RCU_EXP_TASKS | RCU_EXP_BLKD: + case RCU_EXP_TASKS | RCU_GP_BLKD | RCU_EXP_BLKD: + case RCU_GP_TASKS | RCU_EXP_TASKS | RCU_EXP_BLKD: + + /* + * Second or subsequent task blocking the expedited GP. + * The task either does not block the normal GP, or is the + * first task blocking the normal GP. Queue just after + * the first task blocking the expedited GP. + */ + list_add(&t->rcu_node_entry, rnp->exp_tasks); + break; + + case RCU_GP_TASKS | RCU_GP_BLKD: + case RCU_GP_TASKS | RCU_EXP_TASKS | RCU_GP_BLKD: + + /* + * Second or subsequent task blocking the normal GP. + * The task does not block the expedited GP. Queue just + * after the first task blocking the normal GP. + */ + list_add(&t->rcu_node_entry, rnp->gp_tasks); + break; + + default: + + /* Yet another exercise in excessive paranoia. */ + WARN_ON_ONCE(1); + break; + } + + /* + * We have now queued the task. If it was the first one to + * block either grace period, update the ->gp_tasks and/or + * ->exp_tasks pointers, respectively, to reference the newly + * blocked tasks. + */ + if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) { + WRITE_ONCE(rnp->gp_tasks, &t->rcu_node_entry); + WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq); + } + if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD)) + WRITE_ONCE(rnp->exp_tasks, &t->rcu_node_entry); + WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) != + !(rnp->qsmask & rdp->grpmask)); + WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) != + !(rnp->expmask & rdp->grpmask)); + raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */ + + /* + * Report the quiescent state for the expedited GP. This expedited + * GP should not be able to end until we report, so there should be + * no need to check for a subsequent expedited GP. (Though we are + * still in a quiescent state in any case.) + * + * Interrupts are disabled, so ->cpu_no_qs.b.exp cannot change. + */ + if (blkd_state & RCU_EXP_BLKD && rdp->cpu_no_qs.b.exp) + rcu_report_exp_rdp(rdp); + else + WARN_ON_ONCE(rdp->cpu_no_qs.b.exp); + ASSERT_EXCLUSIVE_WRITER_SCOPED(rdp->cpu_no_qs.b.exp); +} + +/* + * Record a preemptible-RCU quiescent state for the specified CPU. + * Note that this does not necessarily mean that the task currently running + * on the CPU is in a quiescent state: Instead, it means that the current + * grace period need not wait on any RCU read-side critical section that + * starts later on this CPU. It also means that if the current task is + * in an RCU read-side critical section, it has already added itself to + * some leaf rcu_node structure's ->blkd_tasks list. In addition to the + * current task, there might be any number of other tasks blocked while + * in an RCU read-side critical section. + * + * Unlike non-preemptible-RCU, quiescent state reports for expedited + * grace periods are handled separately via deferred quiescent states + * and context switch events. + * + * Callers to this function must disable preemption. + */ +static void rcu_qs(void) +{ + RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n"); + if (__this_cpu_read(rcu_data.cpu_no_qs.b.norm)) { + trace_rcu_grace_period(TPS("rcu_preempt"), + __this_cpu_read(rcu_data.gp_seq), + TPS("cpuqs")); + __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false); + barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */ + WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false); + } +} + +/* + * We have entered the scheduler, and the current task might soon be + * context-switched away from. If this task is in an RCU read-side + * critical section, we will no longer be able to rely on the CPU to + * record that fact, so we enqueue the task on the blkd_tasks list. + * The task will dequeue itself when it exits the outermost enclosing + * RCU read-side critical section. Therefore, the current grace period + * cannot be permitted to complete until the blkd_tasks list entries + * predating the current grace period drain, in other words, until + * rnp->gp_tasks becomes NULL. + * + * Caller must disable interrupts. + */ +void rcu_note_context_switch(bool preempt) +{ + struct task_struct *t = current; + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); + struct rcu_node *rnp; + + trace_rcu_utilization(TPS("Start context switch")); + lockdep_assert_irqs_disabled(); + WARN_ONCE(!preempt && rcu_preempt_depth() > 0, "Voluntary context switch within RCU read-side critical section!"); + if (rcu_preempt_depth() > 0 && + !t->rcu_read_unlock_special.b.blocked) { + + /* Possibly blocking in an RCU read-side critical section. */ + rnp = rdp->mynode; + raw_spin_lock_rcu_node(rnp); + t->rcu_read_unlock_special.b.blocked = true; + t->rcu_blocked_node = rnp; + + /* + * Verify the CPU's sanity, trace the preemption, and + * then queue the task as required based on the states + * of any ongoing and expedited grace periods. + */ + WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp)); + WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); + trace_rcu_preempt_task(rcu_state.name, + t->pid, + (rnp->qsmask & rdp->grpmask) + ? rnp->gp_seq + : rcu_seq_snap(&rnp->gp_seq)); + rcu_preempt_ctxt_queue(rnp, rdp); + } else { + rcu_preempt_deferred_qs(t); + } + + /* + * Either we were not in an RCU read-side critical section to + * begin with, or we have now recorded that critical section + * globally. Either way, we can now note a quiescent state + * for this CPU. Again, if we were in an RCU read-side critical + * section, and if that critical section was blocking the current + * grace period, then the fact that the task has been enqueued + * means that we continue to block the current grace period. + */ + rcu_qs(); + if (rdp->cpu_no_qs.b.exp) + rcu_report_exp_rdp(rdp); + rcu_tasks_qs(current, preempt); + trace_rcu_utilization(TPS("End context switch")); +} +EXPORT_SYMBOL_GPL(rcu_note_context_switch); + +/* + * Check for preempted RCU readers blocking the current grace period + * for the specified rcu_node structure. If the caller needs a reliable + * answer, it must hold the rcu_node's ->lock. + */ +static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) +{ + return READ_ONCE(rnp->gp_tasks) != NULL; +} + +/* limit value for ->rcu_read_lock_nesting. */ +#define RCU_NEST_PMAX (INT_MAX / 2) + +static void rcu_preempt_read_enter(void) +{ + WRITE_ONCE(current->rcu_read_lock_nesting, READ_ONCE(current->rcu_read_lock_nesting) + 1); +} + +static int rcu_preempt_read_exit(void) +{ + int ret = READ_ONCE(current->rcu_read_lock_nesting) - 1; + + WRITE_ONCE(current->rcu_read_lock_nesting, ret); + return ret; +} + +static void rcu_preempt_depth_set(int val) +{ + WRITE_ONCE(current->rcu_read_lock_nesting, val); +} + +/* + * Preemptible RCU implementation for rcu_read_lock(). + * Just increment ->rcu_read_lock_nesting, shared state will be updated + * if we block. + */ +void __rcu_read_lock(void) +{ + rcu_preempt_read_enter(); + if (IS_ENABLED(CONFIG_PROVE_LOCKING)) + WARN_ON_ONCE(rcu_preempt_depth() > RCU_NEST_PMAX); + if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && rcu_state.gp_kthread) + WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, true); + barrier(); /* critical section after entry code. */ +} +EXPORT_SYMBOL_GPL(__rcu_read_lock); + +/* + * Preemptible RCU implementation for rcu_read_unlock(). + * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost + * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then + * invoke rcu_read_unlock_special() to clean up after a context switch + * in an RCU read-side critical section and other special cases. + */ +void __rcu_read_unlock(void) +{ + struct task_struct *t = current; + + barrier(); // critical section before exit code. + if (rcu_preempt_read_exit() == 0) { + barrier(); // critical-section exit before .s check. + if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s))) + rcu_read_unlock_special(t); + } + if (IS_ENABLED(CONFIG_PROVE_LOCKING)) { + int rrln = rcu_preempt_depth(); + + WARN_ON_ONCE(rrln < 0 || rrln > RCU_NEST_PMAX); + } +} +EXPORT_SYMBOL_GPL(__rcu_read_unlock); + +/* + * Advance a ->blkd_tasks-list pointer to the next entry, instead + * returning NULL if at the end of the list. + */ +static struct list_head *rcu_next_node_entry(struct task_struct *t, + struct rcu_node *rnp) +{ + struct list_head *np; + + np = t->rcu_node_entry.next; + if (np == &rnp->blkd_tasks) + np = NULL; + return np; +} + +/* + * Return true if the specified rcu_node structure has tasks that were + * preempted within an RCU read-side critical section. + */ +static bool rcu_preempt_has_tasks(struct rcu_node *rnp) +{ + return !list_empty(&rnp->blkd_tasks); +} + +/* + * Report deferred quiescent states. The deferral time can + * be quite short, for example, in the case of the call from + * rcu_read_unlock_special(). + */ +static notrace void +rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) +{ + bool empty_exp; + bool empty_norm; + bool empty_exp_now; + struct list_head *np; + bool drop_boost_mutex = false; + struct rcu_data *rdp; + struct rcu_node *rnp; + union rcu_special special; + + rdp = this_cpu_ptr(&rcu_data); + if (rdp->defer_qs_iw_pending == DEFER_QS_PENDING) + rdp->defer_qs_iw_pending = DEFER_QS_IDLE; + + /* + * If RCU core is waiting for this CPU to exit its critical section, + * report the fact that it has exited. Because irqs are disabled, + * t->rcu_read_unlock_special cannot change. + */ + special = t->rcu_read_unlock_special; + if (!special.s && !rdp->cpu_no_qs.b.exp) { + local_irq_restore(flags); + return; + } + t->rcu_read_unlock_special.s = 0; + if (special.b.need_qs) { + if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) { + rdp->cpu_no_qs.b.norm = false; + rcu_report_qs_rdp(rdp); + udelay(rcu_unlock_delay); + } else { + rcu_qs(); + } + } + + /* + * Respond to a request by an expedited grace period for a + * quiescent state from this CPU. Note that requests from + * tasks are handled when removing the task from the + * blocked-tasks list below. + */ + if (rdp->cpu_no_qs.b.exp) + rcu_report_exp_rdp(rdp); + + /* Clean up if blocked during RCU read-side critical section. */ + if (special.b.blocked) { + + /* + * Remove this task from the list it blocked on. The task + * now remains queued on the rcu_node corresponding to the + * CPU it first blocked on, so there is no longer any need + * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia. + */ + rnp = t->rcu_blocked_node; + raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ + WARN_ON_ONCE(rnp != t->rcu_blocked_node); + WARN_ON_ONCE(!rcu_is_leaf_node(rnp)); + empty_norm = !rcu_preempt_blocked_readers_cgp(rnp); + WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq && + (!empty_norm || rnp->qsmask)); + empty_exp = sync_rcu_exp_done(rnp); + np = rcu_next_node_entry(t, rnp); + list_del_init(&t->rcu_node_entry); + t->rcu_blocked_node = NULL; + trace_rcu_unlock_preempted_task(TPS("rcu_preempt"), + rnp->gp_seq, t->pid); + if (&t->rcu_node_entry == rnp->gp_tasks) + WRITE_ONCE(rnp->gp_tasks, np); + if (&t->rcu_node_entry == rnp->exp_tasks) + WRITE_ONCE(rnp->exp_tasks, np); + if (IS_ENABLED(CONFIG_RCU_BOOST)) { + /* Snapshot ->boost_mtx ownership w/rnp->lock held. */ + drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx.rtmutex) == t; + if (&t->rcu_node_entry == rnp->boost_tasks) + WRITE_ONCE(rnp->boost_tasks, np); + } + + /* + * If this was the last task on the current list, and if + * we aren't waiting on any CPUs, report the quiescent state. + * Note that rcu_report_unblock_qs_rnp() releases rnp->lock, + * so we must take a snapshot of the expedited state. + */ + empty_exp_now = sync_rcu_exp_done(rnp); + if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) { + trace_rcu_quiescent_state_report(TPS("preempt_rcu"), + rnp->gp_seq, + 0, rnp->qsmask, + rnp->level, + rnp->grplo, + rnp->grphi, + !!rnp->gp_tasks); + rcu_report_unblock_qs_rnp(rnp, flags); + } else { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + } + + /* + * If this was the last task on the expedited lists, + * then we need to report up the rcu_node hierarchy. + */ + if (!empty_exp && empty_exp_now) + rcu_report_exp_rnp(rnp, true); + + /* Unboost if we were boosted. */ + if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex) + rt_mutex_futex_unlock(&rnp->boost_mtx.rtmutex); + } else { + local_irq_restore(flags); + } +} + +/* + * Is a deferred quiescent-state pending, and are we also not in + * an RCU read-side critical section? It is the caller's responsibility + * to ensure it is otherwise safe to report any deferred quiescent + * states. The reason for this is that it is safe to report a + * quiescent state during context switch even though preemption + * is disabled. This function cannot be expected to understand these + * nuances, so the caller must handle them. + */ +static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t) +{ + return (__this_cpu_read(rcu_data.cpu_no_qs.b.exp) || + READ_ONCE(t->rcu_read_unlock_special.s)) && + rcu_preempt_depth() == 0; +} + +/* + * Report a deferred quiescent state if needed and safe to do so. + * As with rcu_preempt_need_deferred_qs(), "safe" involves only + * not being in an RCU read-side critical section. The caller must + * evaluate safety in terms of interrupt, softirq, and preemption + * disabling. + */ +notrace void rcu_preempt_deferred_qs(struct task_struct *t) +{ + unsigned long flags; + + if (!rcu_preempt_need_deferred_qs(t)) + return; + local_irq_save(flags); + rcu_preempt_deferred_qs_irqrestore(t, flags); +} + +/* + * Minimal handler to give the scheduler a chance to re-evaluate. + */ +static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp) +{ + struct rcu_data *rdp; + + lockdep_assert_irqs_disabled(); + rdp = container_of(iwp, struct rcu_data, defer_qs_iw); + + /* + * If the IRQ work handler happens to run in the middle of RCU read-side + * critical section, it could be ineffective in getting the scheduler's + * attention to report a deferred quiescent state (the whole point of the + * IRQ work). For this reason, requeue the IRQ work. + * + * Basically, we want to avoid following situation: + * 1. rcu_read_unlock() queues IRQ work (state -> DEFER_QS_PENDING) + * 2. CPU enters new rcu_read_lock() + * 3. IRQ work runs but cannot report QS due to rcu_preempt_depth() > 0 + * 4. rcu_read_unlock() does not re-queue work (state still PENDING) + * 5. Deferred QS reporting does not happen. + */ + if (rcu_preempt_depth() > 0) + WRITE_ONCE(rdp->defer_qs_iw_pending, DEFER_QS_IDLE); +} + +/* + * Check if expedited grace period processing during unlock is needed. + * + * This function determines whether expedited handling is required based on: + * 1. Task blocking an expedited grace period (based on a heuristic, could be + * false-positive, see below.) + * 2. CPU participating in an expedited grace period + * 3. Strict grace period mode requiring expedited handling + * 4. RCU priority deboosting needs when interrupts were disabled + * + * @t: The task being checked + * @rdp: The per-CPU RCU data + * @rnp: The RCU node for this CPU + * @irqs_were_disabled: Whether interrupts were disabled before rcu_read_unlock() + * + * Returns true if expedited processing of the rcu_read_unlock() is needed. + */ +static bool rcu_unlock_needs_exp_handling(struct task_struct *t, + struct rcu_data *rdp, + struct rcu_node *rnp, + bool irqs_were_disabled) +{ + /* + * Check if this task is blocking an expedited grace period. If the + * task was preempted within an RCU read-side critical section and is + * on the expedited grace period blockers list (exp_tasks), we need + * expedited handling to unblock the expedited GP. This is not an exact + * check because 't' might not be on the exp_tasks list at all - its + * just a fast heuristic that can be false-positive sometimes. + */ + if (t->rcu_blocked_node && READ_ONCE(t->rcu_blocked_node->exp_tasks)) + return true; + + /* + * Check if this CPU is participating in an expedited grace period. + * The expmask bitmap tracks which CPUs need to check in for the + * current expedited GP. If our CPU's bit is set, we need expedited + * handling to help complete the expedited GP. + */ + if (rdp->grpmask & READ_ONCE(rnp->expmask)) + return true; + + /* + * In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, all grace periods + * are treated as short for testing purposes even if that means + * disturbing the system more. Check if either: + * - This CPU has not yet reported a quiescent state, or + * - This task was preempted within an RCU critical section + * In either case, require expedited handling for strict GP mode. + */ + if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && + ((rdp->grpmask & READ_ONCE(rnp->qsmask)) || t->rcu_blocked_node)) + return true; + + /* + * RCU priority boosting case: If a task is subject to RCU priority + * boosting and exits an RCU read-side critical section with interrupts + * disabled, we need expedited handling to ensure timely deboosting. + * Without this, a low-priority task could incorrectly run at high + * real-time priority for an extended period degrading real-time + * responsiveness. This applies to all CONFIG_RCU_BOOST=y kernels, + * not just to PREEMPT_RT. + */ + if (IS_ENABLED(CONFIG_RCU_BOOST) && irqs_were_disabled && t->rcu_blocked_node) + return true; + + return false; +} + +/* + * Handle special cases during rcu_read_unlock(), such as needing to + * notify RCU core processing or task having blocked during the RCU + * read-side critical section. + */ +static void rcu_read_unlock_special(struct task_struct *t) +{ + unsigned long flags; + bool irqs_were_disabled; + bool preempt_bh_were_disabled = + !!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)); + + /* NMI handlers cannot block and cannot safely manipulate state. */ + if (in_nmi()) + return; + + local_irq_save(flags); + irqs_were_disabled = irqs_disabled_flags(flags); + if (preempt_bh_were_disabled || irqs_were_disabled) { + bool needs_exp; // Expedited handling needed. + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); + struct rcu_node *rnp = rdp->mynode; + + needs_exp = rcu_unlock_needs_exp_handling(t, rdp, rnp, irqs_were_disabled); + + // Need to defer quiescent state until everything is enabled. + if (use_softirq && (in_hardirq() || (needs_exp && !irqs_were_disabled))) { + // Using softirq, safe to awaken, and either the + // wakeup is free or there is either an expedited + // GP in flight or a potential need to deboost. + raise_softirq_irqoff(RCU_SOFTIRQ); + } else { + // Enabling BH or preempt does reschedule, so... + // Also if no expediting and no possible deboosting, + // slow is OK. Plus nohz_full CPUs eventually get + // tick enabled. + set_need_resched_current(); + if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled && + needs_exp && rdp->defer_qs_iw_pending != DEFER_QS_PENDING && + cpu_online(rdp->cpu)) { + // Get scheduler to re-evaluate and call hooks. + // If !IRQ_WORK, FQS scan will eventually IPI. + rdp->defer_qs_iw_pending = DEFER_QS_PENDING; + irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu); + } + } + local_irq_restore(flags); + return; + } + rcu_preempt_deferred_qs_irqrestore(t, flags); +} + +/* + * Check that the list of blocked tasks for the newly completed grace + * period is in fact empty. It is a serious bug to complete a grace + * period that still has RCU readers blocked! This function must be + * invoked -before- updating this rnp's ->gp_seq. + * + * Also, if there are blocked tasks on the list, they automatically + * block the newly created grace period, so set up ->gp_tasks accordingly. + */ +static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) +{ + struct task_struct *t; + + RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n"); + raw_lockdep_assert_held_rcu_node(rnp); + if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp))) + dump_blkd_tasks(rnp, 10); + if (rcu_preempt_has_tasks(rnp) && + (rnp->qsmaskinit || rnp->wait_blkd_tasks)) { + WRITE_ONCE(rnp->gp_tasks, rnp->blkd_tasks.next); + t = container_of(rnp->gp_tasks, struct task_struct, + rcu_node_entry); + trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"), + rnp->gp_seq, t->pid); + } + WARN_ON_ONCE(rnp->qsmask); +} + +/* + * Check for a quiescent state from the current CPU, including voluntary + * context switches for Tasks RCU. When a task blocks, the task is + * recorded in the corresponding CPU's rcu_node structure, which is checked + * elsewhere, hence this function need only check for quiescent states + * related to the current CPU, not to those related to tasks. + */ +static void rcu_flavor_sched_clock_irq(int user) +{ + struct task_struct *t = current; + + lockdep_assert_irqs_disabled(); + if (rcu_preempt_depth() > 0 || + (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) { + /* No QS, force context switch if deferred. */ + if (rcu_preempt_need_deferred_qs(t)) + set_need_resched_current(); + } else if (rcu_preempt_need_deferred_qs(t)) { + rcu_preempt_deferred_qs(t); /* Report deferred QS. */ + return; + } else if (!WARN_ON_ONCE(rcu_preempt_depth())) { + rcu_qs(); /* Report immediate QS. */ + return; + } + + /* If GP is oldish, ask for help from rcu_read_unlock_special(). */ + if (rcu_preempt_depth() > 0 && + __this_cpu_read(rcu_data.core_needs_qs) && + __this_cpu_read(rcu_data.cpu_no_qs.b.norm) && + !t->rcu_read_unlock_special.b.need_qs && + time_after(jiffies, rcu_state.gp_start + HZ)) + t->rcu_read_unlock_special.b.need_qs = true; +} + +/* + * Check for a task exiting while in a preemptible-RCU read-side + * critical section, clean up if so. No need to issue warnings, as + * debug_check_no_locks_held() already does this if lockdep is enabled. + * Besides, if this function does anything other than just immediately + * return, there was a bug of some sort. Spewing warnings from this + * function is like as not to simply obscure important prior warnings. + */ +void exit_rcu(void) +{ + struct task_struct *t = current; + + if (unlikely(!list_empty(¤t->rcu_node_entry))) { + rcu_preempt_depth_set(1); + barrier(); + WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true); + } else if (unlikely(rcu_preempt_depth())) { + rcu_preempt_depth_set(1); + } else { + return; + } + __rcu_read_unlock(); + rcu_preempt_deferred_qs(current); +} + +/* + * Dump the blocked-tasks state, but limit the list dump to the + * specified number of elements. + */ +static void +dump_blkd_tasks(struct rcu_node *rnp, int ncheck) +{ + int cpu; + int i; + struct list_head *lhp; + struct rcu_data *rdp; + struct rcu_node *rnp1; + + raw_lockdep_assert_held_rcu_node(rnp); + pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n", + __func__, rnp->grplo, rnp->grphi, rnp->level, + (long)READ_ONCE(rnp->gp_seq), (long)rnp->completedqs); + for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent) + pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n", + __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext); + pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n", + __func__, READ_ONCE(rnp->gp_tasks), data_race(rnp->boost_tasks), + READ_ONCE(rnp->exp_tasks)); + pr_info("%s: ->blkd_tasks", __func__); + i = 0; + list_for_each(lhp, &rnp->blkd_tasks) { + pr_cont(" %p", lhp); + if (++i >= ncheck) + break; + } + pr_cont("\n"); + for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) { + rdp = per_cpu_ptr(&rcu_data, cpu); + pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n", + cpu, ".o"[rcu_rdp_cpu_online(rdp)], + (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_state, + (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_state); + } +} + +static void rcu_preempt_deferred_qs_init(struct rcu_data *rdp) +{ + rdp->defer_qs_iw = IRQ_WORK_INIT_HARD(rcu_preempt_deferred_qs_handler); +} +#else /* #ifdef CONFIG_PREEMPT_RCU */ + +/* + * If strict grace periods are enabled, and if the calling + * __rcu_read_unlock() marks the beginning of a quiescent state, immediately + * report that quiescent state and, if requested, spin for a bit. + */ +void rcu_read_unlock_strict(void) +{ + struct rcu_data *rdp; + + if (irqs_disabled() || in_atomic_preempt_off() || !rcu_state.gp_kthread) + return; + + /* + * rcu_report_qs_rdp() can only be invoked with a stable rdp and + * from the local CPU. + * + * The in_atomic_preempt_off() check ensures that we come here holding + * the last preempt_count (which will get dropped once we return to + * __rcu_read_unlock(). + */ + rdp = this_cpu_ptr(&rcu_data); + rdp->cpu_no_qs.b.norm = false; + rcu_report_qs_rdp(rdp); + udelay(rcu_unlock_delay); +} +EXPORT_SYMBOL_GPL(rcu_read_unlock_strict); + +/* + * Tell them what RCU they are running. + */ +static void __init rcu_bootup_announce(void) +{ + pr_info("Hierarchical RCU implementation.\n"); + rcu_bootup_announce_oddness(); +} + +/* + * Note a quiescent state for PREEMPTION=n. Because we do not need to know + * how many quiescent states passed, just if there was at least one since + * the start of the grace period, this just sets a flag. The caller must + * have disabled preemption. + */ +static void rcu_qs(void) +{ + RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!"); + if (!__this_cpu_read(rcu_data.cpu_no_qs.s)) + return; + trace_rcu_grace_period(TPS("rcu_sched"), + __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs")); + __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false); + if (__this_cpu_read(rcu_data.cpu_no_qs.b.exp)) + rcu_report_exp_rdp(this_cpu_ptr(&rcu_data)); +} + +/* + * Register an urgently needed quiescent state. If there is an + * emergency, invoke rcu_momentary_eqs() to do a heavy-weight + * dyntick-idle quiescent state visible to other CPUs, which will in + * some cases serve for expedited as well as normal grace periods. + * Either way, register a lightweight quiescent state. + */ +void rcu_all_qs(void) +{ + unsigned long flags; + + if (!raw_cpu_read(rcu_data.rcu_urgent_qs)) + return; + preempt_disable(); // For CONFIG_PREEMPT_COUNT=y kernels + /* Load rcu_urgent_qs before other flags. */ + if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) { + preempt_enable(); + return; + } + this_cpu_write(rcu_data.rcu_urgent_qs, false); + if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) { + local_irq_save(flags); + rcu_momentary_eqs(); + local_irq_restore(flags); + } + rcu_qs(); + preempt_enable(); +} +EXPORT_SYMBOL_GPL(rcu_all_qs); + +/* + * Note a PREEMPTION=n context switch. The caller must have disabled interrupts. + */ +void rcu_note_context_switch(bool preempt) +{ + trace_rcu_utilization(TPS("Start context switch")); + rcu_qs(); + /* Load rcu_urgent_qs before other flags. */ + if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) + goto out; + this_cpu_write(rcu_data.rcu_urgent_qs, false); + if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) + rcu_momentary_eqs(); +out: + rcu_tasks_qs(current, preempt); + trace_rcu_utilization(TPS("End context switch")); +} +EXPORT_SYMBOL_GPL(rcu_note_context_switch); + +/* + * Because preemptible RCU does not exist, there are never any preempted + * RCU readers. + */ +static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) +{ + return 0; +} + +/* + * Because there is no preemptible RCU, there can be no readers blocked. + */ +static bool rcu_preempt_has_tasks(struct rcu_node *rnp) +{ + return false; +} + +/* + * Because there is no preemptible RCU, there can be no deferred quiescent + * states. + */ +static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t) +{ + return false; +} + +// Except that we do need to respond to a request by an expedited +// grace period for a quiescent state from this CPU. Note that in +// non-preemptible kernels, there can be no context switches within RCU +// read-side critical sections, which in turn means that the leaf rcu_node +// structure's blocked-tasks list is always empty. is therefore no need to +// actually check it. Instead, a quiescent state from this CPU suffices, +// and this function is only called from such a quiescent state. +notrace void rcu_preempt_deferred_qs(struct task_struct *t) +{ + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); + + if (READ_ONCE(rdp->cpu_no_qs.b.exp)) + rcu_report_exp_rdp(rdp); +} + +/* + * Because there is no preemptible RCU, there can be no readers blocked, + * so there is no need to check for blocked tasks. So check only for + * bogus qsmask values. + */ +static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) +{ + WARN_ON_ONCE(rnp->qsmask); +} + +/* + * Check to see if this CPU is in a non-context-switch quiescent state, + * namely user mode and idle loop. + */ +static void rcu_flavor_sched_clock_irq(int user) +{ + if (user || rcu_is_cpu_rrupt_from_idle() || + (IS_ENABLED(CONFIG_PREEMPT_COUNT) && + (preempt_count() == HARDIRQ_OFFSET))) { + + /* + * Get here if this CPU took its interrupt from user + * mode, from the idle loop without this being a nested + * interrupt, or while not holding the task preempt count + * (with PREEMPT_COUNT=y). In this case, the CPU is in a + * quiescent state, so note it. + * + * No memory barrier is required here because rcu_qs() + * references only CPU-local variables that other CPUs + * neither access nor modify, at least not while the + * corresponding CPU is online. + */ + rcu_qs(); + } +} + +/* + * Because preemptible RCU does not exist, tasks cannot possibly exit + * while in preemptible RCU read-side critical sections. + */ +void exit_rcu(void) +{ +} + +/* + * Dump the guaranteed-empty blocked-tasks state. Trust but verify. + */ +static void +dump_blkd_tasks(struct rcu_node *rnp, int ncheck) +{ + WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks)); +} + +static void rcu_preempt_deferred_qs_init(struct rcu_data *rdp) { } + +#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ + +/* + * If boosting, set rcuc kthreads to realtime priority. + */ +static void rcu_cpu_kthread_setup(unsigned int cpu) +{ + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); +#ifdef CONFIG_RCU_BOOST + struct sched_param sp; + + sp.sched_priority = kthread_prio; + sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); +#endif /* #ifdef CONFIG_RCU_BOOST */ + + WRITE_ONCE(rdp->rcuc_activity, jiffies); +} + +static bool rcu_is_callbacks_nocb_kthread(struct rcu_data *rdp) +{ +#ifdef CONFIG_RCU_NOCB_CPU + return rdp->nocb_cb_kthread == current; +#else + return false; +#endif +} + +/* + * Is the current CPU running the RCU-callbacks kthread? + * Caller must have preemption disabled. + */ +static bool rcu_is_callbacks_kthread(struct rcu_data *rdp) +{ + return rdp->rcu_cpu_kthread_task == current || + rcu_is_callbacks_nocb_kthread(rdp); +} + +#ifdef CONFIG_RCU_BOOST + +/* + * Carry out RCU priority boosting on the task indicated by ->exp_tasks + * or ->boost_tasks, advancing the pointer to the next task in the + * ->blkd_tasks list. + * + * Note that irqs must be enabled: boosting the task can block. + * Returns 1 if there are more tasks needing to be boosted. + */ +static int rcu_boost(struct rcu_node *rnp) +{ + unsigned long flags; + struct task_struct *t; + struct list_head *tb; + + if (READ_ONCE(rnp->exp_tasks) == NULL && + READ_ONCE(rnp->boost_tasks) == NULL) + return 0; /* Nothing left to boost. */ + + raw_spin_lock_irqsave_rcu_node(rnp, flags); + + /* + * Recheck under the lock: all tasks in need of boosting + * might exit their RCU read-side critical sections on their own. + */ + if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + return 0; + } + + /* + * Preferentially boost tasks blocking expedited grace periods. + * This cannot starve the normal grace periods because a second + * expedited grace period must boost all blocked tasks, including + * those blocking the pre-existing normal grace period. + */ + if (rnp->exp_tasks != NULL) + tb = rnp->exp_tasks; + else + tb = rnp->boost_tasks; + + /* + * We boost task t by manufacturing an rt_mutex that appears to + * be held by task t. We leave a pointer to that rt_mutex where + * task t can find it, and task t will release the mutex when it + * exits its outermost RCU read-side critical section. Then + * simply acquiring this artificial rt_mutex will boost task + * t's priority. (Thanks to tglx for suggesting this approach!) + * + * Note that task t must acquire rnp->lock to remove itself from + * the ->blkd_tasks list, which it will do from exit() if from + * nowhere else. We therefore are guaranteed that task t will + * stay around at least until we drop rnp->lock. Note that + * rnp->lock also resolves races between our priority boosting + * and task t's exiting its outermost RCU read-side critical + * section. + */ + t = container_of(tb, struct task_struct, rcu_node_entry); + rt_mutex_init_proxy_locked(&rnp->boost_mtx.rtmutex, t); + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + /* Lock only for side effect: boosts task t's priority. */ + rt_mutex_lock(&rnp->boost_mtx); + rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */ + rnp->n_boosts++; + + return READ_ONCE(rnp->exp_tasks) != NULL || + READ_ONCE(rnp->boost_tasks) != NULL; +} + +/* + * Priority-boosting kthread, one per leaf rcu_node. + */ +static int rcu_boost_kthread(void *arg) +{ + struct rcu_node *rnp = (struct rcu_node *)arg; + int spincnt = 0; + int more2boost; + + trace_rcu_utilization(TPS("Start boost kthread@init")); + for (;;) { + WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING); + trace_rcu_utilization(TPS("End boost kthread@rcu_wait")); + rcu_wait(READ_ONCE(rnp->boost_tasks) || + READ_ONCE(rnp->exp_tasks)); + trace_rcu_utilization(TPS("Start boost kthread@rcu_wait")); + WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING); + more2boost = rcu_boost(rnp); + if (more2boost) + spincnt++; + else + spincnt = 0; + if (spincnt > 10) { + WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_YIELDING); + trace_rcu_utilization(TPS("End boost kthread@rcu_yield")); + schedule_timeout_idle(2); + trace_rcu_utilization(TPS("Start boost kthread@rcu_yield")); + spincnt = 0; + } + } + /* NOTREACHED */ + trace_rcu_utilization(TPS("End boost kthread@notreached")); + return 0; +} + +/* + * Check to see if it is time to start boosting RCU readers that are + * blocking the current grace period, and, if so, tell the per-rcu_node + * kthread to start boosting them. If there is an expedited grace + * period in progress, it is always time to boost. + * + * The caller must hold rnp->lock, which this function releases. + * The ->boost_kthread_task is immortal, so we don't need to worry + * about it going away. + */ +static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) + __releases(rnp->lock) +{ + raw_lockdep_assert_held_rcu_node(rnp); + if (!rnp->boost_kthread_task || + (!rcu_preempt_blocked_readers_cgp(rnp) && !rnp->exp_tasks)) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + return; + } + if (rnp->exp_tasks != NULL || + (rnp->gp_tasks != NULL && + rnp->boost_tasks == NULL && + rnp->qsmask == 0 && + (!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld || + IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)))) { + if (rnp->exp_tasks == NULL) + WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks); + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + rcu_wake_cond(rnp->boost_kthread_task, + READ_ONCE(rnp->boost_kthread_status)); + } else { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + } +} + +#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) + +/* + * Do priority-boost accounting for the start of a new grace period. + */ +static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) +{ + rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; +} + +/* + * Create an RCU-boost kthread for the specified node if one does not + * already exist. We only create this kthread for preemptible RCU. + */ +static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp) +{ + unsigned long flags; + int rnp_index = rnp - rcu_get_root(); + struct sched_param sp; + struct task_struct *t; + + if (rnp->boost_kthread_task) + return; + + t = kthread_create(rcu_boost_kthread, (void *)rnp, + "rcub/%d", rnp_index); + if (WARN_ON_ONCE(IS_ERR(t))) + return; + + raw_spin_lock_irqsave_rcu_node(rnp, flags); + rnp->boost_kthread_task = t; + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + + sp.sched_priority = kthread_prio; + sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); + rcu_thread_affine_rnp(t, rnp); + wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ +} + +#else /* #ifdef CONFIG_RCU_BOOST */ + +static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) + __releases(rnp->lock) +{ + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); +} + +static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) +{ +} + +static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp) +{ +} + +#endif /* #else #ifdef CONFIG_RCU_BOOST */ + +/* + * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the + * grace-period kthread will do force_quiescent_state() processing? + * The idea is to avoid waking up RCU core processing on such a + * CPU unless the grace period has extended for too long. + * + * This code relies on the fact that all NO_HZ_FULL CPUs are also + * RCU_NOCB_CPU CPUs. + */ +static bool rcu_nohz_full_cpu(void) +{ +#ifdef CONFIG_NO_HZ_FULL + if (tick_nohz_full_cpu(smp_processor_id()) && + (!rcu_gp_in_progress() || + time_before(jiffies, READ_ONCE(rcu_state.gp_start) + HZ))) + return true; +#endif /* #ifdef CONFIG_NO_HZ_FULL */ + return false; +} + +/* + * Bind the RCU grace-period kthreads to the housekeeping CPU. + */ +static void rcu_bind_gp_kthread(void) +{ + if (!tick_nohz_full_enabled()) + return; + housekeeping_affine(current, HK_TYPE_RCU); +} |