diff options
Diffstat (limited to 'kernel/rcu/tree_plugin.h')
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 2191 |
1 files changed, 410 insertions, 1781 deletions
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 1b3dd2fc0cd6..dbe2d02be824 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1,67 +1,42 @@ +/* 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. * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License as published by - * the Free Software Foundation; either version 2 of the License, or - * (at your option) any later version. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License - * along with this program; if not, you can access it online at - * http://www.gnu.org/licenses/gpl-2.0.html. - * * Copyright Red Hat, 2009 * Copyright IBM Corporation, 2009 * * Author: Ingo Molnar <mingo@elte.hu> - * Paul E. McKenney <paulmck@linux.vnet.ibm.com> + * Paul E. McKenney <paulmck@linux.ibm.com> */ -#include <linux/delay.h> -#include <linux/gfp.h> -#include <linux/oom.h> -#include <linux/sched/debug.h> -#include <linux/smpboot.h> -#include <linux/sched/isolation.h> -#include <uapi/linux/sched/types.h> -#include "../time/tick-internal.h" - -#ifdef CONFIG_RCU_BOOST - #include "../locking/rtmutex_common.h" -/* - * Control variables for per-CPU and per-rcu_node kthreads. - */ -static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task); -DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status); -DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops); -DEFINE_PER_CPU(char, rcu_cpu_has_work); - -#else /* #ifdef CONFIG_RCU_BOOST */ - -/* - * Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST, - * all uses are in dead code. Provide a definition to keep the compiler - * happy, but add WARN_ON_ONCE() to complain if used in the wrong place. - * This probably needs to be excluded from -rt builds. - */ -#define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; }) -#define rt_mutex_futex_unlock(x) WARN_ON_ONCE(1) - -#endif /* #else #ifdef CONFIG_RCU_BOOST */ +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" + ); -#ifdef CONFIG_RCU_NOCB_CPU -static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ -static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ -#endif /* #ifdef CONFIG_RCU_NOCB_CPU */ + return rcu_segcblist_is_offloaded(&rdp->cblist); +} /* * Check the RCU kernel configuration parameters and print informative @@ -77,10 +52,10 @@ static void __init rcu_bootup_announce_oddness(void) RCU_FANOUT); if (rcu_fanout_exact) pr_info("\tHierarchical RCU autobalancing is disabled.\n"); - if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ)) - pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\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) @@ -101,6 +76,8 @@ static void __init rcu_bootup_announce_oddness(void) 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) @@ -110,13 +87,25 @@ static void __init rcu_bootup_announce_oddness(void) 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 enabled.\n"); + 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 init slowdown %d jiffies.\n", 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(); @@ -194,9 +183,9 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) switch (blkd_state) { case 0: case RCU_EXP_TASKS: - case RCU_EXP_TASKS + RCU_GP_BLKD: + case RCU_EXP_TASKS | RCU_GP_BLKD: case RCU_GP_TASKS: - case RCU_GP_TASKS + RCU_EXP_TASKS: + case RCU_GP_TASKS | RCU_EXP_TASKS: /* * Blocking neither GP, or first task blocking the normal @@ -209,10 +198,10 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) 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: + 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 @@ -225,9 +214,9 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) 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: + 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. @@ -238,8 +227,8 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) 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: + 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. @@ -263,11 +252,11 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) * blocked tasks. */ if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) { - rnp->gp_tasks = &t->rcu_node_entry; + 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)) - rnp->exp_tasks = &t->rcu_node_entry; + 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) != @@ -279,11 +268,14 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) * 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->deferred_qs) + if (blkd_state & RCU_EXP_BLKD && rdp->cpu_no_qs.b.exp) rcu_report_exp_rdp(rdp); else - WARN_ON_ONCE(rdp->deferred_qs); + WARN_ON_ONCE(rdp->cpu_no_qs.b.exp); + ASSERT_EXCLUSIVE_WRITER_SCOPED(rdp->cpu_no_qs.b.exp); } /* @@ -297,18 +289,22 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) * 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.s)) { + 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_check_callbacks(). */ - current->rcu_read_unlock_special.b.need_qs = false; + barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */ + WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false); } } @@ -331,11 +327,10 @@ void rcu_note_context_switch(bool preempt) struct rcu_data *rdp = this_cpu_ptr(&rcu_data); struct rcu_node *rnp; - barrier(); /* Avoid RCU read-side critical sections leaking down. */ trace_rcu_utilization(TPS("Start context switch")); lockdep_assert_irqs_disabled(); - WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0); - if (t->rcu_read_lock_nesting > 0 && + 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. */ @@ -349,7 +344,7 @@ void rcu_note_context_switch(bool preempt) * then queue the task as required based on the states * of any ongoing and expedited grace periods. */ - WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0); + 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, @@ -357,15 +352,6 @@ void rcu_note_context_switch(bool preempt) ? rnp->gp_seq : rcu_seq_snap(&rnp->gp_seq)); rcu_preempt_ctxt_queue(rnp, rdp); - } else if (t->rcu_read_lock_nesting < 0 && - t->rcu_read_unlock_special.s) { - - /* - * Complete exit from RCU read-side critical section on - * behalf of preempted instance of __rcu_read_unlock(). - */ - rcu_read_unlock_special(t); - rcu_preempt_deferred_qs(t); } else { rcu_preempt_deferred_qs(t); } @@ -380,10 +366,10 @@ void rcu_note_context_switch(bool preempt) * means that we continue to block the current grace period. */ rcu_qs(); - if (rdp->deferred_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")); - barrier(); /* Avoid RCU read-side critical sections leaking up. */ } EXPORT_SYMBOL_GPL(rcu_note_context_switch); @@ -394,14 +380,30 @@ EXPORT_SYMBOL_GPL(rcu_note_context_switch); */ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) { - return rnp->gp_tasks != NULL; + return READ_ONCE(rnp->gp_tasks) != NULL; } -/* Bias and limit values for ->rcu_read_lock_nesting. */ -#define RCU_NEST_BIAS INT_MAX -#define RCU_NEST_NMAX (-INT_MAX / 2) +/* 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 @@ -409,9 +411,11 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) */ void __rcu_read_lock(void) { - current->rcu_read_lock_nesting++; + rcu_preempt_read_enter(); if (IS_ENABLED(CONFIG_PROVE_LOCKING)) - WARN_ON_ONCE(current->rcu_read_lock_nesting > RCU_NEST_PMAX); + 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); @@ -427,21 +431,16 @@ void __rcu_read_unlock(void) { struct task_struct *t = current; - if (t->rcu_read_lock_nesting != 1) { - --t->rcu_read_lock_nesting; - } else { - barrier(); /* critical section before exit code. */ - t->rcu_read_lock_nesting = -RCU_NEST_BIAS; - barrier(); /* assign before ->rcu_read_unlock_special load */ + 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); - barrier(); /* ->rcu_read_unlock_special load before assign */ - t->rcu_read_lock_nesting = 0; } if (IS_ENABLED(CONFIG_PROVE_LOCKING)) { - int rrln = t->rcu_read_lock_nesting; + int rrln = rcu_preempt_depth(); - WARN_ON_ONCE(rrln < 0 && rrln > RCU_NEST_NMAX); + WARN_ON_ONCE(rrln < 0 || rrln > RCU_NEST_PMAX); } } EXPORT_SYMBOL_GPL(__rcu_read_unlock); @@ -475,7 +474,7 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp) * be quite short, for example, in the case of the call from * rcu_read_unlock_special(). */ -static void +static notrace void rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) { bool empty_exp; @@ -487,23 +486,28 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) 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; - rdp = this_cpu_ptr(&rcu_data); - if (!special.s && !rdp->deferred_qs) { + 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) { - rcu_qs(); - t->rcu_read_unlock_special.b.need_qs = false; - if (!t->rcu_read_unlock_special.s && !rdp->deferred_qs) { - local_irq_restore(flags); - return; + 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(); } } @@ -513,17 +517,11 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) * tasks are handled when removing the task from the * blocked-tasks list below. */ - if (rdp->deferred_qs) { + if (rdp->cpu_no_qs.b.exp) rcu_report_exp_rdp(rdp); - if (!t->rcu_read_unlock_special.s) { - local_irq_restore(flags); - return; - } - } /* Clean up if blocked during RCU read-side critical section. */ if (special.b.blocked) { - t->rcu_read_unlock_special.b.blocked = false; /* * Remove this task from the list it blocked on. The task @@ -538,22 +536,21 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) empty_norm = !rcu_preempt_blocked_readers_cgp(rnp); WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq && (!empty_norm || rnp->qsmask)); - empty_exp = sync_rcu_preempt_exp_done(rnp); - smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ + 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) - rnp->gp_tasks = np; + WRITE_ONCE(rnp->gp_tasks, np); if (&t->rcu_node_entry == rnp->exp_tasks) - rnp->exp_tasks = np; + 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) == t; + drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx.rtmutex) == t; if (&t->rcu_node_entry == rnp->boost_tasks) - rnp->boost_tasks = np; + WRITE_ONCE(rnp->boost_tasks, np); } /* @@ -562,7 +559,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) * 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_preempt_exp_done(rnp); + 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, @@ -576,16 +573,16 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } - /* Unboost if we were boosted. */ - if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex) - rt_mutex_futex_unlock(&rnp->boost_mtx); - /* * 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); } @@ -600,11 +597,11 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) * is disabled. This function cannot be expected to understand these * nuances, so the caller must handle them. */ -static bool rcu_preempt_need_deferred_qs(struct task_struct *t) +static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t) { - return (__this_cpu_read(rcu_data.deferred_qs) || + return (__this_cpu_read(rcu_data.cpu_no_qs.b.exp) || READ_ONCE(t->rcu_read_unlock_special.s)) && - t->rcu_read_lock_nesting <= 0; + rcu_preempt_depth() == 0; } /* @@ -614,19 +611,110 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) * evaluate safety in terms of interrupt, softirq, and preemption * disabling. */ -static void rcu_preempt_deferred_qs(struct task_struct *t) +notrace void rcu_preempt_deferred_qs(struct task_struct *t) { unsigned long flags; - bool couldrecurse = t->rcu_read_lock_nesting >= 0; if (!rcu_preempt_need_deferred_qs(t)) return; - if (couldrecurse) - t->rcu_read_lock_nesting -= RCU_NEST_BIAS; local_irq_save(flags); rcu_preempt_deferred_qs_irqrestore(t, flags); - if (couldrecurse) - t->rcu_read_lock_nesting += RCU_NEST_BIAS; +} + +/* + * 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; } /* @@ -637,9 +725,9 @@ static void rcu_preempt_deferred_qs(struct task_struct *t) 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)); - bool irqs_were_disabled; /* NMI handlers cannot block and cannot safely manipulate state. */ if (in_nmi()) @@ -648,123 +736,44 @@ static void rcu_read_unlock_special(struct task_struct *t) local_irq_save(flags); irqs_were_disabled = irqs_disabled_flags(flags); if (preempt_bh_were_disabled || irqs_were_disabled) { - WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, false); - /* Need to defer quiescent state until everything is enabled. */ - if (irqs_were_disabled) { - /* Enabling irqs does not reschedule, so... */ + 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... */ - set_tsk_need_resched(current); - set_preempt_need_resched(); + // 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; } - WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, false); rcu_preempt_deferred_qs_irqrestore(t, flags); } /* - * Dump detailed information for all tasks blocking the current RCU - * grace period on the specified rcu_node structure. - */ -static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) -{ - unsigned long flags; - struct task_struct *t; - - raw_spin_lock_irqsave_rcu_node(rnp, flags); - if (!rcu_preempt_blocked_readers_cgp(rnp)) { - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - return; - } - t = list_entry(rnp->gp_tasks->prev, - struct task_struct, rcu_node_entry); - list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { - /* - * We could be printing a lot while holding a spinlock. - * Avoid triggering hard lockup. - */ - touch_nmi_watchdog(); - sched_show_task(t); - } - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); -} - -/* - * Dump detailed information for all tasks blocking the current RCU - * grace period. - */ -static void rcu_print_detail_task_stall(void) -{ - struct rcu_node *rnp = rcu_get_root(); - - rcu_print_detail_task_stall_rnp(rnp); - rcu_for_each_leaf_node(rnp) - rcu_print_detail_task_stall_rnp(rnp); -} - -static void rcu_print_task_stall_begin(struct rcu_node *rnp) -{ - pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", - rnp->level, rnp->grplo, rnp->grphi); -} - -static void rcu_print_task_stall_end(void) -{ - pr_cont("\n"); -} - -/* - * Scan the current list of tasks blocked within RCU read-side critical - * sections, printing out the tid of each. - */ -static int rcu_print_task_stall(struct rcu_node *rnp) -{ - struct task_struct *t; - int ndetected = 0; - - if (!rcu_preempt_blocked_readers_cgp(rnp)) - return 0; - rcu_print_task_stall_begin(rnp); - t = list_entry(rnp->gp_tasks->prev, - struct task_struct, rcu_node_entry); - list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { - pr_cont(" P%d", t->pid); - ndetected++; - } - rcu_print_task_stall_end(); - return ndetected; -} - -/* - * Scan the current list of tasks blocked within RCU read-side critical - * sections, printing out the tid of each that is blocking the current - * expedited grace period. - */ -static int rcu_print_task_exp_stall(struct rcu_node *rnp) -{ - struct task_struct *t; - int ndetected = 0; - - if (!rnp->exp_tasks) - return 0; - t = list_entry(rnp->exp_tasks->prev, - struct task_struct, rcu_node_entry); - list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { - pr_cont(" P%d", t->pid); - ndetected++; - } - return ndetected; -} - -/* * 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, and the rnp's ->lock - * must be held by the caller. + * 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. @@ -774,11 +783,12 @@ 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)) { - rnp->gp_tasks = rnp->blkd_tasks.next; + 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"), @@ -788,36 +798,32 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) } /* - * Check for a quiescent state from the current CPU. When a task blocks, - * the task is recorded in the corresponding CPU's rcu_node structure, - * which is checked elsewhere. - * - * Caller must disable hard irqs. + * 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_check_callbacks(int user) +static void rcu_flavor_sched_clock_irq(int user) { struct task_struct *t = current; - if (user || rcu_is_cpu_rrupt_from_idle()) { - rcu_note_voluntary_context_switch(current); - } - if (t->rcu_read_lock_nesting > 0 || + 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_tsk_need_resched(t); - set_preempt_need_resched(); - } + 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 (!t->rcu_read_lock_nesting) { + } 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 (t->rcu_read_lock_nesting > 0 && + 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 && @@ -825,69 +831,27 @@ static void rcu_flavor_check_callbacks(int user) t->rcu_read_unlock_special.b.need_qs = true; } -/** - * synchronize_rcu - wait until a grace period has elapsed. - * - * Control will return to the caller some time after a full grace - * period has elapsed, in other words after all currently executing RCU - * read-side critical sections have completed. Note, however, that - * upon return from synchronize_rcu(), the caller might well be executing - * concurrently with new RCU read-side critical sections that began while - * synchronize_rcu() was waiting. RCU read-side critical sections are - * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. - * In addition, regions of code across which interrupts, preemption, or - * softirqs have been disabled also serve as RCU read-side critical - * sections. This includes hardware interrupt handlers, softirq handlers, - * and NMI handlers. - * - * Note that this guarantee implies further memory-ordering guarantees. - * On systems with more than one CPU, when synchronize_rcu() returns, - * each CPU is guaranteed to have executed a full memory barrier since - * the end of its last RCU read-side critical section whose beginning - * preceded the call to synchronize_rcu(). In addition, each CPU having - * an RCU read-side critical section that extends beyond the return from - * synchronize_rcu() is guaranteed to have executed a full memory barrier - * after the beginning of synchronize_rcu() and before the beginning of - * that RCU read-side critical section. Note that these guarantees include - * CPUs that are offline, idle, or executing in user mode, as well as CPUs - * that are executing in the kernel. - * - * Furthermore, if CPU A invoked synchronize_rcu(), which returned - * to its caller on CPU B, then both CPU A and CPU B are guaranteed - * to have executed a full memory barrier during the execution of - * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but - * again only if the system has more than one CPU). - */ -void synchronize_rcu(void) -{ - RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || - lock_is_held(&rcu_lock_map) || - lock_is_held(&rcu_sched_lock_map), - "Illegal synchronize_rcu() in RCU read-side critical section"); - if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) - return; - if (rcu_gp_is_expedited()) - synchronize_rcu_expedited(); - else - wait_rcu_gp(call_rcu); -} -EXPORT_SYMBOL_GPL(synchronize_rcu); - /* * 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. + * 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 (likely(list_empty(¤t->rcu_node_entry))) + 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; - t->rcu_read_lock_nesting = 1; - barrier(); - t->rcu_read_unlock_special.b.blocked = true; + } __rcu_read_unlock(); rcu_preempt_deferred_qs(current); } @@ -902,40 +866,70 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck) int cpu; int i; struct list_head *lhp; - bool onl; 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)rnp->gp_seq, (long)rnp->completedqs); + (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__, rnp->gp_tasks, rnp->boost_tasks, rnp->exp_tasks); + __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 >= 10) + if (++i >= ncheck) break; } pr_cont("\n"); for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) { rdp = per_cpu_ptr(&rcu_data, cpu); - onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp)); pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n", - cpu, ".o"[onl], - (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags, - (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags); + 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) @@ -945,7 +939,7 @@ static void __init rcu_bootup_announce(void) } /* - * Note a quiescent state for PREEMPT=n. Because we do not need to know + * 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. @@ -958,23 +952,16 @@ static void rcu_qs(void) 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)) - return; - __this_cpu_write(rcu_data.cpu_no_qs.b.exp, false); - rcu_report_exp_rdp(this_cpu_ptr(&rcu_data)); + 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_dyntick_idle() to do a heavy-weight + * 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. - * - * The barrier() calls are redundant in the common case when this is - * called externally, but just in case this is called from within this - * file. - * */ void rcu_all_qs(void) { @@ -982,31 +969,28 @@ void rcu_all_qs(void) if (!raw_cpu_read(rcu_data.rcu_urgent_qs)) return; - preempt_disable(); + 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); - barrier(); /* Avoid RCU read-side critical sections leaking down. */ if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) { local_irq_save(flags); - rcu_momentary_dyntick_idle(); + rcu_momentary_eqs(); local_irq_restore(flags); } rcu_qs(); - barrier(); /* Avoid RCU read-side critical sections leaking up. */ preempt_enable(); } EXPORT_SYMBOL_GPL(rcu_all_qs); /* - * Note a PREEMPT=n context switch. The caller must have disabled interrupts. + * Note a PREEMPTION=n context switch. The caller must have disabled interrupts. */ void rcu_note_context_switch(bool preempt) { - barrier(); /* Avoid RCU read-side critical sections leaking down. */ trace_rcu_utilization(TPS("Start context switch")); rcu_qs(); /* Load rcu_urgent_qs before other flags. */ @@ -1014,12 +998,10 @@ void rcu_note_context_switch(bool preempt) goto out; this_cpu_write(rcu_data.rcu_urgent_qs, false); if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) - rcu_momentary_dyntick_idle(); - if (!preempt) - rcu_tasks_qs(current); + rcu_momentary_eqs(); out: + rcu_tasks_qs(current, preempt); trace_rcu_utilization(TPS("End context switch")); - barrier(); /* Avoid RCU read-side critical sections leaking up. */ } EXPORT_SYMBOL_GPL(rcu_note_context_switch); @@ -1044,37 +1026,24 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp) * Because there is no preemptible RCU, there can be no deferred quiescent * states. */ -static bool rcu_preempt_need_deferred_qs(struct task_struct *t) +static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t) { return false; } -static void rcu_preempt_deferred_qs(struct task_struct *t) { } -/* - * Because preemptible RCU does not exist, we never have to check for - * tasks blocked within RCU read-side critical sections. - */ -static void rcu_print_detail_task_stall(void) +// 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) { -} - -/* - * Because preemptible RCU does not exist, we never have to check for - * tasks blocked within RCU read-side critical sections. - */ -static int rcu_print_task_stall(struct rcu_node *rnp) -{ - return 0; -} + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); -/* - * Because preemptible RCU does not exist, we never have to check for - * tasks blocked within RCU read-side critical sections that are - * blocking the current expedited grace period. - */ -static int rcu_print_task_exp_stall(struct rcu_node *rnp) -{ - return 0; + if (READ_ONCE(rdp->cpu_no_qs.b.exp)) + rcu_report_exp_rdp(rdp); } /* @@ -1088,49 +1057,31 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) } /* - * Check to see if this CPU is in a non-context-switch quiescent state - * (user mode or idle loop for rcu, non-softirq execution for rcu_bh). - * Also schedule RCU core processing. - * - * This function must be called from hardirq context. It is normally - * invoked from the scheduling-clock interrupt. + * Check to see if this CPU is in a non-context-switch quiescent state, + * namely user mode and idle loop. */ -static void rcu_flavor_check_callbacks(int user) +static void rcu_flavor_sched_clock_irq(int user) { - if (user || rcu_is_cpu_rrupt_from_idle()) { + 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 or from the idle loop, and if this is not a - * nested interrupt. In this case, the CPU is in - * a quiescent state, so note it. + * 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(); } } -/* PREEMPT=n implementation of synchronize_rcu(). */ -void synchronize_rcu(void) -{ - RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || - lock_is_held(&rcu_lock_map) || - lock_is_held(&rcu_sched_lock_map), - "Illegal synchronize_rcu() in RCU read-side critical section"); - if (rcu_blocking_is_gp()) - return; - if (rcu_gp_is_expedited()) - synchronize_rcu_expedited(); - else - wait_rcu_gp(call_rcu); -} -EXPORT_SYMBOL_GPL(synchronize_rcu); - /* * Because preemptible RCU does not exist, tasks cannot possibly exit * while in preemptible RCU read-side critical sections. @@ -1148,21 +1099,48 @@ 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 void rcu_wake_cond(struct task_struct *t, int status) +static bool rcu_is_callbacks_nocb_kthread(struct rcu_data *rdp) { - /* - * If the thread is yielding, only wake it when this - * is invoked from idle - */ - if (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) - wake_up_process(t); +#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. @@ -1219,11 +1197,12 @@ static int rcu_boost(struct rcu_node *rnp) * section. */ t = container_of(tb, struct task_struct, rcu_node_entry); - rt_mutex_init_proxy_locked(&rnp->boost_mtx, t); + 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; @@ -1240,20 +1219,21 @@ static int rcu_boost_kthread(void *arg) trace_rcu_utilization(TPS("Start boost kthread@init")); for (;;) { - rnp->boost_kthread_status = RCU_KTHREAD_WAITING; + WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING); trace_rcu_utilization(TPS("End boost kthread@rcu_wait")); - rcu_wait(rnp->boost_tasks || rnp->exp_tasks); + rcu_wait(READ_ONCE(rnp->boost_tasks) || + READ_ONCE(rnp->exp_tasks)); trace_rcu_utilization(TPS("Start boost kthread@rcu_wait")); - rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; + WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING); more2boost = rcu_boost(rnp); if (more2boost) spincnt++; else spincnt = 0; if (spincnt > 10) { - rnp->boost_kthread_status = RCU_KTHREAD_YIELDING; + WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_YIELDING); trace_rcu_utilization(TPS("End boost kthread@rcu_yield")); - schedule_timeout_interruptible(2); + schedule_timeout_idle(2); trace_rcu_utilization(TPS("Start boost kthread@rcu_yield")); spincnt = 0; } @@ -1276,10 +1256,9 @@ static int rcu_boost_kthread(void *arg) static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) __releases(rnp->lock) { - struct task_struct *t; - raw_lockdep_assert_held_rcu_node(rnp); - if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { + if (!rnp->boost_kthread_task || + (!rcu_preempt_blocked_readers_cgp(rnp) && !rnp->exp_tasks)) { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return; } @@ -1287,44 +1266,18 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) (rnp->gp_tasks != NULL && rnp->boost_tasks == NULL && rnp->qsmask == 0 && - ULONG_CMP_GE(jiffies, rnp->boost_time))) { + (!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld || + IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)))) { if (rnp->exp_tasks == NULL) - rnp->boost_tasks = rnp->gp_tasks; + WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - t = rnp->boost_kthread_task; - if (t) - rcu_wake_cond(t, rnp->boost_kthread_status); + rcu_wake_cond(rnp->boost_kthread_task, + READ_ONCE(rnp->boost_kthread_status)); } else { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } } -/* - * Wake up the per-CPU kthread to invoke RCU callbacks. - */ -static void invoke_rcu_callbacks_kthread(void) -{ - unsigned long flags; - - local_irq_save(flags); - __this_cpu_write(rcu_cpu_has_work, 1); - if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && - current != __this_cpu_read(rcu_cpu_kthread_task)) { - rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), - __this_cpu_read(rcu_cpu_kthread_status)); - } - local_irq_restore(flags); -} - -/* - * Is the current CPU running the RCU-callbacks kthread? - * Caller must have preemption disabled. - */ -static bool rcu_is_callbacks_kthread(void) -{ - return __this_cpu_read(rcu_cpu_kthread_task) == current; -} - #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) /* @@ -1338,159 +1291,30 @@ static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) /* * Create an RCU-boost kthread for the specified node if one does not * already exist. We only create this kthread for preemptible RCU. - * Returns zero if all is well, a negated errno otherwise. */ -static int rcu_spawn_one_boost_kthread(struct rcu_node *rnp) +static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp) { - int rnp_index = rnp - rcu_get_root(); unsigned long flags; + int rnp_index = rnp - rcu_get_root(); struct sched_param sp; struct task_struct *t; - if (!IS_ENABLED(CONFIG_PREEMPT_RCU)) - return 0; - - if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0) - return 0; + if (rnp->boost_kthread_task) + return; - rcu_state.boost = 1; - if (rnp->boost_kthread_task != NULL) - return 0; t = kthread_create(rcu_boost_kthread, (void *)rnp, "rcub/%d", rnp_index); - if (IS_ERR(t)) - return PTR_ERR(t); + 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. */ - return 0; -} - -static void rcu_kthread_do_work(void) -{ - rcu_do_batch(this_cpu_ptr(&rcu_data)); -} - -static void rcu_cpu_kthread_setup(unsigned int cpu) -{ - struct sched_param sp; - - sp.sched_priority = kthread_prio; - sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); -} - -static void rcu_cpu_kthread_park(unsigned int cpu) -{ - per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; -} - -static int rcu_cpu_kthread_should_run(unsigned int cpu) -{ - return __this_cpu_read(rcu_cpu_has_work); -} - -/* - * Per-CPU kernel thread that invokes RCU callbacks. This replaces - * the RCU softirq used in configurations of RCU that do not support RCU - * priority boosting. - */ -static void rcu_cpu_kthread(unsigned int cpu) -{ - unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status); - char work, *workp = this_cpu_ptr(&rcu_cpu_has_work); - int spincnt; - - for (spincnt = 0; spincnt < 10; spincnt++) { - trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait")); - local_bh_disable(); - *statusp = RCU_KTHREAD_RUNNING; - this_cpu_inc(rcu_cpu_kthread_loops); - local_irq_disable(); - work = *workp; - *workp = 0; - local_irq_enable(); - if (work) - rcu_kthread_do_work(); - local_bh_enable(); - if (*workp == 0) { - trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); - *statusp = RCU_KTHREAD_WAITING; - return; - } - } - *statusp = RCU_KTHREAD_YIELDING; - trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield")); - schedule_timeout_interruptible(2); - trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); - *statusp = RCU_KTHREAD_WAITING; -} - -/* - * Set the per-rcu_node kthread's affinity to cover all CPUs that are - * served by the rcu_node in question. The CPU hotplug lock is still - * held, so the value of rnp->qsmaskinit will be stable. - * - * We don't include outgoingcpu in the affinity set, use -1 if there is - * no outgoing CPU. If there are no CPUs left in the affinity set, - * this function allows the kthread to execute on any CPU. - */ -static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) -{ - struct task_struct *t = rnp->boost_kthread_task; - unsigned long mask = rcu_rnp_online_cpus(rnp); - cpumask_var_t cm; - int cpu; - - if (!t) - return; - if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) - return; - for_each_leaf_node_possible_cpu(rnp, cpu) - if ((mask & leaf_node_cpu_bit(rnp, cpu)) && - cpu != outgoingcpu) - cpumask_set_cpu(cpu, cm); - if (cpumask_weight(cm) == 0) - cpumask_setall(cm); - set_cpus_allowed_ptr(t, cm); - free_cpumask_var(cm); -} - -static struct smp_hotplug_thread rcu_cpu_thread_spec = { - .store = &rcu_cpu_kthread_task, - .thread_should_run = rcu_cpu_kthread_should_run, - .thread_fn = rcu_cpu_kthread, - .thread_comm = "rcuc/%u", - .setup = rcu_cpu_kthread_setup, - .park = rcu_cpu_kthread_park, -}; - -/* - * Spawn boost kthreads -- called as soon as the scheduler is running. - */ -static void __init rcu_spawn_boost_kthreads(void) -{ - struct rcu_node *rnp; - int cpu; - - for_each_possible_cpu(cpu) - per_cpu(rcu_cpu_has_work, cpu) = 0; - if (WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), "%s: Could not start rcub kthread, OOM is now expected behavior\n", __func__)) - return; - rcu_for_each_leaf_node(rnp) - (void)rcu_spawn_one_boost_kthread(rnp); -} - -static void rcu_prepare_kthreads(int cpu) -{ - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); - struct rcu_node *rnp = rdp->mynode; - - /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ - if (rcu_scheduler_fully_active) - (void)rcu_spawn_one_boost_kthread(rnp); } #else /* #ifdef CONFIG_RCU_BOOST */ @@ -1501,1195 +1325,16 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } -static void invoke_rcu_callbacks_kthread(void) -{ - WARN_ON_ONCE(1); -} - -static bool rcu_is_callbacks_kthread(void) -{ - return false; -} - static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) { } -static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) -{ -} - -static void __init rcu_spawn_boost_kthreads(void) -{ -} - -static void rcu_prepare_kthreads(int cpu) +static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp) { } #endif /* #else #ifdef CONFIG_RCU_BOOST */ -#if !defined(CONFIG_RCU_FAST_NO_HZ) - -/* - * Check to see if any future RCU-related work will need to be done - * by the current CPU, even if none need be done immediately, returning - * 1 if so. This function is part of the RCU implementation; it is -not- - * an exported member of the RCU API. - * - * Because we not have RCU_FAST_NO_HZ, just check whether or not this - * CPU has RCU callbacks queued. - */ -int rcu_needs_cpu(u64 basemono, u64 *nextevt) -{ - *nextevt = KTIME_MAX; - return rcu_cpu_has_callbacks(NULL); -} - -/* - * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up - * after it. - */ -static void rcu_cleanup_after_idle(void) -{ -} - -/* - * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, - * is nothing. - */ -static void rcu_prepare_for_idle(void) -{ -} - -/* - * Don't bother keeping a running count of the number of RCU callbacks - * posted because CONFIG_RCU_FAST_NO_HZ=n. - */ -static void rcu_idle_count_callbacks_posted(void) -{ -} - -#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ - -/* - * This code is invoked when a CPU goes idle, at which point we want - * to have the CPU do everything required for RCU so that it can enter - * the energy-efficient dyntick-idle mode. This is handled by a - * state machine implemented by rcu_prepare_for_idle() below. - * - * The following three proprocessor symbols control this state machine: - * - * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted - * to sleep in dyntick-idle mode with RCU callbacks pending. This - * is sized to be roughly one RCU grace period. Those energy-efficiency - * benchmarkers who might otherwise be tempted to set this to a large - * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your - * system. And if you are -that- concerned about energy efficiency, - * just power the system down and be done with it! - * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is - * permitted to sleep in dyntick-idle mode with only lazy RCU - * callbacks pending. Setting this too high can OOM your system. - * - * The values below work well in practice. If future workloads require - * adjustment, they can be converted into kernel config parameters, though - * making the state machine smarter might be a better option. - */ -#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ -#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ - -static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY; -module_param(rcu_idle_gp_delay, int, 0644); -static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY; -module_param(rcu_idle_lazy_gp_delay, int, 0644); - -/* - * Try to advance callbacks on the current CPU, but only if it has been - * awhile since the last time we did so. Afterwards, if there are any - * callbacks ready for immediate invocation, return true. - */ -static bool __maybe_unused rcu_try_advance_all_cbs(void) -{ - bool cbs_ready = false; - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - struct rcu_node *rnp; - - /* Exit early if we advanced recently. */ - if (jiffies == rdp->last_advance_all) - return false; - rdp->last_advance_all = jiffies; - - rnp = rdp->mynode; - - /* - * Don't bother checking unless a grace period has - * completed since we last checked and there are - * callbacks not yet ready to invoke. - */ - if ((rcu_seq_completed_gp(rdp->gp_seq, - rcu_seq_current(&rnp->gp_seq)) || - unlikely(READ_ONCE(rdp->gpwrap))) && - rcu_segcblist_pend_cbs(&rdp->cblist)) - note_gp_changes(rdp); - - if (rcu_segcblist_ready_cbs(&rdp->cblist)) - cbs_ready = true; - return cbs_ready; -} - -/* - * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready - * to invoke. If the CPU has callbacks, try to advance them. Tell the - * caller to set the timeout based on whether or not there are non-lazy - * callbacks. - * - * The caller must have disabled interrupts. - */ -int rcu_needs_cpu(u64 basemono, u64 *nextevt) -{ - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - unsigned long dj; - - lockdep_assert_irqs_disabled(); - - /* Snapshot to detect later posting of non-lazy callback. */ - rdp->nonlazy_posted_snap = rdp->nonlazy_posted; - - /* If no callbacks, RCU doesn't need the CPU. */ - if (!rcu_cpu_has_callbacks(&rdp->all_lazy)) { - *nextevt = KTIME_MAX; - return 0; - } - - /* Attempt to advance callbacks. */ - if (rcu_try_advance_all_cbs()) { - /* Some ready to invoke, so initiate later invocation. */ - invoke_rcu_core(); - return 1; - } - rdp->last_accelerate = jiffies; - - /* Request timer delay depending on laziness, and round. */ - if (!rdp->all_lazy) { - dj = round_up(rcu_idle_gp_delay + jiffies, - rcu_idle_gp_delay) - jiffies; - } else { - dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; - } - *nextevt = basemono + dj * TICK_NSEC; - return 0; -} - -/* - * Prepare a CPU for idle from an RCU perspective. The first major task - * is to sense whether nohz mode has been enabled or disabled via sysfs. - * The second major task is to check to see if a non-lazy callback has - * arrived at a CPU that previously had only lazy callbacks. The third - * major task is to accelerate (that is, assign grace-period numbers to) - * any recently arrived callbacks. - * - * The caller must have disabled interrupts. - */ -static void rcu_prepare_for_idle(void) -{ - bool needwake; - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - struct rcu_node *rnp; - int tne; - - lockdep_assert_irqs_disabled(); - if (rcu_is_nocb_cpu(smp_processor_id())) - return; - - /* Handle nohz enablement switches conservatively. */ - tne = READ_ONCE(tick_nohz_active); - if (tne != rdp->tick_nohz_enabled_snap) { - if (rcu_cpu_has_callbacks(NULL)) - invoke_rcu_core(); /* force nohz to see update. */ - rdp->tick_nohz_enabled_snap = tne; - return; - } - if (!tne) - return; - - /* - * If a non-lazy callback arrived at a CPU having only lazy - * callbacks, invoke RCU core for the side-effect of recalculating - * idle duration on re-entry to idle. - */ - if (rdp->all_lazy && - rdp->nonlazy_posted != rdp->nonlazy_posted_snap) { - rdp->all_lazy = false; - rdp->nonlazy_posted_snap = rdp->nonlazy_posted; - invoke_rcu_core(); - return; - } - - /* - * If we have not yet accelerated this jiffy, accelerate all - * callbacks on this CPU. - */ - if (rdp->last_accelerate == jiffies) - return; - rdp->last_accelerate = jiffies; - if (rcu_segcblist_pend_cbs(&rdp->cblist)) { - rnp = rdp->mynode; - raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ - needwake = rcu_accelerate_cbs(rnp, rdp); - raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ - if (needwake) - rcu_gp_kthread_wake(); - } -} - -/* - * Clean up for exit from idle. Attempt to advance callbacks based on - * any grace periods that elapsed while the CPU was idle, and if any - * callbacks are now ready to invoke, initiate invocation. - */ -static void rcu_cleanup_after_idle(void) -{ - lockdep_assert_irqs_disabled(); - if (rcu_is_nocb_cpu(smp_processor_id())) - return; - if (rcu_try_advance_all_cbs()) - invoke_rcu_core(); -} - -/* - * Keep a running count of the number of non-lazy callbacks posted - * on this CPU. This running counter (which is never decremented) allows - * rcu_prepare_for_idle() to detect when something out of the idle loop - * posts a callback, even if an equal number of callbacks are invoked. - * Of course, callbacks should only be posted from within a trace event - * designed to be called from idle or from within RCU_NONIDLE(). - */ -static void rcu_idle_count_callbacks_posted(void) -{ - __this_cpu_add(rcu_data.nonlazy_posted, 1); -} - -#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ - -#ifdef CONFIG_RCU_FAST_NO_HZ - -static void print_cpu_stall_fast_no_hz(char *cp, int cpu) -{ - struct rcu_data *rdp = &per_cpu(rcu_data, cpu); - unsigned long nlpd = rdp->nonlazy_posted - rdp->nonlazy_posted_snap; - - sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c", - rdp->last_accelerate & 0xffff, jiffies & 0xffff, - ulong2long(nlpd), - rdp->all_lazy ? 'L' : '.', - rdp->tick_nohz_enabled_snap ? '.' : 'D'); -} - -#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ - -static void print_cpu_stall_fast_no_hz(char *cp, int cpu) -{ - *cp = '\0'; -} - -#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ - -/* Initiate the stall-info list. */ -static void print_cpu_stall_info_begin(void) -{ - pr_cont("\n"); -} - -/* - * Print out diagnostic information for the specified stalled CPU. - * - * If the specified CPU is aware of the current RCU grace period, then - * print the number of scheduling clock interrupts the CPU has taken - * during the time that it has been aware. Otherwise, print the number - * of RCU grace periods that this CPU is ignorant of, for example, "1" - * if the CPU was aware of the previous grace period. - * - * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. - */ -static void print_cpu_stall_info(int cpu) -{ - unsigned long delta; - char fast_no_hz[72]; - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); - char *ticks_title; - unsigned long ticks_value; - - /* - * We could be printing a lot while holding a spinlock. Avoid - * triggering hard lockup. - */ - touch_nmi_watchdog(); - - ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq); - if (ticks_value) { - ticks_title = "GPs behind"; - } else { - ticks_title = "ticks this GP"; - ticks_value = rdp->ticks_this_gp; - } - print_cpu_stall_fast_no_hz(fast_no_hz, cpu); - delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq); - pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n", - cpu, - "O."[!!cpu_online(cpu)], - "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)], - "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)], - !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' : - rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' : - "!."[!delta], - ticks_value, ticks_title, - rcu_dynticks_snap(rdp) & 0xfff, - rdp->dynticks_nesting, rdp->dynticks_nmi_nesting, - rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), - READ_ONCE(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart, - fast_no_hz); -} - -/* Terminate the stall-info list. */ -static void print_cpu_stall_info_end(void) -{ - pr_err("\t"); -} - -/* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */ -static void zero_cpu_stall_ticks(struct rcu_data *rdp) -{ - rdp->ticks_this_gp = 0; - rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id()); - WRITE_ONCE(rdp->last_fqs_resched, jiffies); -} - -#ifdef CONFIG_RCU_NOCB_CPU - -/* - * Offload callback processing from the boot-time-specified set of CPUs - * specified by rcu_nocb_mask. For each CPU in the set, there is a - * kthread created that pulls the callbacks from the corresponding CPU, - * waits for a grace period to elapse, and invokes the callbacks. - * The no-CBs CPUs do a wake_up() on their kthread when they insert - * a callback into any empty list, unless the rcu_nocb_poll boot parameter - * has been specified, in which case each kthread actively polls its - * CPU. (Which isn't so great for energy efficiency, but which does - * reduce RCU's overhead on that CPU.) - * - * This is intended to be used in conjunction with Frederic Weisbecker's - * adaptive-idle work, which would seriously reduce OS jitter on CPUs - * running CPU-bound user-mode computations. - * - * Offloading of callback processing could also in theory be used as - * an energy-efficiency measure because CPUs with no RCU callbacks - * queued are more aggressive about entering dyntick-idle mode. - */ - - -/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */ -static int __init rcu_nocb_setup(char *str) -{ - alloc_bootmem_cpumask_var(&rcu_nocb_mask); - cpulist_parse(str, rcu_nocb_mask); - return 1; -} -__setup("rcu_nocbs=", rcu_nocb_setup); - -static int __init parse_rcu_nocb_poll(char *arg) -{ - rcu_nocb_poll = true; - return 0; -} -early_param("rcu_nocb_poll", parse_rcu_nocb_poll); - -/* - * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended - * grace period. - */ -static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq) -{ - swake_up_all(sq); -} - -static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp) -{ - return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1]; -} - -static void rcu_init_one_nocb(struct rcu_node *rnp) -{ - init_swait_queue_head(&rnp->nocb_gp_wq[0]); - init_swait_queue_head(&rnp->nocb_gp_wq[1]); -} - -/* Is the specified CPU a no-CBs CPU? */ -bool rcu_is_nocb_cpu(int cpu) -{ - if (cpumask_available(rcu_nocb_mask)) - return cpumask_test_cpu(cpu, rcu_nocb_mask); - return false; -} - -/* - * Kick the leader kthread for this NOCB group. Caller holds ->nocb_lock - * and this function releases it. - */ -static void __wake_nocb_leader(struct rcu_data *rdp, bool force, - unsigned long flags) - __releases(rdp->nocb_lock) -{ - struct rcu_data *rdp_leader = rdp->nocb_leader; - - lockdep_assert_held(&rdp->nocb_lock); - if (!READ_ONCE(rdp_leader->nocb_kthread)) { - raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); - return; - } - if (rdp_leader->nocb_leader_sleep || force) { - /* Prior smp_mb__after_atomic() orders against prior enqueue. */ - WRITE_ONCE(rdp_leader->nocb_leader_sleep, false); - del_timer(&rdp->nocb_timer); - raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); - smp_mb(); /* ->nocb_leader_sleep before swake_up_one(). */ - swake_up_one(&rdp_leader->nocb_wq); - } else { - raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); - } -} - -/* - * Kick the leader kthread for this NOCB group, but caller has not - * acquired locks. - */ -static void wake_nocb_leader(struct rcu_data *rdp, bool force) -{ - unsigned long flags; - - raw_spin_lock_irqsave(&rdp->nocb_lock, flags); - __wake_nocb_leader(rdp, force, flags); -} - -/* - * Arrange to wake the leader kthread for this NOCB group at some - * future time when it is safe to do so. - */ -static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype, - const char *reason) -{ - unsigned long flags; - - raw_spin_lock_irqsave(&rdp->nocb_lock, flags); - if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) - mod_timer(&rdp->nocb_timer, jiffies + 1); - WRITE_ONCE(rdp->nocb_defer_wakeup, waketype); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason); - raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); -} - -/* - * Does the specified CPU need an RCU callback for this invocation - * of rcu_barrier()? - */ -static bool rcu_nocb_cpu_needs_barrier(int cpu) -{ - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); - unsigned long ret; -#ifdef CONFIG_PROVE_RCU - struct rcu_head *rhp; -#endif /* #ifdef CONFIG_PROVE_RCU */ - - /* - * Check count of all no-CBs callbacks awaiting invocation. - * There needs to be a barrier before this function is called, - * but associated with a prior determination that no more - * callbacks would be posted. In the worst case, the first - * barrier in rcu_barrier() suffices (but the caller cannot - * necessarily rely on this, not a substitute for the caller - * getting the concurrency design right!). There must also be - * a barrier between the following load an posting of a callback - * (if a callback is in fact needed). This is associated with an - * atomic_inc() in the caller. - */ - ret = rcu_get_n_cbs_nocb_cpu(rdp); - -#ifdef CONFIG_PROVE_RCU - rhp = READ_ONCE(rdp->nocb_head); - if (!rhp) - rhp = READ_ONCE(rdp->nocb_gp_head); - if (!rhp) - rhp = READ_ONCE(rdp->nocb_follower_head); - - /* Having no rcuo kthread but CBs after scheduler starts is bad! */ - if (!READ_ONCE(rdp->nocb_kthread) && rhp && - rcu_scheduler_fully_active) { - /* RCU callback enqueued before CPU first came online??? */ - pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n", - cpu, rhp->func); - WARN_ON_ONCE(1); - } -#endif /* #ifdef CONFIG_PROVE_RCU */ - - return !!ret; -} - -/* - * Enqueue the specified string of rcu_head structures onto the specified - * CPU's no-CBs lists. The CPU is specified by rdp, the head of the - * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy - * counts are supplied by rhcount and rhcount_lazy. - * - * If warranted, also wake up the kthread servicing this CPUs queues. - */ -static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, - struct rcu_head *rhp, - struct rcu_head **rhtp, - int rhcount, int rhcount_lazy, - unsigned long flags) -{ - int len; - struct rcu_head **old_rhpp; - struct task_struct *t; - - /* Enqueue the callback on the nocb list and update counts. */ - atomic_long_add(rhcount, &rdp->nocb_q_count); - /* rcu_barrier() relies on ->nocb_q_count add before xchg. */ - old_rhpp = xchg(&rdp->nocb_tail, rhtp); - WRITE_ONCE(*old_rhpp, rhp); - atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy); - smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */ - - /* If we are not being polled and there is a kthread, awaken it ... */ - t = READ_ONCE(rdp->nocb_kthread); - if (rcu_nocb_poll || !t) { - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("WakeNotPoll")); - return; - } - len = rcu_get_n_cbs_nocb_cpu(rdp); - if (old_rhpp == &rdp->nocb_head) { - if (!irqs_disabled_flags(flags)) { - /* ... if queue was empty ... */ - wake_nocb_leader(rdp, false); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("WakeEmpty")); - } else { - wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE, - TPS("WakeEmptyIsDeferred")); - } - rdp->qlen_last_fqs_check = 0; - } else if (len > rdp->qlen_last_fqs_check + qhimark) { - /* ... or if many callbacks queued. */ - if (!irqs_disabled_flags(flags)) { - wake_nocb_leader(rdp, true); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("WakeOvf")); - } else { - wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE_FORCE, - TPS("WakeOvfIsDeferred")); - } - rdp->qlen_last_fqs_check = LONG_MAX / 2; - } else { - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot")); - } - return; -} - -/* - * This is a helper for __call_rcu(), which invokes this when the normal - * callback queue is inoperable. If this is not a no-CBs CPU, this - * function returns failure back to __call_rcu(), which can complain - * appropriately. - * - * Otherwise, this function queues the callback where the corresponding - * "rcuo" kthread can find it. - */ -static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, - bool lazy, unsigned long flags) -{ - - if (!rcu_is_nocb_cpu(rdp->cpu)) - return false; - __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags); - if (__is_kfree_rcu_offset((unsigned long)rhp->func)) - trace_rcu_kfree_callback(rcu_state.name, rhp, - (unsigned long)rhp->func, - -atomic_long_read(&rdp->nocb_q_count_lazy), - -rcu_get_n_cbs_nocb_cpu(rdp)); - else - trace_rcu_callback(rcu_state.name, rhp, - -atomic_long_read(&rdp->nocb_q_count_lazy), - -rcu_get_n_cbs_nocb_cpu(rdp)); - - /* - * If called from an extended quiescent state with interrupts - * disabled, invoke the RCU core in order to allow the idle-entry - * deferred-wakeup check to function. - */ - if (irqs_disabled_flags(flags) && - !rcu_is_watching() && - cpu_online(smp_processor_id())) - invoke_rcu_core(); - - return true; -} - -/* - * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is - * not a no-CBs CPU. - */ -static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp, - struct rcu_data *rdp, - unsigned long flags) -{ - lockdep_assert_irqs_disabled(); - if (!rcu_is_nocb_cpu(smp_processor_id())) - return false; /* Not NOCBs CPU, caller must migrate CBs. */ - __call_rcu_nocb_enqueue(my_rdp, rcu_segcblist_head(&rdp->cblist), - rcu_segcblist_tail(&rdp->cblist), - rcu_segcblist_n_cbs(&rdp->cblist), - rcu_segcblist_n_lazy_cbs(&rdp->cblist), flags); - rcu_segcblist_init(&rdp->cblist); - rcu_segcblist_disable(&rdp->cblist); - return true; -} - -/* - * If necessary, kick off a new grace period, and either way wait - * for a subsequent grace period to complete. - */ -static void rcu_nocb_wait_gp(struct rcu_data *rdp) -{ - unsigned long c; - bool d; - unsigned long flags; - bool needwake; - struct rcu_node *rnp = rdp->mynode; - - local_irq_save(flags); - c = rcu_seq_snap(&rcu_state.gp_seq); - if (!rdp->gpwrap && ULONG_CMP_GE(rdp->gp_seq_needed, c)) { - local_irq_restore(flags); - } else { - raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ - needwake = rcu_start_this_gp(rnp, rdp, c); - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - if (needwake) - rcu_gp_kthread_wake(); - } - - /* - * Wait for the grace period. Do so interruptibly to avoid messing - * up the load average. - */ - trace_rcu_this_gp(rnp, rdp, c, TPS("StartWait")); - for (;;) { - swait_event_interruptible_exclusive( - rnp->nocb_gp_wq[rcu_seq_ctr(c) & 0x1], - (d = rcu_seq_done(&rnp->gp_seq, c))); - if (likely(d)) - break; - WARN_ON(signal_pending(current)); - trace_rcu_this_gp(rnp, rdp, c, TPS("ResumeWait")); - } - trace_rcu_this_gp(rnp, rdp, c, TPS("EndWait")); - smp_mb(); /* Ensure that CB invocation happens after GP end. */ -} - -/* - * Leaders come here to wait for additional callbacks to show up. - * This function does not return until callbacks appear. - */ -static void nocb_leader_wait(struct rcu_data *my_rdp) -{ - bool firsttime = true; - unsigned long flags; - bool gotcbs; - struct rcu_data *rdp; - struct rcu_head **tail; - -wait_again: - - /* Wait for callbacks to appear. */ - if (!rcu_nocb_poll) { - trace_rcu_nocb_wake(rcu_state.name, my_rdp->cpu, TPS("Sleep")); - swait_event_interruptible_exclusive(my_rdp->nocb_wq, - !READ_ONCE(my_rdp->nocb_leader_sleep)); - raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags); - my_rdp->nocb_leader_sleep = true; - WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT); - del_timer(&my_rdp->nocb_timer); - raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags); - } else if (firsttime) { - firsttime = false; /* Don't drown trace log with "Poll"! */ - trace_rcu_nocb_wake(rcu_state.name, my_rdp->cpu, TPS("Poll")); - } - - /* - * Each pass through the following loop checks a follower for CBs. - * We are our own first follower. Any CBs found are moved to - * nocb_gp_head, where they await a grace period. - */ - gotcbs = false; - smp_mb(); /* wakeup and _sleep before ->nocb_head reads. */ - for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { - rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head); - if (!rdp->nocb_gp_head) - continue; /* No CBs here, try next follower. */ - - /* Move callbacks to wait-for-GP list, which is empty. */ - WRITE_ONCE(rdp->nocb_head, NULL); - rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head); - gotcbs = true; - } - - /* No callbacks? Sleep a bit if polling, and go retry. */ - if (unlikely(!gotcbs)) { - WARN_ON(signal_pending(current)); - if (rcu_nocb_poll) { - schedule_timeout_interruptible(1); - } else { - trace_rcu_nocb_wake(rcu_state.name, my_rdp->cpu, - TPS("WokeEmpty")); - } - goto wait_again; - } - - /* Wait for one grace period. */ - rcu_nocb_wait_gp(my_rdp); - - /* Each pass through the following loop wakes a follower, if needed. */ - for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { - if (!rcu_nocb_poll && - READ_ONCE(rdp->nocb_head) && - READ_ONCE(my_rdp->nocb_leader_sleep)) { - raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags); - my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/ - raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags); - } - if (!rdp->nocb_gp_head) - continue; /* No CBs, so no need to wake follower. */ - - /* Append callbacks to follower's "done" list. */ - raw_spin_lock_irqsave(&rdp->nocb_lock, flags); - tail = rdp->nocb_follower_tail; - rdp->nocb_follower_tail = rdp->nocb_gp_tail; - *tail = rdp->nocb_gp_head; - raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); - if (rdp != my_rdp && tail == &rdp->nocb_follower_head) { - /* List was empty, so wake up the follower. */ - swake_up_one(&rdp->nocb_wq); - } - } - - /* If we (the leader) don't have CBs, go wait some more. */ - if (!my_rdp->nocb_follower_head) - goto wait_again; -} - -/* - * Followers come here to wait for additional callbacks to show up. - * This function does not return until callbacks appear. - */ -static void nocb_follower_wait(struct rcu_data *rdp) -{ - for (;;) { - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FollowerSleep")); - swait_event_interruptible_exclusive(rdp->nocb_wq, - READ_ONCE(rdp->nocb_follower_head)); - if (smp_load_acquire(&rdp->nocb_follower_head)) { - /* ^^^ Ensure CB invocation follows _head test. */ - return; - } - WARN_ON(signal_pending(current)); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty")); - } -} - -/* - * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes - * callbacks queued by the corresponding no-CBs CPU, however, there is - * an optional leader-follower relationship so that the grace-period - * kthreads don't have to do quite so many wakeups. - */ -static int rcu_nocb_kthread(void *arg) -{ - int c, cl; - unsigned long flags; - struct rcu_head *list; - struct rcu_head *next; - struct rcu_head **tail; - struct rcu_data *rdp = arg; - - /* Each pass through this loop invokes one batch of callbacks */ - for (;;) { - /* Wait for callbacks. */ - if (rdp->nocb_leader == rdp) - nocb_leader_wait(rdp); - else - nocb_follower_wait(rdp); - - /* Pull the ready-to-invoke callbacks onto local list. */ - raw_spin_lock_irqsave(&rdp->nocb_lock, flags); - list = rdp->nocb_follower_head; - rdp->nocb_follower_head = NULL; - tail = rdp->nocb_follower_tail; - rdp->nocb_follower_tail = &rdp->nocb_follower_head; - raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); - if (WARN_ON_ONCE(!list)) - continue; - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeNonEmpty")); - - /* Each pass through the following loop invokes a callback. */ - trace_rcu_batch_start(rcu_state.name, - atomic_long_read(&rdp->nocb_q_count_lazy), - rcu_get_n_cbs_nocb_cpu(rdp), -1); - c = cl = 0; - while (list) { - next = list->next; - /* Wait for enqueuing to complete, if needed. */ - while (next == NULL && &list->next != tail) { - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("WaitQueue")); - schedule_timeout_interruptible(1); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("WokeQueue")); - next = list->next; - } - debug_rcu_head_unqueue(list); - local_bh_disable(); - if (__rcu_reclaim(rcu_state.name, list)) - cl++; - c++; - local_bh_enable(); - cond_resched_tasks_rcu_qs(); - list = next; - } - trace_rcu_batch_end(rcu_state.name, c, !!list, 0, 0, 1); - smp_mb__before_atomic(); /* _add after CB invocation. */ - atomic_long_add(-c, &rdp->nocb_q_count); - atomic_long_add(-cl, &rdp->nocb_q_count_lazy); - } - return 0; -} - -/* Is a deferred wakeup of rcu_nocb_kthread() required? */ -static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) -{ - return READ_ONCE(rdp->nocb_defer_wakeup); -} - -/* Do a deferred wakeup of rcu_nocb_kthread(). */ -static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp) -{ - unsigned long flags; - int ndw; - - raw_spin_lock_irqsave(&rdp->nocb_lock, flags); - if (!rcu_nocb_need_deferred_wakeup(rdp)) { - raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); - return; - } - ndw = READ_ONCE(rdp->nocb_defer_wakeup); - WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT); - __wake_nocb_leader(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DeferredWake")); -} - -/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */ -static void do_nocb_deferred_wakeup_timer(struct timer_list *t) -{ - struct rcu_data *rdp = from_timer(rdp, t, nocb_timer); - - do_nocb_deferred_wakeup_common(rdp); -} - -/* - * Do a deferred wakeup of rcu_nocb_kthread() from fastpath. - * This means we do an inexact common-case check. Note that if - * we miss, ->nocb_timer will eventually clean things up. - */ -static void do_nocb_deferred_wakeup(struct rcu_data *rdp) -{ - if (rcu_nocb_need_deferred_wakeup(rdp)) - do_nocb_deferred_wakeup_common(rdp); -} - -void __init rcu_init_nohz(void) -{ - int cpu; - bool need_rcu_nocb_mask = false; - -#if defined(CONFIG_NO_HZ_FULL) - if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask)) - need_rcu_nocb_mask = true; -#endif /* #if defined(CONFIG_NO_HZ_FULL) */ - - if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) { - if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) { - pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n"); - return; - } - } - if (!cpumask_available(rcu_nocb_mask)) - return; - -#if defined(CONFIG_NO_HZ_FULL) - if (tick_nohz_full_running) - cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask); -#endif /* #if defined(CONFIG_NO_HZ_FULL) */ - - if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { - pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n"); - cpumask_and(rcu_nocb_mask, cpu_possible_mask, - rcu_nocb_mask); - } - if (cpumask_empty(rcu_nocb_mask)) - pr_info("\tOffload RCU callbacks from CPUs: (none).\n"); - else - pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n", - cpumask_pr_args(rcu_nocb_mask)); - if (rcu_nocb_poll) - pr_info("\tPoll for callbacks from no-CBs CPUs.\n"); - - for_each_cpu(cpu, rcu_nocb_mask) - init_nocb_callback_list(per_cpu_ptr(&rcu_data, cpu)); - rcu_organize_nocb_kthreads(); -} - -/* Initialize per-rcu_data variables for no-CBs CPUs. */ -static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) -{ - rdp->nocb_tail = &rdp->nocb_head; - init_swait_queue_head(&rdp->nocb_wq); - rdp->nocb_follower_tail = &rdp->nocb_follower_head; - raw_spin_lock_init(&rdp->nocb_lock); - timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0); -} - -/* - * If the specified CPU is a no-CBs CPU that does not already have its - * rcuo kthread, spawn it. If the CPUs are brought online out of order, - * this can require re-organizing the leader-follower relationships. - */ -static void rcu_spawn_one_nocb_kthread(int cpu) -{ - struct rcu_data *rdp; - struct rcu_data *rdp_last; - struct rcu_data *rdp_old_leader; - struct rcu_data *rdp_spawn = per_cpu_ptr(&rcu_data, cpu); - struct task_struct *t; - - /* - * If this isn't a no-CBs CPU or if it already has an rcuo kthread, - * then nothing to do. - */ - if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread) - return; - - /* If we didn't spawn the leader first, reorganize! */ - rdp_old_leader = rdp_spawn->nocb_leader; - if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) { - rdp_last = NULL; - rdp = rdp_old_leader; - do { - rdp->nocb_leader = rdp_spawn; - if (rdp_last && rdp != rdp_spawn) - rdp_last->nocb_next_follower = rdp; - if (rdp == rdp_spawn) { - rdp = rdp->nocb_next_follower; - } else { - rdp_last = rdp; - rdp = rdp->nocb_next_follower; - rdp_last->nocb_next_follower = NULL; - } - } while (rdp); - rdp_spawn->nocb_next_follower = rdp_old_leader; - } - - /* Spawn the kthread for this CPU. */ - t = kthread_run(rcu_nocb_kthread, rdp_spawn, - "rcuo%c/%d", rcu_state.abbr, cpu); - if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo kthread, OOM is now expected behavior\n", __func__)) - return; - WRITE_ONCE(rdp_spawn->nocb_kthread, t); -} - -/* - * If the specified CPU is a no-CBs CPU that does not already have its - * rcuo kthreads, spawn them. - */ -static void rcu_spawn_all_nocb_kthreads(int cpu) -{ - if (rcu_scheduler_fully_active) - rcu_spawn_one_nocb_kthread(cpu); -} - -/* - * Once the scheduler is running, spawn rcuo kthreads for all online - * no-CBs CPUs. This assumes that the early_initcall()s happen before - * non-boot CPUs come online -- if this changes, we will need to add - * some mutual exclusion. - */ -static void __init rcu_spawn_nocb_kthreads(void) -{ - int cpu; - - for_each_online_cpu(cpu) - rcu_spawn_all_nocb_kthreads(cpu); -} - -/* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */ -static int rcu_nocb_leader_stride = -1; -module_param(rcu_nocb_leader_stride, int, 0444); - -/* - * Initialize leader-follower relationships for all no-CBs CPU. - */ -static void __init rcu_organize_nocb_kthreads(void) -{ - int cpu; - int ls = rcu_nocb_leader_stride; - int nl = 0; /* Next leader. */ - struct rcu_data *rdp; - struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */ - struct rcu_data *rdp_prev = NULL; - - if (!cpumask_available(rcu_nocb_mask)) - return; - if (ls == -1) { - ls = int_sqrt(nr_cpu_ids); - rcu_nocb_leader_stride = ls; - } - - /* - * Each pass through this loop sets up one rcu_data structure. - * Should the corresponding CPU come online in the future, then - * we will spawn the needed set of rcu_nocb_kthread() kthreads. - */ - for_each_cpu(cpu, rcu_nocb_mask) { - rdp = per_cpu_ptr(&rcu_data, cpu); - if (rdp->cpu >= nl) { - /* New leader, set up for followers & next leader. */ - nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls; - rdp->nocb_leader = rdp; - rdp_leader = rdp; - } else { - /* Another follower, link to previous leader. */ - rdp->nocb_leader = rdp_leader; - rdp_prev->nocb_next_follower = rdp; - } - rdp_prev = rdp; - } -} - -/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */ -static bool init_nocb_callback_list(struct rcu_data *rdp) -{ - if (!rcu_is_nocb_cpu(rdp->cpu)) - return false; - - /* If there are early-boot callbacks, move them to nocb lists. */ - if (!rcu_segcblist_empty(&rdp->cblist)) { - rdp->nocb_head = rcu_segcblist_head(&rdp->cblist); - rdp->nocb_tail = rcu_segcblist_tail(&rdp->cblist); - atomic_long_set(&rdp->nocb_q_count, - rcu_segcblist_n_cbs(&rdp->cblist)); - atomic_long_set(&rdp->nocb_q_count_lazy, - rcu_segcblist_n_lazy_cbs(&rdp->cblist)); - rcu_segcblist_init(&rdp->cblist); - } - rcu_segcblist_disable(&rdp->cblist); - return true; -} - -/* - * Bind the current task to the offloaded CPUs. If there are no offloaded - * CPUs, leave the task unbound. Splat if the bind attempt fails. - */ -void rcu_bind_current_to_nocb(void) -{ - if (cpumask_available(rcu_nocb_mask) && cpumask_weight(rcu_nocb_mask)) - WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask)); -} -EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb); - -/* - * Return the number of RCU callbacks still queued from the specified - * CPU, which must be a nocbs CPU. - */ -static unsigned long rcu_get_n_cbs_nocb_cpu(struct rcu_data *rdp) -{ - return atomic_long_read(&rdp->nocb_q_count); -} - -#else /* #ifdef CONFIG_RCU_NOCB_CPU */ - -static bool rcu_nocb_cpu_needs_barrier(int cpu) -{ - WARN_ON_ONCE(1); /* Should be dead code. */ - return false; -} - -static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq) -{ -} - -static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp) -{ - return NULL; -} - -static void rcu_init_one_nocb(struct rcu_node *rnp) -{ -} - -static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, - bool lazy, unsigned long flags) -{ - return false; -} - -static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp, - struct rcu_data *rdp, - unsigned long flags) -{ - return false; -} - -static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) -{ -} - -static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) -{ - return false; -} - -static void do_nocb_deferred_wakeup(struct rcu_data *rdp) -{ -} - -static void rcu_spawn_all_nocb_kthreads(int cpu) -{ -} - -static void __init rcu_spawn_nocb_kthreads(void) -{ -} - -static bool init_nocb_callback_list(struct rcu_data *rdp) -{ - return false; -} - -static unsigned long rcu_get_n_cbs_nocb_cpu(struct rcu_data *rdp) -{ - return 0; -} - -#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ - /* * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the * grace-period kthread will do force_quiescent_state() processing? @@ -2697,14 +1342,14 @@ static unsigned long rcu_get_n_cbs_nocb_cpu(struct rcu_data *rdp) * CPU unless the grace period has extended for too long. * * This code relies on the fact that all NO_HZ_FULL CPUs are also - * CONFIG_RCU_NOCB_CPU CPUs. + * 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() || - ULONG_CMP_LT(jiffies, READ_ONCE(rcu_state.gp_start) + HZ))) + time_before(jiffies, READ_ONCE(rcu_state.gp_start) + HZ))) return true; #endif /* #ifdef CONFIG_NO_HZ_FULL */ return false; @@ -2717,21 +1362,5 @@ static void rcu_bind_gp_kthread(void) { if (!tick_nohz_full_enabled()) return; - housekeeping_affine(current, HK_FLAG_RCU); -} - -/* Record the current task on dyntick-idle entry. */ -static void rcu_dynticks_task_enter(void) -{ -#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) - WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id()); -#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ -} - -/* Record no current task on dyntick-idle exit. */ -static void rcu_dynticks_task_exit(void) -{ -#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) - WRITE_ONCE(current->rcu_tasks_idle_cpu, -1); -#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ + housekeeping_affine(current, HK_TYPE_RCU); } |