| Author | Tokens | Token Proportion | Commits | Commit Proportion |
|---|---|---|---|---|
| Paul E. McKenney | 8914 | 94.68% | 246 | 80.92% |
| Thomas Gleixner | 120 | 1.27% | 4 | 1.32% |
| Steven Rostedt | 51 | 0.54% | 1 | 0.33% |
| Pranith Kumar | 43 | 0.46% | 11 | 3.62% |
| Daniel Wagner | 40 | 0.42% | 1 | 0.33% |
| Paul Gortmaker | 39 | 0.41% | 3 | 0.99% |
| Lai Jiangshan | 28 | 0.30% | 1 | 0.33% |
| Kees Cook | 21 | 0.22% | 1 | 0.33% |
| Rakib Mullick | 16 | 0.17% | 1 | 0.33% |
| Peter Zijlstra | 16 | 0.17% | 4 | 1.32% |
| Boqun Feng | 15 | 0.16% | 2 | 0.66% |
| Tejun Heo | 13 | 0.14% | 2 | 0.66% |
| Frédéric Weisbecker | 13 | 0.14% | 4 | 1.32% |
| Mark Rutland | 12 | 0.13% | 1 | 0.33% |
| Carsten Emde | 7 | 0.07% | 1 | 0.33% |
| Clark Williams | 7 | 0.07% | 1 | 0.33% |
| Shaohua Li | 7 | 0.07% | 1 | 0.33% |
| Sebastian Andrzej Siewior | 7 | 0.07% | 1 | 0.33% |
| Christoph Lameter | 6 | 0.06% | 1 | 0.33% |
| Ingo Molnar | 6 | 0.06% | 2 | 0.66% |
| Byungchul Park | 6 | 0.06% | 2 | 0.66% |
| Mike Galbraith | 6 | 0.06% | 1 | 0.33% |
| Patrick Daly | 4 | 0.04% | 1 | 0.33% |
| Alexander Gordeev | 4 | 0.04% | 1 | 0.33% |
| Joe Perches | 3 | 0.03% | 2 | 0.66% |
| Ding Tianhong | 2 | 0.02% | 1 | 0.33% |
| Antti P. Miettinen | 2 | 0.02% | 1 | 0.33% |
| Matthew Wilcox | 2 | 0.02% | 1 | 0.33% |
| Nicholas Mc Guire | 1 | 0.01% | 1 | 0.33% |
| Paul Bolle | 1 | 0.01% | 1 | 0.33% |
| Linus Torvalds | 1 | 0.01% | 1 | 0.33% |
| Liu Ping Fan | 1 | 0.01% | 1 | 0.33% |
| Alexey Dobriyan | 1 | 0.01% | 1 | 0.33% |
| Total | 9415 | 304 |
/* * 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> */ #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 */ #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 */ /* * 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_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 (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 (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 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); 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)) { 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; 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.) */ if (blkd_state & RCU_EXP_BLKD && rdp->deferred_qs) rcu_report_exp_rdp(rdp); else WARN_ON_ONCE(rdp->deferred_qs); } /* * 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. * * 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)) { 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; } } /* * 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; 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 && !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((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0); 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 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); } /* * 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->deferred_qs) rcu_report_exp_rdp(rdp); trace_rcu_utilization(TPS("End context switch")); barrier(); /* Avoid RCU read-side critical sections leaking up. */ } 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 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) #define RCU_NEST_PMAX (INT_MAX / 2) /* * 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) { current->rcu_read_lock_nesting++; if (IS_ENABLED(CONFIG_PROVE_LOCKING)) WARN_ON_ONCE(current->rcu_read_lock_nesting > RCU_NEST_PMAX); 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; 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 */ 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; WARN_ON_ONCE(rrln < 0 && rrln > RCU_NEST_NMAX); } } 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 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; /* * 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) { local_irq_restore(flags); return; } 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; } } /* * 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->deferred_qs) { 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 * 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_preempt_exp_done(rnp); smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ 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; if (&t->rcu_node_entry == rnp->exp_tasks) 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; if (&t->rcu_node_entry == rnp->boost_tasks) 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_preempt_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); } /* 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); } 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 bool rcu_preempt_need_deferred_qs(struct task_struct *t) { return (__this_cpu_read(rcu_data.deferred_qs) || READ_ONCE(t->rcu_read_unlock_special.s)) && t->rcu_read_lock_nesting <= 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. */ static 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; } /* * 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 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()) return; 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... */ raise_softirq_irqoff(RCU_SOFTIRQ); } else { /* Enabling BH or preempt does reschedule, so... */ set_tsk_need_resched(current); set_preempt_need_resched(); } 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. * * 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"); 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; 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. 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. */ static void rcu_flavor_check_callbacks(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 || (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(); } } else if (rcu_preempt_need_deferred_qs(t)) { rcu_preempt_deferred_qs(t); /* Report deferred QS. */ return; } else if (!t->rcu_read_lock_nesting) { 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 && __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; } /** * 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. */ void exit_rcu(void) { struct task_struct *t = current; if (likely(list_empty(¤t->rcu_node_entry))) return; t->rcu_read_lock_nesting = 1; barrier(); t->rcu_read_unlock_special.b.blocked = true; __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; 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); 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); pr_info("%s: ->blkd_tasks", __func__); i = 0; list_for_each(lhp, &rnp->blkd_tasks) { pr_cont(" %p", lhp); if (++i >= 10) 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); } } #else /* #ifdef CONFIG_PREEMPT_RCU */ /* * 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 PREEMPT=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)) return; __this_cpu_write(rcu_data.cpu_no_qs.b.exp, false); 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 * 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) { unsigned long flags; if (!raw_cpu_read(rcu_data.rcu_urgent_qs)) return; preempt_disable(); /* 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(); 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. */ 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. */ 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_dyntick_idle(); if (!preempt) rcu_tasks_qs(current); out: trace_rcu_utilization(TPS("End context switch")); barrier(); /* Avoid RCU read-side critical sections leaking up. */ } 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 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) { } /* * 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; } /* * 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; } /* * 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 * (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. */ static void rcu_flavor_check_callbacks(int user) { if (user || rcu_is_cpu_rrupt_from_idle()) { /* * 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. * * 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. */ 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)); } #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ #ifdef CONFIG_RCU_BOOST static void rcu_wake_cond(struct task_struct *t, int status) { /* * 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); } /* * 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, 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. */ 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 (;;) { rnp->boost_kthread_status = RCU_KTHREAD_WAITING; trace_rcu_utilization(TPS("End boost kthread@rcu_wait")); rcu_wait(rnp->boost_tasks || rnp->exp_tasks); trace_rcu_utilization(TPS("Start boost kthread@rcu_wait")); 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; trace_rcu_utilization(TPS("End boost kthread@rcu_yield")); schedule_timeout_interruptible(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) { struct task_struct *t; raw_lockdep_assert_held_rcu_node(rnp); if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { 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 && ULONG_CMP_GE(jiffies, rnp->boost_time))) { if (rnp->exp_tasks == NULL) 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); } 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) /* * 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. * Returns zero if all is well, a negated errno otherwise. */ static int rcu_spawn_one_boost_kthread(struct rcu_node *rnp) { int rnp_index = rnp - rcu_get_root(); unsigned long flags; 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; 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); 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); 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 */ 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 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) { } #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? * 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 * CONFIG_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))) 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_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) */ }
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