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