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- /* 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"
- #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 (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
- pr_info("\tRCU strict (and thus non-scalable) grace periods 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 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 (!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.)
- */
- if (blkd_state & RCU_EXP_BLKD && rdp->exp_deferred_qs)
- rcu_report_exp_rdp(rdp);
- else
- WARN_ON_ONCE(rdp->exp_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_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_ON_ONCE(!preempt && rcu_preempt_depth() > 0);
- 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((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 {
- 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->exp_deferred_qs)
- 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)
- {
- current->rcu_read_lock_nesting++;
- }
- static int rcu_preempt_read_exit(void)
- {
- return --current->rcu_read_lock_nesting;
- }
- static void rcu_preempt_depth_set(int val)
- {
- 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;
- if (rcu_preempt_read_exit() == 0) {
- barrier(); /* critical section before exit code. */
- 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 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->exp_deferred_qs) {
- 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)) {
- 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->exp_deferred_qs)
- 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) == 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);
- } 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.exp_deferred_qs) ||
- 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.
- */
- static 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 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) {
- bool exp;
- struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
- struct rcu_node *rnp = rdp->mynode;
- exp = (t->rcu_blocked_node &&
- READ_ONCE(t->rcu_blocked_node->exp_tasks)) ||
- (rdp->grpmask & READ_ONCE(rnp->expmask));
- // Need to defer quiescent state until everything is enabled.
- if (use_softirq && (in_irq() || (exp && !irqs_were_disabled))) {
- // Using softirq, safe to awaken, and either the
- // wakeup is free or there is an expedited GP.
- raise_softirq_irqoff(RCU_SOFTIRQ);
- } else {
- // Enabling BH or preempt does reschedule, so...
- // Also if no expediting, 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 &&
- !rdp->defer_qs_iw_pending && exp && cpu_online(rdp->cpu)) {
- // Get scheduler to re-evaluate and call hooks.
- // If !IRQ_WORK, FQS scan will eventually IPI.
- 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 (user || rcu_is_cpu_rrupt_from_idle()) {
- rcu_note_voluntary_context_switch(current);
- }
- 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;
- 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)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);
- 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 */
- /*
- * 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 (!IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ||
- irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)
- return;
- rdp = this_cpu_ptr(&rcu_data);
- 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))
- 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.
- */
- 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);
- 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();
- rcu_tasks_qs(current, preempt);
- out:
- 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 bool rcu_preempt_need_deferred_qs(struct task_struct *t)
- {
- return false;
- }
- static void rcu_preempt_deferred_qs(struct task_struct *t) { }
- /*
- * 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)
- {
- #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 */
- }
- #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, 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 (;;) {
- 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 (!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 &&
- (!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld))) {
- 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);
- }
- }
- /*
- * 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_data.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 void 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;
- if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
- return;
- rcu_state.boost = 1;
- if (rnp->boost_kthread_task != NULL)
- 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. */
- }
- /*
- * 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);
- }
- /*
- * Spawn boost kthreads -- called as soon as the scheduler is running.
- */
- static void __init rcu_spawn_boost_kthreads(void)
- {
- struct rcu_node *rnp;
- rcu_for_each_leaf_node(rnp)
- 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)
- 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 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 non-offloaded 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_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
- !rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist);
- }
- /*
- * 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)
- {
- }
- #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.
- *
- * The following preprocessor symbol controls this:
- *
- * 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!
- *
- * The value below works 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. */
- static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
- module_param(rcu_idle_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 about what to set the timeout.
- *
- * 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();
- /* If no non-offloaded callbacks, RCU doesn't need the CPU. */
- if (rcu_segcblist_empty(&rdp->cblist) ||
- rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist)) {
- *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 and round. */
- dj = round_up(rcu_idle_gp_delay + jiffies, rcu_idle_gp_delay) - 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 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_segcblist_is_offloaded(&rdp->cblist))
- return;
- /* Handle nohz enablement switches conservatively. */
- tne = READ_ONCE(tick_nohz_active);
- if (tne != rdp->tick_nohz_enabled_snap) {
- if (!rcu_segcblist_empty(&rdp->cblist))
- invoke_rcu_core(); /* force nohz to see update. */
- rdp->tick_nohz_enabled_snap = tne;
- return;
- }
- if (!tne)
- 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)
- {
- struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
- lockdep_assert_irqs_disabled();
- if (rcu_segcblist_is_offloaded(&rdp->cblist))
- return;
- if (rcu_try_advance_all_cbs())
- invoke_rcu_core();
- }
- #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
- #ifdef CONFIG_RCU_NOCB_CPU
- /*
- * Offload callback processing from the boot-time-specified set of CPUs
- * specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads
- * created that pull the callbacks from the corresponding CPU, wait for
- * a grace period to elapse, and invoke the callbacks. These kthreads
- * are organized into GP kthreads, which manage incoming callbacks, wait for
- * grace periods, and awaken CB kthreads, and the CB kthreads, which only
- * invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs
- * do a wake_up() on their GP 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 callbacks can also 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.
- * The string after the "rcu_nocbs=" is either "all" for all CPUs, or a
- * comma-separated list of CPUs and/or CPU ranges. If an invalid list is
- * given, a warning is emitted and all CPUs are offloaded.
- */
- static int __init rcu_nocb_setup(char *str)
- {
- alloc_bootmem_cpumask_var(&rcu_nocb_mask);
- if (!strcasecmp(str, "all"))
- cpumask_setall(rcu_nocb_mask);
- else
- if (cpulist_parse(str, rcu_nocb_mask)) {
- pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
- cpumask_setall(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);
- /*
- * Don't bother bypassing ->cblist if the call_rcu() rate is low.
- * After all, the main point of bypassing is to avoid lock contention
- * on ->nocb_lock, which only can happen at high call_rcu() rates.
- */
- int nocb_nobypass_lim_per_jiffy = 16 * 1000 / HZ;
- module_param(nocb_nobypass_lim_per_jiffy, int, 0);
- /*
- * Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the
- * lock isn't immediately available, increment ->nocb_lock_contended to
- * flag the contention.
- */
- static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
- __acquires(&rdp->nocb_bypass_lock)
- {
- lockdep_assert_irqs_disabled();
- if (raw_spin_trylock(&rdp->nocb_bypass_lock))
- return;
- atomic_inc(&rdp->nocb_lock_contended);
- WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
- smp_mb__after_atomic(); /* atomic_inc() before lock. */
- raw_spin_lock(&rdp->nocb_bypass_lock);
- smp_mb__before_atomic(); /* atomic_dec() after lock. */
- atomic_dec(&rdp->nocb_lock_contended);
- }
- /*
- * Spinwait until the specified rcu_data structure's ->nocb_lock is
- * not contended. Please note that this is extremely special-purpose,
- * relying on the fact that at most two kthreads and one CPU contend for
- * this lock, and also that the two kthreads are guaranteed to have frequent
- * grace-period-duration time intervals between successive acquisitions
- * of the lock. This allows us to use an extremely simple throttling
- * mechanism, and further to apply it only to the CPU doing floods of
- * call_rcu() invocations. Don't try this at home!
- */
- static void rcu_nocb_wait_contended(struct rcu_data *rdp)
- {
- WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
- while (WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)))
- cpu_relax();
- }
- /*
- * Conditionally acquire the specified rcu_data structure's
- * ->nocb_bypass_lock.
- */
- static bool rcu_nocb_bypass_trylock(struct rcu_data *rdp)
- {
- lockdep_assert_irqs_disabled();
- return raw_spin_trylock(&rdp->nocb_bypass_lock);
- }
- /*
- * Release the specified rcu_data structure's ->nocb_bypass_lock.
- */
- static void rcu_nocb_bypass_unlock(struct rcu_data *rdp)
- __releases(&rdp->nocb_bypass_lock)
- {
- lockdep_assert_irqs_disabled();
- raw_spin_unlock(&rdp->nocb_bypass_lock);
- }
- /*
- * Acquire the specified rcu_data structure's ->nocb_lock, but only
- * if it corresponds to a no-CBs CPU.
- */
- static void rcu_nocb_lock(struct rcu_data *rdp)
- {
- lockdep_assert_irqs_disabled();
- if (!rcu_segcblist_is_offloaded(&rdp->cblist))
- return;
- raw_spin_lock(&rdp->nocb_lock);
- }
- /*
- * Release the specified rcu_data structure's ->nocb_lock, but only
- * if it corresponds to a no-CBs CPU.
- */
- static void rcu_nocb_unlock(struct rcu_data *rdp)
- {
- if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
- lockdep_assert_irqs_disabled();
- raw_spin_unlock(&rdp->nocb_lock);
- }
- }
- /*
- * Release the specified rcu_data structure's ->nocb_lock and restore
- * interrupts, but only if it corresponds to a no-CBs CPU.
- */
- static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
- unsigned long flags)
- {
- if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
- lockdep_assert_irqs_disabled();
- raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
- } else {
- local_irq_restore(flags);
- }
- }
- /* Lockdep check that ->cblist may be safely accessed. */
- static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
- {
- lockdep_assert_irqs_disabled();
- if (rcu_segcblist_is_offloaded(&rdp->cblist))
- lockdep_assert_held(&rdp->nocb_lock);
- }
- /*
- * 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 GP kthread for this NOCB group. Caller holds ->nocb_lock
- * and this function releases it.
- */
- static void wake_nocb_gp(struct rcu_data *rdp, bool force,
- unsigned long flags)
- __releases(rdp->nocb_lock)
- {
- bool needwake = false;
- struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
- lockdep_assert_held(&rdp->nocb_lock);
- if (!READ_ONCE(rdp_gp->nocb_gp_kthread)) {
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
- TPS("AlreadyAwake"));
- rcu_nocb_unlock_irqrestore(rdp, flags);
- return;
- }
- if (READ_ONCE(rdp->nocb_defer_wakeup) > RCU_NOCB_WAKE_NOT) {
- WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
- del_timer(&rdp->nocb_timer);
- }
- rcu_nocb_unlock_irqrestore(rdp, flags);
- raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
- if (force || READ_ONCE(rdp_gp->nocb_gp_sleep)) {
- WRITE_ONCE(rdp_gp->nocb_gp_sleep, false);
- needwake = true;
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DoWake"));
- }
- raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
- if (needwake)
- wake_up_process(rdp_gp->nocb_gp_kthread);
- }
- /*
- * Arrange to wake the GP kthread for this NOCB group at some future
- * time when it is safe to do so.
- */
- static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
- const char *reason)
- {
- if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
- mod_timer(&rdp->nocb_timer, jiffies + 1);
- if (rdp->nocb_defer_wakeup < waketype)
- WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
- }
- /*
- * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
- * However, if there is a callback to be enqueued and if ->nocb_bypass
- * proves to be initially empty, just return false because the no-CB GP
- * kthread may need to be awakened in this case.
- *
- * Note that this function always returns true if rhp is NULL.
- */
- static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
- unsigned long j)
- {
- struct rcu_cblist rcl;
- WARN_ON_ONCE(!rcu_segcblist_is_offloaded(&rdp->cblist));
- rcu_lockdep_assert_cblist_protected(rdp);
- lockdep_assert_held(&rdp->nocb_bypass_lock);
- if (rhp && !rcu_cblist_n_cbs(&rdp->nocb_bypass)) {
- raw_spin_unlock(&rdp->nocb_bypass_lock);
- return false;
- }
- /* Note: ->cblist.len already accounts for ->nocb_bypass contents. */
- if (rhp)
- rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
- rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
- rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
- WRITE_ONCE(rdp->nocb_bypass_first, j);
- rcu_nocb_bypass_unlock(rdp);
- return true;
- }
- /*
- * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
- * However, if there is a callback to be enqueued and if ->nocb_bypass
- * proves to be initially empty, just return false because the no-CB GP
- * kthread may need to be awakened in this case.
- *
- * Note that this function always returns true if rhp is NULL.
- */
- static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
- unsigned long j)
- {
- if (!rcu_segcblist_is_offloaded(&rdp->cblist))
- return true;
- rcu_lockdep_assert_cblist_protected(rdp);
- rcu_nocb_bypass_lock(rdp);
- return rcu_nocb_do_flush_bypass(rdp, rhp, j);
- }
- /*
- * If the ->nocb_bypass_lock is immediately available, flush the
- * ->nocb_bypass queue into ->cblist.
- */
- static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j)
- {
- rcu_lockdep_assert_cblist_protected(rdp);
- if (!rcu_segcblist_is_offloaded(&rdp->cblist) ||
- !rcu_nocb_bypass_trylock(rdp))
- return;
- WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j));
- }
- /*
- * See whether it is appropriate to use the ->nocb_bypass list in order
- * to control contention on ->nocb_lock. A limited number of direct
- * enqueues are permitted into ->cblist per jiffy. If ->nocb_bypass
- * is non-empty, further callbacks must be placed into ->nocb_bypass,
- * otherwise rcu_barrier() breaks. Use rcu_nocb_flush_bypass() to switch
- * back to direct use of ->cblist. However, ->nocb_bypass should not be
- * used if ->cblist is empty, because otherwise callbacks can be stranded
- * on ->nocb_bypass because we cannot count on the current CPU ever again
- * invoking call_rcu(). The general rule is that if ->nocb_bypass is
- * non-empty, the corresponding no-CBs grace-period kthread must not be
- * in an indefinite sleep state.
- *
- * Finally, it is not permitted to use the bypass during early boot,
- * as doing so would confuse the auto-initialization code. Besides
- * which, there is no point in worrying about lock contention while
- * there is only one CPU in operation.
- */
- static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
- bool *was_alldone, unsigned long flags)
- {
- unsigned long c;
- unsigned long cur_gp_seq;
- unsigned long j = jiffies;
- long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
- if (!rcu_segcblist_is_offloaded(&rdp->cblist)) {
- *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
- return false; /* Not offloaded, no bypassing. */
- }
- lockdep_assert_irqs_disabled();
- // Don't use ->nocb_bypass during early boot.
- if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) {
- rcu_nocb_lock(rdp);
- WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
- *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
- return false;
- }
- // If we have advanced to a new jiffy, reset counts to allow
- // moving back from ->nocb_bypass to ->cblist.
- if (j == rdp->nocb_nobypass_last) {
- c = rdp->nocb_nobypass_count + 1;
- } else {
- WRITE_ONCE(rdp->nocb_nobypass_last, j);
- c = rdp->nocb_nobypass_count - nocb_nobypass_lim_per_jiffy;
- if (ULONG_CMP_LT(rdp->nocb_nobypass_count,
- nocb_nobypass_lim_per_jiffy))
- c = 0;
- else if (c > nocb_nobypass_lim_per_jiffy)
- c = nocb_nobypass_lim_per_jiffy;
- }
- WRITE_ONCE(rdp->nocb_nobypass_count, c);
- // If there hasn't yet been all that many ->cblist enqueues
- // this jiffy, tell the caller to enqueue onto ->cblist. But flush
- // ->nocb_bypass first.
- if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy) {
- rcu_nocb_lock(rdp);
- *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
- if (*was_alldone)
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
- TPS("FirstQ"));
- WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j));
- WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
- return false; // Caller must enqueue the callback.
- }
- // If ->nocb_bypass has been used too long or is too full,
- // flush ->nocb_bypass to ->cblist.
- if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) ||
- ncbs >= qhimark) {
- rcu_nocb_lock(rdp);
- if (!rcu_nocb_flush_bypass(rdp, rhp, j)) {
- *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
- if (*was_alldone)
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
- TPS("FirstQ"));
- WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
- return false; // Caller must enqueue the callback.
- }
- if (j != rdp->nocb_gp_adv_time &&
- rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
- rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
- rcu_advance_cbs_nowake(rdp->mynode, rdp);
- rdp->nocb_gp_adv_time = j;
- }
- rcu_nocb_unlock_irqrestore(rdp, flags);
- return true; // Callback already enqueued.
- }
- // We need to use the bypass.
- rcu_nocb_wait_contended(rdp);
- rcu_nocb_bypass_lock(rdp);
- ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
- rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
- rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
- if (!ncbs) {
- WRITE_ONCE(rdp->nocb_bypass_first, j);
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ"));
- }
- rcu_nocb_bypass_unlock(rdp);
- smp_mb(); /* Order enqueue before wake. */
- if (ncbs) {
- local_irq_restore(flags);
- } else {
- // No-CBs GP kthread might be indefinitely asleep, if so, wake.
- rcu_nocb_lock(rdp); // Rare during call_rcu() flood.
- if (!rcu_segcblist_pend_cbs(&rdp->cblist)) {
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
- TPS("FirstBQwake"));
- __call_rcu_nocb_wake(rdp, true, flags);
- } else {
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
- TPS("FirstBQnoWake"));
- rcu_nocb_unlock_irqrestore(rdp, flags);
- }
- }
- return true; // Callback already enqueued.
- }
- /*
- * Awaken the no-CBs grace-period kthead if needed, either due to it
- * legitimately being asleep or due to overload conditions.
- *
- * If warranted, also wake up the kthread servicing this CPUs queues.
- */
- static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
- unsigned long flags)
- __releases(rdp->nocb_lock)
- {
- unsigned long cur_gp_seq;
- unsigned long j;
- long len;
- struct task_struct *t;
- // If we are being polled or there is no kthread, just leave.
- t = READ_ONCE(rdp->nocb_gp_kthread);
- if (rcu_nocb_poll || !t) {
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
- TPS("WakeNotPoll"));
- rcu_nocb_unlock_irqrestore(rdp, flags);
- return;
- }
- // Need to actually to a wakeup.
- len = rcu_segcblist_n_cbs(&rdp->cblist);
- if (was_alldone) {
- rdp->qlen_last_fqs_check = len;
- if (!irqs_disabled_flags(flags)) {
- /* ... if queue was empty ... */
- wake_nocb_gp(rdp, false, flags);
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
- TPS("WakeEmpty"));
- } else {
- wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
- TPS("WakeEmptyIsDeferred"));
- rcu_nocb_unlock_irqrestore(rdp, flags);
- }
- } else if (len > rdp->qlen_last_fqs_check + qhimark) {
- /* ... or if many callbacks queued. */
- rdp->qlen_last_fqs_check = len;
- j = jiffies;
- if (j != rdp->nocb_gp_adv_time &&
- rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
- rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
- rcu_advance_cbs_nowake(rdp->mynode, rdp);
- rdp->nocb_gp_adv_time = j;
- }
- smp_mb(); /* Enqueue before timer_pending(). */
- if ((rdp->nocb_cb_sleep ||
- !rcu_segcblist_ready_cbs(&rdp->cblist)) &&
- !timer_pending(&rdp->nocb_bypass_timer))
- wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
- TPS("WakeOvfIsDeferred"));
- rcu_nocb_unlock_irqrestore(rdp, flags);
- } else {
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
- rcu_nocb_unlock_irqrestore(rdp, flags);
- }
- return;
- }
- /* Wake up the no-CBs GP kthread to flush ->nocb_bypass. */
- static void do_nocb_bypass_wakeup_timer(struct timer_list *t)
- {
- unsigned long flags;
- struct rcu_data *rdp = from_timer(rdp, t, nocb_bypass_timer);
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Timer"));
- rcu_nocb_lock_irqsave(rdp, flags);
- smp_mb__after_spinlock(); /* Timer expire before wakeup. */
- __call_rcu_nocb_wake(rdp, true, flags);
- }
- /*
- * No-CBs GP kthreads come here to wait for additional callbacks to show up
- * or for grace periods to end.
- */
- static void nocb_gp_wait(struct rcu_data *my_rdp)
- {
- bool bypass = false;
- long bypass_ncbs;
- int __maybe_unused cpu = my_rdp->cpu;
- unsigned long cur_gp_seq;
- unsigned long flags;
- bool gotcbs = false;
- unsigned long j = jiffies;
- bool needwait_gp = false; // This prevents actual uninitialized use.
- bool needwake;
- bool needwake_gp;
- struct rcu_data *rdp;
- struct rcu_node *rnp;
- unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
- bool wasempty = false;
- /*
- * Each pass through the following loop checks for CBs and for the
- * nearest grace period (if any) to wait for next. The CB kthreads
- * and the global grace-period kthread are awakened if needed.
- */
- WARN_ON_ONCE(my_rdp->nocb_gp_rdp != my_rdp);
- for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) {
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
- rcu_nocb_lock_irqsave(rdp, flags);
- bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
- if (bypass_ncbs &&
- (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
- bypass_ncbs > 2 * qhimark)) {
- // Bypass full or old, so flush it.
- (void)rcu_nocb_try_flush_bypass(rdp, j);
- bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
- } else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) {
- rcu_nocb_unlock_irqrestore(rdp, flags);
- continue; /* No callbacks here, try next. */
- }
- if (bypass_ncbs) {
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
- TPS("Bypass"));
- bypass = true;
- }
- rnp = rdp->mynode;
- if (bypass) { // Avoid race with first bypass CB.
- WRITE_ONCE(my_rdp->nocb_defer_wakeup,
- RCU_NOCB_WAKE_NOT);
- del_timer(&my_rdp->nocb_timer);
- }
- // Advance callbacks if helpful and low contention.
- needwake_gp = false;
- if (!rcu_segcblist_restempty(&rdp->cblist,
- RCU_NEXT_READY_TAIL) ||
- (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
- rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) {
- raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
- needwake_gp = rcu_advance_cbs(rnp, rdp);
- wasempty = rcu_segcblist_restempty(&rdp->cblist,
- RCU_NEXT_READY_TAIL);
- raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */
- }
- // Need to wait on some grace period?
- WARN_ON_ONCE(wasempty &&
- !rcu_segcblist_restempty(&rdp->cblist,
- RCU_NEXT_READY_TAIL));
- if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) {
- if (!needwait_gp ||
- ULONG_CMP_LT(cur_gp_seq, wait_gp_seq))
- wait_gp_seq = cur_gp_seq;
- needwait_gp = true;
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
- TPS("NeedWaitGP"));
- }
- if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
- needwake = rdp->nocb_cb_sleep;
- WRITE_ONCE(rdp->nocb_cb_sleep, false);
- smp_mb(); /* CB invocation -after- GP end. */
- } else {
- needwake = false;
- }
- rcu_nocb_unlock_irqrestore(rdp, flags);
- if (needwake) {
- swake_up_one(&rdp->nocb_cb_wq);
- gotcbs = true;
- }
- if (needwake_gp)
- rcu_gp_kthread_wake();
- }
- my_rdp->nocb_gp_bypass = bypass;
- my_rdp->nocb_gp_gp = needwait_gp;
- my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
- if (bypass && !rcu_nocb_poll) {
- // At least one child with non-empty ->nocb_bypass, so set
- // timer in order to avoid stranding its callbacks.
- raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
- mod_timer(&my_rdp->nocb_bypass_timer, j + 2);
- raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
- }
- if (rcu_nocb_poll) {
- /* Polling, so trace if first poll in the series. */
- if (gotcbs)
- trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
- schedule_timeout_idle(1);
- } else if (!needwait_gp) {
- /* Wait for callbacks to appear. */
- trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
- swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
- !READ_ONCE(my_rdp->nocb_gp_sleep));
- trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep"));
- } else {
- rnp = my_rdp->mynode;
- trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait"));
- swait_event_interruptible_exclusive(
- rnp->nocb_gp_wq[rcu_seq_ctr(wait_gp_seq) & 0x1],
- rcu_seq_done(&rnp->gp_seq, wait_gp_seq) ||
- !READ_ONCE(my_rdp->nocb_gp_sleep));
- trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("EndWait"));
- }
- if (!rcu_nocb_poll) {
- raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
- if (bypass)
- del_timer(&my_rdp->nocb_bypass_timer);
- WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
- raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
- }
- my_rdp->nocb_gp_seq = -1;
- WARN_ON(signal_pending(current));
- }
- /*
- * No-CBs grace-period-wait kthread. There is one of these per group
- * of CPUs, but only once at least one CPU in that group has come online
- * at least once since boot. This kthread checks for newly posted
- * callbacks from any of the CPUs it is responsible for, waits for a
- * grace period, then awakens all of the rcu_nocb_cb_kthread() instances
- * that then have callback-invocation work to do.
- */
- static int rcu_nocb_gp_kthread(void *arg)
- {
- struct rcu_data *rdp = arg;
- for (;;) {
- WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);
- nocb_gp_wait(rdp);
- cond_resched_tasks_rcu_qs();
- }
- return 0;
- }
- /*
- * Invoke any ready callbacks from the corresponding no-CBs CPU,
- * then, if there are no more, wait for more to appear.
- */
- static void nocb_cb_wait(struct rcu_data *rdp)
- {
- unsigned long cur_gp_seq;
- unsigned long flags;
- bool needwake_gp = false;
- struct rcu_node *rnp = rdp->mynode;
- local_irq_save(flags);
- rcu_momentary_dyntick_idle();
- local_irq_restore(flags);
- local_bh_disable();
- rcu_do_batch(rdp);
- local_bh_enable();
- lockdep_assert_irqs_enabled();
- rcu_nocb_lock_irqsave(rdp, flags);
- if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
- rcu_seq_done(&rnp->gp_seq, cur_gp_seq) &&
- raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
- needwake_gp = rcu_advance_cbs(rdp->mynode, rdp);
- raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
- }
- if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
- rcu_nocb_unlock_irqrestore(rdp, flags);
- if (needwake_gp)
- rcu_gp_kthread_wake();
- return;
- }
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep"));
- WRITE_ONCE(rdp->nocb_cb_sleep, true);
- rcu_nocb_unlock_irqrestore(rdp, flags);
- if (needwake_gp)
- rcu_gp_kthread_wake();
- swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
- !READ_ONCE(rdp->nocb_cb_sleep));
- if (!smp_load_acquire(&rdp->nocb_cb_sleep)) { /* VVV */
- /* ^^^ Ensure CB invocation follows _sleep 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. Repeatedly invoke
- * nocb_cb_wait() to do the dirty work.
- */
- static int rcu_nocb_cb_kthread(void *arg)
- {
- struct rcu_data *rdp = arg;
- // Each pass through this loop does one callback batch, and,
- // if there are no more ready callbacks, waits for them.
- for (;;) {
- nocb_cb_wait(rdp);
- cond_resched_tasks_rcu_qs();
- }
- 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;
- rcu_nocb_lock_irqsave(rdp, flags);
- if (!rcu_nocb_need_deferred_wakeup(rdp)) {
- rcu_nocb_unlock_irqrestore(rdp, flags);
- return;
- }
- ndw = READ_ONCE(rdp->nocb_defer_wakeup);
- wake_nocb_gp(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 rcu_nocb_flush_deferred_wakeup(void)
- {
- do_nocb_deferred_wakeup(this_cpu_ptr(&rcu_data));
- }
- void __init rcu_init_nohz(void)
- {
- int cpu;
- bool need_rcu_nocb_mask = false;
- struct rcu_data *rdp;
- #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) {
- rdp = per_cpu_ptr(&rcu_data, cpu);
- if (rcu_segcblist_empty(&rdp->cblist))
- rcu_segcblist_init(&rdp->cblist);
- rcu_segcblist_offload(&rdp->cblist);
- }
- 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)
- {
- init_swait_queue_head(&rdp->nocb_cb_wq);
- init_swait_queue_head(&rdp->nocb_gp_wq);
- raw_spin_lock_init(&rdp->nocb_lock);
- raw_spin_lock_init(&rdp->nocb_bypass_lock);
- raw_spin_lock_init(&rdp->nocb_gp_lock);
- timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
- timer_setup(&rdp->nocb_bypass_timer, do_nocb_bypass_wakeup_timer, 0);
- rcu_cblist_init(&rdp->nocb_bypass);
- }
- /*
- * If the specified CPU is a no-CBs CPU that does not already have its
- * rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread
- * for this CPU's group has not yet been created, spawn it as well.
- */
- static void rcu_spawn_one_nocb_kthread(int cpu)
- {
- struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
- struct rcu_data *rdp_gp;
- 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->nocb_cb_kthread)
- return;
- /* If we didn't spawn the GP kthread first, reorganize! */
- rdp_gp = rdp->nocb_gp_rdp;
- if (!rdp_gp->nocb_gp_kthread) {
- t = kthread_run(rcu_nocb_gp_kthread, rdp_gp,
- "rcuog/%d", rdp_gp->cpu);
- if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__))
- return;
- WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
- }
- /* Spawn the kthread for this CPU. */
- t = kthread_run(rcu_nocb_cb_kthread, rdp,
- "rcuo%c/%d", rcu_state.abbr, cpu);
- if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))
- return;
- WRITE_ONCE(rdp->nocb_cb_kthread, t);
- WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
- }
- /*
- * If the specified CPU is a no-CBs CPU that does not already have its
- * rcuo kthread, spawn it.
- */
- static void rcu_spawn_cpu_nocb_kthread(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_cpu_nocb_kthread(cpu);
- }
- /* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
- static int rcu_nocb_gp_stride = -1;
- module_param(rcu_nocb_gp_stride, int, 0444);
- /*
- * Initialize GP-CB relationships for all no-CBs CPU.
- */
- static void __init rcu_organize_nocb_kthreads(void)
- {
- int cpu;
- bool firsttime = true;
- bool gotnocbs = false;
- bool gotnocbscbs = true;
- int ls = rcu_nocb_gp_stride;
- int nl = 0; /* Next GP kthread. */
- struct rcu_data *rdp;
- struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */
- struct rcu_data *rdp_prev = NULL;
- if (!cpumask_available(rcu_nocb_mask))
- return;
- if (ls == -1) {
- ls = nr_cpu_ids / int_sqrt(nr_cpu_ids);
- rcu_nocb_gp_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 GP kthread, set up for CBs & next GP. */
- gotnocbs = true;
- nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
- rdp->nocb_gp_rdp = rdp;
- rdp_gp = rdp;
- if (dump_tree) {
- if (!firsttime)
- pr_cont("%s\n", gotnocbscbs
- ? "" : " (self only)");
- gotnocbscbs = false;
- firsttime = false;
- pr_alert("%s: No-CB GP kthread CPU %d:",
- __func__, cpu);
- }
- } else {
- /* Another CB kthread, link to previous GP kthread. */
- gotnocbscbs = true;
- rdp->nocb_gp_rdp = rdp_gp;
- rdp_prev->nocb_next_cb_rdp = rdp;
- if (dump_tree)
- pr_cont(" %d", cpu);
- }
- rdp_prev = rdp;
- }
- if (gotnocbs && dump_tree)
- pr_cont("%s\n", gotnocbscbs ? "" : " (self only)");
- }
- /*
- * 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);
- /*
- * Dump out nocb grace-period kthread state for the specified rcu_data
- * structure.
- */
- static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
- {
- struct rcu_node *rnp = rdp->mynode;
- pr_info("nocb GP %d %c%c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu\n",
- rdp->cpu,
- "kK"[!!rdp->nocb_gp_kthread],
- "lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],
- "dD"[!!rdp->nocb_defer_wakeup],
- "tT"[timer_pending(&rdp->nocb_timer)],
- "bB"[timer_pending(&rdp->nocb_bypass_timer)],
- "sS"[!!rdp->nocb_gp_sleep],
- ".W"[swait_active(&rdp->nocb_gp_wq)],
- ".W"[swait_active(&rnp->nocb_gp_wq[0])],
- ".W"[swait_active(&rnp->nocb_gp_wq[1])],
- ".B"[!!rdp->nocb_gp_bypass],
- ".G"[!!rdp->nocb_gp_gp],
- (long)rdp->nocb_gp_seq,
- rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops));
- }
- /* Dump out nocb kthread state for the specified rcu_data structure. */
- static void show_rcu_nocb_state(struct rcu_data *rdp)
- {
- struct rcu_segcblist *rsclp = &rdp->cblist;
- bool waslocked;
- bool wastimer;
- bool wassleep;
- if (rdp->nocb_gp_rdp == rdp)
- show_rcu_nocb_gp_state(rdp);
- pr_info(" CB %d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%c%c%c q%ld\n",
- rdp->cpu, rdp->nocb_gp_rdp->cpu,
- "kK"[!!rdp->nocb_cb_kthread],
- "bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],
- "cC"[!!atomic_read(&rdp->nocb_lock_contended)],
- "lL"[raw_spin_is_locked(&rdp->nocb_lock)],
- "sS"[!!rdp->nocb_cb_sleep],
- ".W"[swait_active(&rdp->nocb_cb_wq)],
- jiffies - rdp->nocb_bypass_first,
- jiffies - rdp->nocb_nobypass_last,
- rdp->nocb_nobypass_count,
- ".D"[rcu_segcblist_ready_cbs(rsclp)],
- ".W"[!rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)],
- ".R"[!rcu_segcblist_restempty(rsclp, RCU_WAIT_TAIL)],
- ".N"[!rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL)],
- ".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
- rcu_segcblist_n_cbs(&rdp->cblist));
- /* It is OK for GP kthreads to have GP state. */
- if (rdp->nocb_gp_rdp == rdp)
- return;
- waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);
- wastimer = timer_pending(&rdp->nocb_bypass_timer);
- wassleep = swait_active(&rdp->nocb_gp_wq);
- if (!rdp->nocb_gp_sleep && !waslocked && !wastimer && !wassleep)
- return; /* Nothing untowards. */
- pr_info(" nocb GP activity on CB-only CPU!!! %c%c%c%c %c\n",
- "lL"[waslocked],
- "dD"[!!rdp->nocb_defer_wakeup],
- "tT"[wastimer],
- "sS"[!!rdp->nocb_gp_sleep],
- ".W"[wassleep]);
- }
- #else /* #ifdef CONFIG_RCU_NOCB_CPU */
- /* No ->nocb_lock to acquire. */
- static void rcu_nocb_lock(struct rcu_data *rdp)
- {
- }
- /* No ->nocb_lock to release. */
- static void rcu_nocb_unlock(struct rcu_data *rdp)
- {
- }
- /* No ->nocb_lock to release. */
- static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
- unsigned long flags)
- {
- local_irq_restore(flags);
- }
- /* Lockdep check that ->cblist may be safely accessed. */
- static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
- {
- lockdep_assert_irqs_disabled();
- }
- 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 rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
- unsigned long j)
- {
- return true;
- }
- static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
- bool *was_alldone, unsigned long flags)
- {
- return false;
- }
- static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
- unsigned long flags)
- {
- WARN_ON_ONCE(1); /* Should be dead code! */
- }
- 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_cpu_nocb_kthread(int cpu)
- {
- }
- static void __init rcu_spawn_nocb_kthreads(void)
- {
- }
- static void show_rcu_nocb_state(struct rcu_data *rdp)
- {
- }
- #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() ||
- 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_FLAG_RCU);
- }
- /* Record the current task on dyntick-idle entry. */
- static __always_inline 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 __always_inline 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) */
- }
- /* Turn on heavyweight RCU tasks trace readers on idle/user entry. */
- static __always_inline void rcu_dynticks_task_trace_enter(void)
- {
- #ifdef CONFIG_TASKS_TRACE_RCU
- if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
- current->trc_reader_special.b.need_mb = true;
- #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
- }
- /* Turn off heavyweight RCU tasks trace readers on idle/user exit. */
- static __always_inline void rcu_dynticks_task_trace_exit(void)
- {
- #ifdef CONFIG_TASKS_TRACE_RCU
- if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
- current->trc_reader_special.b.need_mb = false;
- #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
- }
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