--- /dev/null
+/*
+ * Read-Copy Update mechanism for mutual exclusion (tree-based version)
+ * Internal non-public definitions that provide either classic
+ * or preemptible semantics.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright Red Hat, 2009
+ * Copyright IBM Corporation, 2009
+ *
+ * Author: Ingo Molnar <mingo@elte.hu>
+ * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ */
+
+#ifdef CONFIG_RCU_BOOST
+
+#include "../locking/rtmutex_common.h"
+
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+/*
+ * Control variables for per-CPU and per-rcu_node kthreads. These
+ * handle all flavors of RCU.
+ */
+DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
+DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
+DEFINE_PER_CPU(char, rcu_cpu_has_work);
+
+#ifdef CONFIG_RCU_NOCB_CPU
+static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
+static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */
+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. If you like #ifdef, you
+ * will love this function.
+ */
+static void __init rcu_bootup_announce_oddness(void)
+{
+ if (IS_ENABLED(CONFIG_RCU_TRACE))
+ pr_info("\tRCU debugfs-based tracing is enabled.\n");
+ if ((IS_ENABLED(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) ||
+ (!IS_ENABLED(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32))
+ pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
+ CONFIG_RCU_FANOUT);
+ if (IS_ENABLED(CONFIG_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_TORTURE_TEST_RUNNABLE))
+ pr_info("\tRCU torture testing starts during boot.\n");
+ if (IS_ENABLED(CONFIG_RCU_CPU_STALL_INFO))
+ pr_info("\tAdditional per-CPU info printed with stalls.\n");
+ if (NUM_RCU_LVL_4 != 0)
+ pr_info("\tFour-level hierarchy is enabled.\n");
+ if (CONFIG_RCU_FANOUT_LEAF != 16)
+ pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
+ CONFIG_RCU_FANOUT_LEAF);
+ if (rcu_fanout_leaf != CONFIG_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=%d.\n", NR_CPUS, nr_cpu_ids);
+ if (IS_ENABLED(CONFIG_RCU_BOOST))
+ pr_info("\tRCU kthread priority: %d.\n", kthread_prio);
+}
+
+#ifdef CONFIG_PREEMPT_RCU
+
+RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
+static struct rcu_state *rcu_state_p = &rcu_preempt_state;
+
+static int rcu_preempted_readers_exp(struct rcu_node *rnp);
+static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
+ bool wake);
+
+/*
+ * 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();
+}
+
+/*
+ * Record a preemptible-RCU quiescent state for the specified CPU. Note
+ * that this just means that the task currently running on the CPU is
+ * not in a quiescent state. There might be any number of tasks blocked
+ * while in an RCU read-side critical section.
+ *
+ * As with the other rcu_*_qs() functions, callers to this function
+ * must disable preemption.
+ */
+static void rcu_preempt_qs(void)
+{
+ if (!__this_cpu_read(rcu_preempt_data.passed_quiesce)) {
+ trace_rcu_grace_period(TPS("rcu_preempt"),
+ __this_cpu_read(rcu_preempt_data.gpnum),
+ TPS("cpuqs"));
+ __this_cpu_write(rcu_preempt_data.passed_quiesce, 1);
+ barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
+ current->rcu_read_unlock_special.b.need_qs = false;
+ }
+}
+
+/*
+ * We have entered the scheduler, and the current task might soon be
+ * context-switched away from. If this task is in an RCU read-side
+ * critical section, we will no longer be able to rely on the CPU to
+ * record that fact, so we enqueue the task on the blkd_tasks list.
+ * The task will dequeue itself when it exits the outermost enclosing
+ * RCU read-side critical section. Therefore, the current grace period
+ * cannot be permitted to complete until the blkd_tasks list entries
+ * predating the current grace period drain, in other words, until
+ * rnp->gp_tasks becomes NULL.
+ *
+ * Caller must disable preemption.
+ */
+static void rcu_preempt_note_context_switch(void)
+{
+ struct task_struct *t = current;
+ unsigned long flags;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+
+ if (t->rcu_read_lock_nesting > 0 &&
+ !t->rcu_read_unlock_special.b.blocked) {
+
+ /* Possibly blocking in an RCU read-side critical section. */
+ rdp = this_cpu_ptr(rcu_preempt_state.rda);
+ rnp = rdp->mynode;
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ smp_mb__after_unlock_lock();
+ t->rcu_read_unlock_special.b.blocked = true;
+ t->rcu_blocked_node = rnp;
+
+ /*
+ * If this CPU has already checked in, then this task
+ * will hold up the next grace period rather than the
+ * current grace period. Queue the task accordingly.
+ * If the task is queued for the current grace period
+ * (i.e., this CPU has not yet passed through a quiescent
+ * state for the current grace period), then as long
+ * as that task remains queued, the current grace period
+ * cannot end. Note that there is some uncertainty as
+ * to exactly when the current grace period started.
+ * We take a conservative approach, which can result
+ * in unnecessarily waiting on tasks that started very
+ * slightly after the current grace period began. C'est
+ * la vie!!!
+ *
+ * But first, note that the current CPU must still be
+ * on line!
+ */
+ WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
+ WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
+ if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
+ list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
+ rnp->gp_tasks = &t->rcu_node_entry;
+#ifdef CONFIG_RCU_BOOST
+ if (rnp->boost_tasks != NULL)
+ rnp->boost_tasks = rnp->gp_tasks;
+#endif /* #ifdef CONFIG_RCU_BOOST */
+ } else {
+ list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
+ if (rnp->qsmask & rdp->grpmask)
+ rnp->gp_tasks = &t->rcu_node_entry;
+ }
+ trace_rcu_preempt_task(rdp->rsp->name,
+ t->pid,
+ (rnp->qsmask & rdp->grpmask)
+ ? rnp->gpnum
+ : rnp->gpnum + 1);
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ } else if (t->rcu_read_lock_nesting < 0 &&
+ t->rcu_read_unlock_special.s) {
+
+ /*
+ * Complete exit from RCU read-side critical section on
+ * behalf of preempted instance of __rcu_read_unlock().
+ */
+ rcu_read_unlock_special(t);
+ }
+
+ /*
+ * 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_preempt_qs();
+}
+
+/*
+ * Check for preempted RCU readers blocking the current grace period
+ * for the specified rcu_node structure. If the caller needs a reliable
+ * answer, it must hold the rcu_node's ->lock.
+ */
+static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
+{
+ return rnp->gp_tasks != NULL;
+}
+
+/*
+ * 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);
+}
+
+/*
+ * 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.
+ */
+void rcu_read_unlock_special(struct task_struct *t)
+{
+ bool empty_exp;
+ bool empty_norm;
+ bool empty_exp_now;
+ unsigned long flags;
+ struct list_head *np;
+#ifdef CONFIG_RCU_BOOST
+ bool drop_boost_mutex = false;
+#endif /* #ifdef CONFIG_RCU_BOOST */
+ struct rcu_node *rnp;
+ union rcu_special special;
+
+ /* NMI handlers cannot block and cannot safely manipulate state. */
+ if (in_nmi())
+ return;
+
+ local_irq_save(flags);
+
+ /*
+ * If RCU core is waiting for this CPU to exit critical section,
+ * let it know that we have done so. Because irqs are disabled,
+ * t->rcu_read_unlock_special cannot change.
+ */
+ special = t->rcu_read_unlock_special;
+ if (special.b.need_qs) {
+ rcu_preempt_qs();
+ t->rcu_read_unlock_special.b.need_qs = false;
+ if (!t->rcu_read_unlock_special.s) {
+ local_irq_restore(flags);
+ return;
+ }
+ }
+
+ /* Hardware IRQ handlers cannot block, complain if they get here. */
+ if (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET)) {
+ lockdep_rcu_suspicious(__FILE__, __LINE__,
+ "rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n");
+ pr_alert("->rcu_read_unlock_special: %#x (b: %d, nq: %d)\n",
+ t->rcu_read_unlock_special.s,
+ t->rcu_read_unlock_special.b.blocked,
+ t->rcu_read_unlock_special.b.need_qs);
+ local_irq_restore(flags);
+ return;
+ }
+
+ /* Clean up if blocked during RCU read-side critical section. */
+ if (special.b.blocked) {
+ t->rcu_read_unlock_special.b.blocked = false;
+
+ /*
+ * Remove this task from the list it blocked on. The
+ * task can migrate while we acquire the lock, but at
+ * most one time. So at most two passes through loop.
+ */
+ for (;;) {
+ rnp = t->rcu_blocked_node;
+ raw_spin_lock(&rnp->lock); /* irqs already disabled. */
+ smp_mb__after_unlock_lock();
+ if (rnp == t->rcu_blocked_node)
+ break;
+ raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
+ }
+ empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
+ empty_exp = !rcu_preempted_readers_exp(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->gpnum, t->pid);
+ if (&t->rcu_node_entry == rnp->gp_tasks)
+ rnp->gp_tasks = np;
+ if (&t->rcu_node_entry == rnp->exp_tasks)
+ rnp->exp_tasks = np;
+#ifdef CONFIG_RCU_BOOST
+ if (&t->rcu_node_entry == rnp->boost_tasks)
+ rnp->boost_tasks = np;
+ /* Snapshot ->boost_mtx ownership with rcu_node lock held. */
+ drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+ /*
+ * 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 = !rcu_preempted_readers_exp(rnp);
+ if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
+ trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
+ rnp->gpnum,
+ 0, rnp->qsmask,
+ rnp->level,
+ rnp->grplo,
+ rnp->grphi,
+ !!rnp->gp_tasks);
+ rcu_report_unblock_qs_rnp(&rcu_preempt_state,
+ rnp, flags);
+ } else {
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ }
+
+#ifdef CONFIG_RCU_BOOST
+ /* Unboost if we were boosted. */
+ if (drop_boost_mutex)
+ rt_mutex_unlock(&rnp->boost_mtx);
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+ /*
+ * 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(&rcu_preempt_state, rnp, true);
+ } else {
+ local_irq_restore(flags);
+ }
+}
+
+/*
+ * Dump detailed information for all tasks blocking the current RCU
+ * grace period on the specified rcu_node structure.
+ */
+static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
+{
+ unsigned long flags;
+ struct task_struct *t;
+
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ if (!rcu_preempt_blocked_readers_cgp(rnp)) {
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ return;
+ }
+ t = list_entry(rnp->gp_tasks,
+ struct task_struct, rcu_node_entry);
+ list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
+ sched_show_task(t);
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
+/*
+ * Dump detailed information for all tasks blocking the current RCU
+ * grace period.
+ */
+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
+{
+ struct rcu_node *rnp = rcu_get_root(rsp);
+
+ rcu_print_detail_task_stall_rnp(rnp);
+ rcu_for_each_leaf_node(rsp, rnp)
+ rcu_print_detail_task_stall_rnp(rnp);
+}
+
+#ifdef CONFIG_RCU_CPU_STALL_INFO
+
+static void rcu_print_task_stall_begin(struct rcu_node *rnp)
+{
+ pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
+ rnp->level, rnp->grplo, rnp->grphi);
+}
+
+static void rcu_print_task_stall_end(void)
+{
+ pr_cont("\n");
+}
+
+#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
+
+static void rcu_print_task_stall_begin(struct rcu_node *rnp)
+{
+}
+
+static void rcu_print_task_stall_end(void)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
+
+/*
+ * Scan the current list of tasks blocked within RCU read-side critical
+ * sections, printing out the tid of each.
+ */
+static int rcu_print_task_stall(struct rcu_node *rnp)
+{
+ struct task_struct *t;
+ int ndetected = 0;
+
+ if (!rcu_preempt_blocked_readers_cgp(rnp))
+ return 0;
+ rcu_print_task_stall_begin(rnp);
+ t = list_entry(rnp->gp_tasks,
+ struct task_struct, rcu_node_entry);
+ list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+ pr_cont(" P%d", t->pid);
+ ndetected++;
+ }
+ rcu_print_task_stall_end();
+ return ndetected;
+}
+
+/*
+ * 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 ->gpnum, and the rnp's ->lock
+ * must be held by the caller.
+ *
+ * Also, if there are blocked tasks on the list, they automatically
+ * block the newly created grace period, so set up ->gp_tasks accordingly.
+ */
+static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
+{
+ WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
+ if (rcu_preempt_has_tasks(rnp))
+ rnp->gp_tasks = rnp->blkd_tasks.next;
+ WARN_ON_ONCE(rnp->qsmask);
+}
+
+/*
+ * Check for a quiescent state from the current CPU. When a task blocks,
+ * the task is recorded in the corresponding CPU's rcu_node structure,
+ * which is checked elsewhere.
+ *
+ * Caller must disable hard irqs.
+ */
+static void rcu_preempt_check_callbacks(void)
+{
+ struct task_struct *t = current;
+
+ if (t->rcu_read_lock_nesting == 0) {
+ rcu_preempt_qs();
+ return;
+ }
+ if (t->rcu_read_lock_nesting > 0 &&
+ __this_cpu_read(rcu_preempt_data.qs_pending) &&
+ !__this_cpu_read(rcu_preempt_data.passed_quiesce))
+ t->rcu_read_unlock_special.b.need_qs = true;
+}
+
+/*
+ * Queue a preemptible-RCU callback for invocation after a grace period.
+ */
+void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
+{
+ __call_rcu(head, func, &rcu_preempt_state, -1, 0);
+}
+EXPORT_SYMBOL_GPL(call_rcu);
+
+/**
+ * synchronize_rcu - wait until a grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full grace
+ * period has elapsed, in other words after all currently executing RCU
+ * read-side critical sections have completed. Note, however, that
+ * upon return from synchronize_rcu(), the caller might well be executing
+ * concurrently with new RCU read-side critical sections that began while
+ * synchronize_rcu() was waiting. RCU read-side critical sections are
+ * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
+ *
+ * See the description of synchronize_sched() for more detailed information
+ * on memory ordering guarantees.
+ */
+void synchronize_rcu(void)
+{
+ rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
+ !lock_is_held(&rcu_lock_map) &&
+ !lock_is_held(&rcu_sched_lock_map),
+ "Illegal synchronize_rcu() in RCU read-side critical section");
+ if (!rcu_scheduler_active)
+ return;
+ if (rcu_gp_is_expedited())
+ synchronize_rcu_expedited();
+ else
+ wait_rcu_gp(call_rcu);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu);
+
+static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
+static unsigned long sync_rcu_preempt_exp_count;
+static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
+
+/*
+ * Return non-zero if there are any tasks in RCU read-side critical
+ * sections blocking the current preemptible-RCU expedited grace period.
+ * If there is no preemptible-RCU expedited grace period currently in
+ * progress, returns zero unconditionally.
+ */
+static int rcu_preempted_readers_exp(struct rcu_node *rnp)
+{
+ return rnp->exp_tasks != NULL;
+}
+
+/*
+ * return non-zero if there is no RCU expedited grace period in progress
+ * for the specified rcu_node structure, in other words, if all CPUs and
+ * tasks covered by the specified rcu_node structure have done their bit
+ * for the current expedited grace period. Works only for preemptible
+ * RCU -- other RCU implementation use other means.
+ *
+ * Caller must hold sync_rcu_preempt_exp_mutex.
+ */
+static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
+{
+ return !rcu_preempted_readers_exp(rnp) &&
+ ACCESS_ONCE(rnp->expmask) == 0;
+}
+
+/*
+ * Report the exit from RCU read-side critical section for the last task
+ * that queued itself during or before the current expedited preemptible-RCU
+ * grace period. This event is reported either to the rcu_node structure on
+ * which the task was queued or to one of that rcu_node structure's ancestors,
+ * recursively up the tree. (Calm down, calm down, we do the recursion
+ * iteratively!)
+ *
+ * Caller must hold sync_rcu_preempt_exp_mutex.
+ */
+static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
+ bool wake)
+{
+ unsigned long flags;
+ unsigned long mask;
+
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ smp_mb__after_unlock_lock();
+ for (;;) {
+ if (!sync_rcu_preempt_exp_done(rnp)) {
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ break;
+ }
+ if (rnp->parent == NULL) {
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ if (wake) {
+ smp_mb(); /* EGP done before wake_up(). */
+ wake_up(&sync_rcu_preempt_exp_wq);
+ }
+ break;
+ }
+ mask = rnp->grpmask;
+ raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
+ rnp = rnp->parent;
+ raw_spin_lock(&rnp->lock); /* irqs already disabled */
+ smp_mb__after_unlock_lock();
+ rnp->expmask &= ~mask;
+ }
+}
+
+/*
+ * Snapshot the tasks blocking the newly started preemptible-RCU expedited
+ * grace period for the specified rcu_node structure, phase 1. If there
+ * are such tasks, set the ->expmask bits up the rcu_node tree and also
+ * set the ->expmask bits on the leaf rcu_node structures to tell phase 2
+ * that work is needed here.
+ *
+ * Caller must hold sync_rcu_preempt_exp_mutex.
+ */
+static void
+sync_rcu_preempt_exp_init1(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+ unsigned long flags;
+ unsigned long mask;
+ struct rcu_node *rnp_up;
+
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ smp_mb__after_unlock_lock();
+ WARN_ON_ONCE(rnp->expmask);
+ WARN_ON_ONCE(rnp->exp_tasks);
+ if (!rcu_preempt_has_tasks(rnp)) {
+ /* No blocked tasks, nothing to do. */
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ return;
+ }
+ /* Call for Phase 2 and propagate ->expmask bits up the tree. */
+ rnp->expmask = 1;
+ rnp_up = rnp;
+ while (rnp_up->parent) {
+ mask = rnp_up->grpmask;
+ rnp_up = rnp_up->parent;
+ if (rnp_up->expmask & mask)
+ break;
+ raw_spin_lock(&rnp_up->lock); /* irqs already off */
+ smp_mb__after_unlock_lock();
+ rnp_up->expmask |= mask;
+ raw_spin_unlock(&rnp_up->lock); /* irqs still off */
+ }
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
+/*
+ * Snapshot the tasks blocking the newly started preemptible-RCU expedited
+ * grace period for the specified rcu_node structure, phase 2. If the
+ * leaf rcu_node structure has its ->expmask field set, check for tasks.
+ * If there are some, clear ->expmask and set ->exp_tasks accordingly,
+ * then initiate RCU priority boosting. Otherwise, clear ->expmask and
+ * invoke rcu_report_exp_rnp() to clear out the upper-level ->expmask bits,
+ * enabling rcu_read_unlock_special() to do the bit-clearing.
+ *
+ * Caller must hold sync_rcu_preempt_exp_mutex.
+ */
+static void
+sync_rcu_preempt_exp_init2(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ smp_mb__after_unlock_lock();
+ if (!rnp->expmask) {
+ /* Phase 1 didn't do anything, so Phase 2 doesn't either. */
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ return;
+ }
+
+ /* Phase 1 is over. */
+ rnp->expmask = 0;
+
+ /*
+ * If there are still blocked tasks, set up ->exp_tasks so that
+ * rcu_read_unlock_special() will wake us and then boost them.
+ */
+ if (rcu_preempt_has_tasks(rnp)) {
+ rnp->exp_tasks = rnp->blkd_tasks.next;
+ rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
+ return;
+ }
+
+ /* No longer any blocked tasks, so undo bit setting. */
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ rcu_report_exp_rnp(rsp, rnp, false);
+}
+
+/**
+ * synchronize_rcu_expedited - Brute-force RCU grace period
+ *
+ * Wait for an RCU-preempt grace period, but expedite it. The basic
+ * idea is to invoke synchronize_sched_expedited() to push all the tasks to
+ * the ->blkd_tasks lists and wait for this list to drain. This consumes
+ * significant time on all CPUs and is unfriendly to real-time workloads,
+ * so is thus not recommended for any sort of common-case code.
+ * In fact, if you are using synchronize_rcu_expedited() in a loop,
+ * please restructure your code to batch your updates, and then Use a
+ * single synchronize_rcu() instead.
+ */
+void synchronize_rcu_expedited(void)
+{
+ struct rcu_node *rnp;
+ struct rcu_state *rsp = &rcu_preempt_state;
+ unsigned long snap;
+ int trycount = 0;
+
+ smp_mb(); /* Caller's modifications seen first by other CPUs. */
+ snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
+ smp_mb(); /* Above access cannot bleed into critical section. */
+
+ /*
+ * Block CPU-hotplug operations. This means that any CPU-hotplug
+ * operation that finds an rcu_node structure with tasks in the
+ * process of being boosted will know that all tasks blocking
+ * this expedited grace period will already be in the process of
+ * being boosted. This simplifies the process of moving tasks
+ * from leaf to root rcu_node structures.
+ */
+ if (!try_get_online_cpus()) {
+ /* CPU-hotplug operation in flight, fall back to normal GP. */
+ wait_rcu_gp(call_rcu);
+ return;
+ }
+
+ /*
+ * Acquire lock, falling back to synchronize_rcu() if too many
+ * lock-acquisition failures. Of course, if someone does the
+ * expedited grace period for us, just leave.
+ */
+ while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
+ if (ULONG_CMP_LT(snap,
+ ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
+ put_online_cpus();
+ goto mb_ret; /* Others did our work for us. */
+ }
+ if (trycount++ < 10) {
+ udelay(trycount * num_online_cpus());
+ } else {
+ put_online_cpus();
+ wait_rcu_gp(call_rcu);
+ return;
+ }
+ }
+ if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
+ put_online_cpus();
+ goto unlock_mb_ret; /* Others did our work for us. */
+ }
+
+ /* force all RCU readers onto ->blkd_tasks lists. */
+ synchronize_sched_expedited();
+
+ /*
+ * Snapshot current state of ->blkd_tasks lists into ->expmask.
+ * Phase 1 sets bits and phase 2 permits rcu_read_unlock_special()
+ * to start clearing them. Doing this in one phase leads to
+ * strange races between setting and clearing bits, so just say "no"!
+ */
+ rcu_for_each_leaf_node(rsp, rnp)
+ sync_rcu_preempt_exp_init1(rsp, rnp);
+ rcu_for_each_leaf_node(rsp, rnp)
+ sync_rcu_preempt_exp_init2(rsp, rnp);
+
+ put_online_cpus();
+
+ /* Wait for snapshotted ->blkd_tasks lists to drain. */
+ rnp = rcu_get_root(rsp);
+ wait_event(sync_rcu_preempt_exp_wq,
+ sync_rcu_preempt_exp_done(rnp));
+
+ /* Clean up and exit. */
+ smp_mb(); /* ensure expedited GP seen before counter increment. */
+ ACCESS_ONCE(sync_rcu_preempt_exp_count) =
+ sync_rcu_preempt_exp_count + 1;
+unlock_mb_ret:
+ mutex_unlock(&sync_rcu_preempt_exp_mutex);
+mb_ret:
+ smp_mb(); /* ensure subsequent action seen after grace period. */
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+/**
+ * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
+ *
+ * Note that this primitive does not necessarily wait for an RCU grace period
+ * to complete. For example, if there are no RCU callbacks queued anywhere
+ * in the system, then rcu_barrier() is within its rights to return
+ * immediately, without waiting for anything, much less an RCU grace period.
+ */
+void rcu_barrier(void)
+{
+ _rcu_barrier(&rcu_preempt_state);
+}
+EXPORT_SYMBOL_GPL(rcu_barrier);
+
+/*
+ * Initialize preemptible RCU's state structures.
+ */
+static void __init __rcu_init_preempt(void)
+{
+ rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
+}
+
+/*
+ * Check for a task exiting while in a preemptible-RCU read-side
+ * critical section, clean up if so. No need to issue warnings,
+ * as debug_check_no_locks_held() already does this if lockdep
+ * is enabled.
+ */
+void exit_rcu(void)
+{
+ struct task_struct *t = current;
+
+ if (likely(list_empty(¤t->rcu_node_entry)))
+ return;
+ t->rcu_read_lock_nesting = 1;
+ barrier();
+ t->rcu_read_unlock_special.b.blocked = true;
+ __rcu_read_unlock();
+}
+
+#else /* #ifdef CONFIG_PREEMPT_RCU */
+
+static struct rcu_state *rcu_state_p = &rcu_sched_state;
+
+/*
+ * Tell them what RCU they are running.
+ */
+static void __init rcu_bootup_announce(void)
+{
+ pr_info("Hierarchical RCU implementation.\n");
+ rcu_bootup_announce_oddness();
+}
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * CPUs being in quiescent states.
+ */
+static void rcu_preempt_note_context_switch(void)
+{
+}
+
+/*
+ * 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 preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections.
+ */
+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
+{
+}
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections.
+ */
+static int rcu_print_task_stall(struct rcu_node *rnp)
+{
+ return 0;
+}
+
+/*
+ * Because 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);
+}
+
+/*
+ * Because preemptible RCU does not exist, it never has any callbacks
+ * to check.
+ */
+static void rcu_preempt_check_callbacks(void)
+{
+}
+
+/*
+ * Wait for an rcu-preempt grace period, but make it happen quickly.
+ * But because preemptible RCU does not exist, map to rcu-sched.
+ */
+void synchronize_rcu_expedited(void)
+{
+ synchronize_sched_expedited();
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+/*
+ * Because preemptible RCU does not exist, rcu_barrier() is just
+ * another name for rcu_barrier_sched().
+ */
+void rcu_barrier(void)
+{
+ rcu_barrier_sched();
+}
+EXPORT_SYMBOL_GPL(rcu_barrier);
+
+/*
+ * Because preemptible RCU does not exist, it need not be initialized.
+ */
+static void __init __rcu_init_preempt(void)
+{
+}
+
+/*
+ * Because preemptible RCU does not exist, tasks cannot possibly exit
+ * while in preemptible RCU read-side critical sections.
+ */
+void exit_rcu(void)
+{
+}
+
+#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
+
+#include "../locking/rtmutex_common.h"
+
+#ifdef CONFIG_RCU_TRACE
+
+static void rcu_initiate_boost_trace(struct rcu_node *rnp)
+{
+ if (!rcu_preempt_has_tasks(rnp))
+ rnp->n_balk_blkd_tasks++;
+ else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
+ rnp->n_balk_exp_gp_tasks++;
+ else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
+ rnp->n_balk_boost_tasks++;
+ else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
+ rnp->n_balk_notblocked++;
+ else if (rnp->gp_tasks != NULL &&
+ ULONG_CMP_LT(jiffies, rnp->boost_time))
+ rnp->n_balk_notyet++;
+ else
+ rnp->n_balk_nos++;
+}
+
+#else /* #ifdef CONFIG_RCU_TRACE */
+
+static void rcu_initiate_boost_trace(struct rcu_node *rnp)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_TRACE */
+
+/*
+ * 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 (ACCESS_ONCE(rnp->exp_tasks) == NULL &&
+ ACCESS_ONCE(rnp->boost_tasks) == NULL)
+ return 0; /* Nothing left to boost. */
+
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ smp_mb__after_unlock_lock();
+
+ /*
+ * 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(&rnp->lock, 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;
+ rnp->n_exp_boosts++;
+ } else {
+ tb = rnp->boost_tasks;
+ rnp->n_normal_boosts++;
+ }
+ rnp->n_tasks_boosted++;
+
+ /*
+ * 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(&rnp->lock, 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 ACCESS_ONCE(rnp->exp_tasks) != NULL ||
+ ACCESS_ONCE(rnp->boost_tasks) != NULL;
+}
+
+/*
+ * Priority-boosting kthread. One per leaf rcu_node and one for the
+ * root rcu_node.
+ */
+static int rcu_boost_kthread(void *arg)
+{
+ struct rcu_node *rnp = (struct rcu_node *)arg;
+ int spincnt = 0;
+ int more2boost;
+
+ trace_rcu_utilization(TPS("Start boost kthread@init"));
+ for (;;) {
+ rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
+ trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
+ rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
+ trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
+ rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
+ more2boost = rcu_boost(rnp);
+ if (more2boost)
+ spincnt++;
+ else
+ spincnt = 0;
+ if (spincnt > 10) {
+ rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
+ trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
+ schedule_timeout_interruptible(2);
+ trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
+ spincnt = 0;
+ }
+ }
+ /* NOTREACHED */
+ trace_rcu_utilization(TPS("End boost kthread@notreached"));
+ return 0;
+}
+
+/*
+ * Check to see if it is time to start boosting RCU readers that are
+ * blocking the current grace period, and, if so, tell the per-rcu_node
+ * kthread to start boosting them. If there is an expedited grace
+ * period in progress, it is always time to boost.
+ *
+ * The caller must hold rnp->lock, which this function releases.
+ * The ->boost_kthread_task is immortal, so we don't need to worry
+ * about it going away.
+ */
+static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
+ __releases(rnp->lock)
+{
+ struct task_struct *t;
+
+ if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
+ rnp->n_balk_exp_gp_tasks++;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ return;
+ }
+ if (rnp->exp_tasks != NULL ||
+ (rnp->gp_tasks != NULL &&
+ rnp->boost_tasks == NULL &&
+ rnp->qsmask == 0 &&
+ ULONG_CMP_GE(jiffies, rnp->boost_time))) {
+ if (rnp->exp_tasks == NULL)
+ rnp->boost_tasks = rnp->gp_tasks;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ t = rnp->boost_kthread_task;
+ if (t)
+ rcu_wake_cond(t, rnp->boost_kthread_status);
+ } else {
+ rcu_initiate_boost_trace(rnp);
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ }
+}
+
+/*
+ * Is the current CPU running the RCU-callbacks kthread?
+ * Caller must have preemption disabled.
+ */
+static bool rcu_is_callbacks_kthread(void)
+{
+ return __this_cpu_read(rcu_cpu_kthread_task) == current;
+}
+
+#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
+
+/*
+ * Do priority-boost accounting for the start of a new grace period.
+ */
+static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
+{
+ rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
+}
+
+/*
+ * Create an RCU-boost kthread for the specified node if one does not
+ * already exist. We only create this kthread for preemptible RCU.
+ * Returns zero if all is well, a negated errno otherwise.
+ */
+static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
+ struct rcu_node *rnp)
+{
+ int rnp_index = rnp - &rsp->node[0];
+ unsigned long flags;
+ struct sched_param sp;
+ struct task_struct *t;
+
+ if (&rcu_preempt_state != rsp)
+ return 0;
+
+ if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
+ return 0;
+
+ rsp->boost = 1;
+ if (rnp->boost_kthread_task != NULL)
+ return 0;
+ t = kthread_create(rcu_boost_kthread, (void *)rnp,
+ "rcub/%d", rnp_index);
+ if (IS_ERR(t))
+ return PTR_ERR(t);
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ smp_mb__after_unlock_lock();
+ rnp->boost_kthread_task = t;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ sp.sched_priority = kthread_prio;
+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+ wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
+ return 0;
+}
+
+/*
+ * 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 (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
+ if ((mask & 0x1) && 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(rcu_state_p, rnp)
+ (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
+}
+
+static void rcu_prepare_kthreads(int cpu)
+{
+ struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
+ struct rcu_node *rnp = rdp->mynode;
+
+ /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
+ if (rcu_scheduler_fully_active)
+ (void)rcu_spawn_one_boost_kthread(rcu_state_p, 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(&rnp->lock, 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) || defined(CONFIG_PREEMPT_RT_FULL)
+
+/*
+ * Check to see if any future RCU-related work will need to be done
+ * by the current CPU, even if none need be done immediately, returning
+ * 1 if so. This function is part of the RCU implementation; it is -not-
+ * an exported member of the RCU API.
+ *
+ * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
+ * any flavor of RCU.
+ */
+#ifndef CONFIG_RCU_NOCB_CPU_ALL
+int rcu_needs_cpu(unsigned long *delta_jiffies)
+{
+ *delta_jiffies = ULONG_MAX;
+ return rcu_cpu_has_callbacks(NULL);
+}
+#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
+#endif /* !defined(CONFIG_RCU_FAST_NO_HZ) || defined(CONFIG_PREEMPT_RT_FULL) */
+
+#if !defined(CONFIG_RCU_FAST_NO_HZ)
+/*
+ * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
+ * after it.
+ */
+static void rcu_cleanup_after_idle(void)
+{
+}
+
+/*
+ * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
+ * is nothing.
+ */
+static void rcu_prepare_for_idle(void)
+{
+}
+
+/*
+ * Don't bother keeping a running count of the number of RCU callbacks
+ * posted because CONFIG_RCU_FAST_NO_HZ=n.
+ */
+static void rcu_idle_count_callbacks_posted(void)
+{
+}
+
+#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
+
+/*
+ * This code is invoked when a CPU goes idle, at which point we want
+ * to have the CPU do everything required for RCU so that it can enter
+ * the energy-efficient dyntick-idle mode. This is handled by a
+ * state machine implemented by rcu_prepare_for_idle() below.
+ *
+ * The following three proprocessor symbols control this state machine:
+ *
+ * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
+ * to sleep in dyntick-idle mode with RCU callbacks pending. This
+ * is sized to be roughly one RCU grace period. Those energy-efficiency
+ * benchmarkers who might otherwise be tempted to set this to a large
+ * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
+ * system. And if you are -that- concerned about energy efficiency,
+ * just power the system down and be done with it!
+ * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
+ * permitted to sleep in dyntick-idle mode with only lazy RCU
+ * callbacks pending. Setting this too high can OOM your system.
+ *
+ * The values below work well in practice. If future workloads require
+ * adjustment, they can be converted into kernel config parameters, though
+ * making the state machine smarter might be a better option.
+ */
+#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
+#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
+
+static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
+module_param(rcu_idle_gp_delay, int, 0644);
+static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
+module_param(rcu_idle_lazy_gp_delay, int, 0644);
+
+extern int tick_nohz_active;
+
+/*
+ * Try to advance callbacks for all flavors of RCU 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;
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+ struct rcu_node *rnp;
+ struct rcu_state *rsp;
+
+ /* Exit early if we advanced recently. */
+ if (jiffies == rdtp->last_advance_all)
+ return false;
+ rdtp->last_advance_all = jiffies;
+
+ for_each_rcu_flavor(rsp) {
+ rdp = this_cpu_ptr(rsp->rda);
+ 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 ((rdp->completed != rnp->completed ||
+ unlikely(ACCESS_ONCE(rdp->gpwrap))) &&
+ rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
+ note_gp_changes(rsp, rdp);
+
+ if (cpu_has_callbacks_ready_to_invoke(rdp))
+ cbs_ready = true;
+ }
+ return cbs_ready;
+}
+
+#ifndef CONFIG_PREEMPT_RT_FULL
+
+/*
+ * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
+ * to invoke. If the CPU has callbacks, try to advance them. Tell the
+ * caller to set the timeout based on whether or not there are non-lazy
+ * callbacks.
+ *
+ * The caller must have disabled interrupts.
+ */
+#ifndef CONFIG_RCU_NOCB_CPU_ALL
+int rcu_needs_cpu(unsigned long *dj)
+{
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+
+ /* Snapshot to detect later posting of non-lazy callback. */
+ rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
+
+ /* If no callbacks, RCU doesn't need the CPU. */
+ if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) {
+ *dj = ULONG_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;
+ }
+ rdtp->last_accelerate = jiffies;
+
+ /* Request timer delay depending on laziness, and round. */
+ if (!rdtp->all_lazy) {
+ *dj = round_up(rcu_idle_gp_delay + jiffies,
+ rcu_idle_gp_delay) - jiffies;
+ } else {
+ *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
+ }
+ return 0;
+}
+#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
+#endif /* #ifndef CONFIG_PREEMPT_RT_FULL */
+/*
+ * Prepare a CPU for idle from an RCU perspective. The first major task
+ * is to sense whether nohz mode has been enabled or disabled via sysfs.
+ * The second major task is to check to see if a non-lazy callback has
+ * arrived at a CPU that previously had only lazy callbacks. The third
+ * major task is to accelerate (that is, assign grace-period numbers to)
+ * any recently arrived callbacks.
+ *
+ * The caller must have disabled interrupts.
+ */
+static void rcu_prepare_for_idle(void)
+{
+#ifndef CONFIG_RCU_NOCB_CPU_ALL
+ bool needwake;
+ struct rcu_data *rdp;
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+ struct rcu_node *rnp;
+ struct rcu_state *rsp;
+ int tne;
+
+ /* Handle nohz enablement switches conservatively. */
+ tne = ACCESS_ONCE(tick_nohz_active);
+ if (tne != rdtp->tick_nohz_enabled_snap) {
+ if (rcu_cpu_has_callbacks(NULL))
+ invoke_rcu_core(); /* force nohz to see update. */
+ rdtp->tick_nohz_enabled_snap = tne;
+ return;
+ }
+ if (!tne)
+ return;
+
+ /* If this is a no-CBs CPU, no callbacks, just return. */
+ if (rcu_is_nocb_cpu(smp_processor_id()))
+ return;
+
+ /*
+ * If a non-lazy callback arrived at a CPU having only lazy
+ * callbacks, invoke RCU core for the side-effect of recalculating
+ * idle duration on re-entry to idle.
+ */
+ if (rdtp->all_lazy &&
+ rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
+ rdtp->all_lazy = false;
+ rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
+ invoke_rcu_core();
+ return;
+ }
+
+ /*
+ * If we have not yet accelerated this jiffy, accelerate all
+ * callbacks on this CPU.
+ */
+ if (rdtp->last_accelerate == jiffies)
+ return;
+ rdtp->last_accelerate = jiffies;
+ for_each_rcu_flavor(rsp) {
+ rdp = this_cpu_ptr(rsp->rda);
+ if (!*rdp->nxttail[RCU_DONE_TAIL])
+ continue;
+ rnp = rdp->mynode;
+ raw_spin_lock(&rnp->lock); /* irqs already disabled. */
+ smp_mb__after_unlock_lock();
+ needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
+ raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
+ if (needwake)
+ rcu_gp_kthread_wake(rsp);
+ }
+#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
+}
+
+/*
+ * 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)
+{
+#ifndef CONFIG_RCU_NOCB_CPU_ALL
+ if (rcu_is_nocb_cpu(smp_processor_id()))
+ return;
+ if (rcu_try_advance_all_cbs())
+ invoke_rcu_core();
+#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
+}
+
+/*
+ * Keep a running count of the number of non-lazy callbacks posted
+ * on this CPU. This running counter (which is never decremented) allows
+ * rcu_prepare_for_idle() to detect when something out of the idle loop
+ * posts a callback, even if an equal number of callbacks are invoked.
+ * Of course, callbacks should only be posted from within a trace event
+ * designed to be called from idle or from within RCU_NONIDLE().
+ */
+static void rcu_idle_count_callbacks_posted(void)
+{
+ __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
+}
+
+/*
+ * Data for flushing lazy RCU callbacks at OOM time.
+ */
+static atomic_t oom_callback_count;
+static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
+
+/*
+ * RCU OOM callback -- decrement the outstanding count and deliver the
+ * wake-up if we are the last one.
+ */
+static void rcu_oom_callback(struct rcu_head *rhp)
+{
+ if (atomic_dec_and_test(&oom_callback_count))
+ wake_up(&oom_callback_wq);
+}
+
+/*
+ * Post an rcu_oom_notify callback on the current CPU if it has at
+ * least one lazy callback. This will unnecessarily post callbacks
+ * to CPUs that already have a non-lazy callback at the end of their
+ * callback list, but this is an infrequent operation, so accept some
+ * extra overhead to keep things simple.
+ */
+static void rcu_oom_notify_cpu(void *unused)
+{
+ struct rcu_state *rsp;
+ struct rcu_data *rdp;
+
+ for_each_rcu_flavor(rsp) {
+ rdp = raw_cpu_ptr(rsp->rda);
+ if (rdp->qlen_lazy != 0) {
+ atomic_inc(&oom_callback_count);
+ rsp->call(&rdp->oom_head, rcu_oom_callback);
+ }
+ }
+}
+
+/*
+ * If low on memory, ensure that each CPU has a non-lazy callback.
+ * This will wake up CPUs that have only lazy callbacks, in turn
+ * ensuring that they free up the corresponding memory in a timely manner.
+ * Because an uncertain amount of memory will be freed in some uncertain
+ * timeframe, we do not claim to have freed anything.
+ */
+static int rcu_oom_notify(struct notifier_block *self,
+ unsigned long notused, void *nfreed)
+{
+ int cpu;
+
+ /* Wait for callbacks from earlier instance to complete. */
+ wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
+ smp_mb(); /* Ensure callback reuse happens after callback invocation. */
+
+ /*
+ * Prevent premature wakeup: ensure that all increments happen
+ * before there is a chance of the counter reaching zero.
+ */
+ atomic_set(&oom_callback_count, 1);
+
+ get_online_cpus();
+ for_each_online_cpu(cpu) {
+ smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
+ cond_resched_rcu_qs();
+ }
+ put_online_cpus();
+
+ /* Unconditionally decrement: no need to wake ourselves up. */
+ atomic_dec(&oom_callback_count);
+
+ return NOTIFY_OK;
+}
+
+static struct notifier_block rcu_oom_nb = {
+ .notifier_call = rcu_oom_notify
+};
+
+static int __init rcu_register_oom_notifier(void)
+{
+ register_oom_notifier(&rcu_oom_nb);
+ return 0;
+}
+early_initcall(rcu_register_oom_notifier);
+
+#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
+
+#ifdef CONFIG_RCU_CPU_STALL_INFO
+
+#ifdef CONFIG_RCU_FAST_NO_HZ
+
+static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
+{
+ struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
+ unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
+
+ sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
+ rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
+ ulong2long(nlpd),
+ rdtp->all_lazy ? 'L' : '.',
+ rdtp->tick_nohz_enabled_snap ? '.' : 'D');
+}
+
+#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
+
+static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
+{
+ *cp = '\0';
+}
+
+#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
+
+/* Initiate the stall-info list. */
+static void print_cpu_stall_info_begin(void)
+{
+ pr_cont("\n");
+}
+
+/*
+ * Print out diagnostic information for the specified stalled CPU.
+ *
+ * If the specified CPU is aware of the current RCU grace period
+ * (flavor specified by rsp), then print the number of scheduling
+ * clock interrupts the CPU has taken during the time that it has
+ * been aware. Otherwise, print the number of RCU grace periods
+ * that this CPU is ignorant of, for example, "1" if the CPU was
+ * aware of the previous grace period.
+ *
+ * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
+ */
+static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
+{
+ char fast_no_hz[72];
+ struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+ struct rcu_dynticks *rdtp = rdp->dynticks;
+ char *ticks_title;
+ unsigned long ticks_value;
+
+ if (rsp->gpnum == rdp->gpnum) {
+ ticks_title = "ticks this GP";
+ ticks_value = rdp->ticks_this_gp;
+ } else {
+ ticks_title = "GPs behind";
+ ticks_value = rsp->gpnum - rdp->gpnum;
+ }
+ print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
+ pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n",
+ cpu, ticks_value, ticks_title,
+ atomic_read(&rdtp->dynticks) & 0xfff,
+ rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
+ rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
+ ACCESS_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
+ fast_no_hz);
+}
+
+/* Terminate the stall-info list. */
+static void print_cpu_stall_info_end(void)
+{
+ pr_err("\t");
+}
+
+/* Zero ->ticks_this_gp for all flavors of RCU. */
+static void zero_cpu_stall_ticks(struct rcu_data *rdp)
+{
+ rdp->ticks_this_gp = 0;
+ rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
+}
+
+/* Increment ->ticks_this_gp for all flavors of RCU. */
+static void increment_cpu_stall_ticks(void)
+{
+ struct rcu_state *rsp;
+
+ for_each_rcu_flavor(rsp)
+ raw_cpu_inc(rsp->rda->ticks_this_gp);
+}
+
+#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
+
+static void print_cpu_stall_info_begin(void)
+{
+ pr_cont(" {");
+}
+
+static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
+{
+ pr_cont(" %d", cpu);
+}
+
+static void print_cpu_stall_info_end(void)
+{
+ pr_cont("} ");
+}
+
+static void zero_cpu_stall_ticks(struct rcu_data *rdp)
+{
+}
+
+static void increment_cpu_stall_ticks(void)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
+
+#ifdef CONFIG_RCU_NOCB_CPU
+
+/*
+ * Offload callback processing from the boot-time-specified set of CPUs
+ * specified by rcu_nocb_mask. For each CPU in the set, there is a
+ * kthread created that pulls the callbacks from the corresponding CPU,
+ * waits for a grace period to elapse, and invokes the callbacks.
+ * The no-CBs CPUs do a wake_up() on their kthread when they insert
+ * a callback into any empty list, unless the rcu_nocb_poll boot parameter
+ * has been specified, in which case each kthread actively polls its
+ * CPU. (Which isn't so great for energy efficiency, but which does
+ * reduce RCU's overhead on that CPU.)
+ *
+ * This is intended to be used in conjunction with Frederic Weisbecker's
+ * adaptive-idle work, which would seriously reduce OS jitter on CPUs
+ * running CPU-bound user-mode computations.
+ *
+ * Offloading of callback processing could also in theory be used as
+ * an energy-efficiency measure because CPUs with no RCU callbacks
+ * queued are more aggressive about entering dyntick-idle mode.
+ */
+
+
+/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
+static int __init rcu_nocb_setup(char *str)
+{
+ alloc_bootmem_cpumask_var(&rcu_nocb_mask);
+ have_rcu_nocb_mask = true;
+ cpulist_parse(str, rcu_nocb_mask);
+ return 1;
+}
+__setup("rcu_nocbs=", rcu_nocb_setup);
+
+static int __init parse_rcu_nocb_poll(char *arg)
+{
+ rcu_nocb_poll = 1;
+ return 0;
+}
+early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
+
+/*
+ * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
+ * grace period.
+ */
+static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+ swait_wake_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
+}
+
+/*
+ * Set the root rcu_node structure's ->need_future_gp field
+ * based on the sum of those of all rcu_node structures. This does
+ * double-count the root rcu_node structure's requests, but this
+ * is necessary to handle the possibility of a rcu_nocb_kthread()
+ * having awakened during the time that the rcu_node structures
+ * were being updated for the end of the previous grace period.
+ */
+static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
+{
+ rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
+}
+
+static void rcu_init_one_nocb(struct rcu_node *rnp)
+{
+ init_swait_head(&rnp->nocb_gp_wq[0]);
+ init_swait_head(&rnp->nocb_gp_wq[1]);
+}
+
+#ifndef CONFIG_RCU_NOCB_CPU_ALL
+/* Is the specified CPU a no-CBs CPU? */
+bool rcu_is_nocb_cpu(int cpu)
+{
+ if (have_rcu_nocb_mask)
+ return cpumask_test_cpu(cpu, rcu_nocb_mask);
+ return false;
+}
+#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
+
+/*
+ * Kick the leader kthread for this NOCB group.
+ */
+static void wake_nocb_leader(struct rcu_data *rdp, bool force)
+{
+ struct rcu_data *rdp_leader = rdp->nocb_leader;
+
+ if (!ACCESS_ONCE(rdp_leader->nocb_kthread))
+ return;
+ if (ACCESS_ONCE(rdp_leader->nocb_leader_sleep) || force) {
+ /* Prior smp_mb__after_atomic() orders against prior enqueue. */
+ ACCESS_ONCE(rdp_leader->nocb_leader_sleep) = false;
+ swait_wake(&rdp_leader->nocb_wq);
+ }
+}
+
+/*
+ * Does the specified CPU need an RCU callback for the specified flavor
+ * of rcu_barrier()?
+ */
+static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
+{
+ struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
+ unsigned long ret;
+#ifdef CONFIG_PROVE_RCU
+ struct rcu_head *rhp;
+#endif /* #ifdef CONFIG_PROVE_RCU */
+
+ /*
+ * Check count of all no-CBs callbacks awaiting invocation.
+ * There needs to be a barrier before this function is called,
+ * but associated with a prior determination that no more
+ * callbacks would be posted. In the worst case, the first
+ * barrier in _rcu_barrier() suffices (but the caller cannot
+ * necessarily rely on this, not a substitute for the caller
+ * getting the concurrency design right!). There must also be
+ * a barrier between the following load an posting of a callback
+ * (if a callback is in fact needed). This is associated with an
+ * atomic_inc() in the caller.
+ */
+ ret = atomic_long_read(&rdp->nocb_q_count);
+
+#ifdef CONFIG_PROVE_RCU
+ rhp = ACCESS_ONCE(rdp->nocb_head);
+ if (!rhp)
+ rhp = ACCESS_ONCE(rdp->nocb_gp_head);
+ if (!rhp)
+ rhp = ACCESS_ONCE(rdp->nocb_follower_head);
+
+ /* Having no rcuo kthread but CBs after scheduler starts is bad! */
+ if (!ACCESS_ONCE(rdp->nocb_kthread) && rhp &&
+ rcu_scheduler_fully_active) {
+ /* RCU callback enqueued before CPU first came online??? */
+ pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
+ cpu, rhp->func);
+ WARN_ON_ONCE(1);
+ }
+#endif /* #ifdef CONFIG_PROVE_RCU */
+
+ return !!ret;
+}
+
+/*
+ * Enqueue the specified string of rcu_head structures onto the specified
+ * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
+ * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
+ * counts are supplied by rhcount and rhcount_lazy.
+ *
+ * If warranted, also wake up the kthread servicing this CPUs queues.
+ */
+static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
+ struct rcu_head *rhp,
+ struct rcu_head **rhtp,
+ int rhcount, int rhcount_lazy,
+ unsigned long flags)
+{
+ int len;
+ struct rcu_head **old_rhpp;
+ struct task_struct *t;
+
+ /* Enqueue the callback on the nocb list and update counts. */
+ atomic_long_add(rhcount, &rdp->nocb_q_count);
+ /* rcu_barrier() relies on ->nocb_q_count add before xchg. */
+ old_rhpp = xchg(&rdp->nocb_tail, rhtp);
+ ACCESS_ONCE(*old_rhpp) = rhp;
+ atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
+ smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
+
+ /* If we are not being polled and there is a kthread, awaken it ... */
+ t = ACCESS_ONCE(rdp->nocb_kthread);
+ if (rcu_nocb_poll || !t) {
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ TPS("WakeNotPoll"));
+ return;
+ }
+ len = atomic_long_read(&rdp->nocb_q_count);
+ if (old_rhpp == &rdp->nocb_head) {
+ if (!irqs_disabled_flags(flags)) {
+ /* ... if queue was empty ... */
+ wake_nocb_leader(rdp, false);
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ TPS("WakeEmpty"));
+ } else {
+ rdp->nocb_defer_wakeup = RCU_NOGP_WAKE;
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ TPS("WakeEmptyIsDeferred"));
+ }
+ rdp->qlen_last_fqs_check = 0;
+ } else if (len > rdp->qlen_last_fqs_check + qhimark) {
+ /* ... or if many callbacks queued. */
+ if (!irqs_disabled_flags(flags)) {
+ wake_nocb_leader(rdp, true);
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ TPS("WakeOvf"));
+ } else {
+ rdp->nocb_defer_wakeup = RCU_NOGP_WAKE_FORCE;
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ TPS("WakeOvfIsDeferred"));
+ }
+ rdp->qlen_last_fqs_check = LONG_MAX / 2;
+ } else {
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
+ }
+ return;
+}
+
+/*
+ * This is a helper for __call_rcu(), which invokes this when the normal
+ * callback queue is inoperable. If this is not a no-CBs CPU, this
+ * function returns failure back to __call_rcu(), which can complain
+ * appropriately.
+ *
+ * Otherwise, this function queues the callback where the corresponding
+ * "rcuo" kthread can find it.
+ */
+static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
+ bool lazy, unsigned long flags)
+{
+
+ if (!rcu_is_nocb_cpu(rdp->cpu))
+ return false;
+ __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
+ if (__is_kfree_rcu_offset((unsigned long)rhp->func))
+ trace_rcu_kfree_callback(rdp->rsp->name, rhp,
+ (unsigned long)rhp->func,
+ -atomic_long_read(&rdp->nocb_q_count_lazy),
+ -atomic_long_read(&rdp->nocb_q_count));
+ else
+ trace_rcu_callback(rdp->rsp->name, rhp,
+ -atomic_long_read(&rdp->nocb_q_count_lazy),
+ -atomic_long_read(&rdp->nocb_q_count));
+
+ /*
+ * If called from an extended quiescent state with interrupts
+ * disabled, invoke the RCU core in order to allow the idle-entry
+ * deferred-wakeup check to function.
+ */
+ if (irqs_disabled_flags(flags) &&
+ !rcu_is_watching() &&
+ cpu_online(smp_processor_id()))
+ invoke_rcu_core();
+
+ return true;
+}
+
+/*
+ * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
+ * not a no-CBs CPU.
+ */
+static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
+ struct rcu_data *rdp,
+ unsigned long flags)
+{
+ long ql = rsp->qlen;
+ long qll = rsp->qlen_lazy;
+
+ /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
+ if (!rcu_is_nocb_cpu(smp_processor_id()))
+ return false;
+ rsp->qlen = 0;
+ rsp->qlen_lazy = 0;
+
+ /* First, enqueue the donelist, if any. This preserves CB ordering. */
+ if (rsp->orphan_donelist != NULL) {
+ __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
+ rsp->orphan_donetail, ql, qll, flags);
+ ql = qll = 0;
+ rsp->orphan_donelist = NULL;
+ rsp->orphan_donetail = &rsp->orphan_donelist;
+ }
+ if (rsp->orphan_nxtlist != NULL) {
+ __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
+ rsp->orphan_nxttail, ql, qll, flags);
+ ql = qll = 0;
+ rsp->orphan_nxtlist = NULL;
+ rsp->orphan_nxttail = &rsp->orphan_nxtlist;
+ }
+ return true;
+}
+
+/*
+ * If necessary, kick off a new grace period, and either way wait
+ * for a subsequent grace period to complete.
+ */
+static void rcu_nocb_wait_gp(struct rcu_data *rdp)
+{
+ unsigned long c;
+ bool d;
+ unsigned long flags;
+ bool needwake;
+ struct rcu_node *rnp = rdp->mynode;
+
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ smp_mb__after_unlock_lock();
+ needwake = rcu_start_future_gp(rnp, rdp, &c);
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ if (needwake)
+ rcu_gp_kthread_wake(rdp->rsp);
+
+ /*
+ * Wait for the grace period. Do so interruptibly to avoid messing
+ * up the load average.
+ */
+ trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
+ for (;;) {
+ swait_event_interruptible(
+ rnp->nocb_gp_wq[c & 0x1],
+ (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
+ if (likely(d))
+ break;
+ WARN_ON(signal_pending(current));
+ trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
+ }
+ trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
+ smp_mb(); /* Ensure that CB invocation happens after GP end. */
+}
+
+/*
+ * Leaders come here to wait for additional callbacks to show up.
+ * This function does not return until callbacks appear.
+ */
+static void nocb_leader_wait(struct rcu_data *my_rdp)
+{
+ bool firsttime = true;
+ bool gotcbs;
+ struct rcu_data *rdp;
+ struct rcu_head **tail;
+
+wait_again:
+
+ /* Wait for callbacks to appear. */
+ if (!rcu_nocb_poll) {
+ trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep");
+ swait_event_interruptible(my_rdp->nocb_wq,
+ !ACCESS_ONCE(my_rdp->nocb_leader_sleep));
+ /* Memory barrier handled by smp_mb() calls below and repoll. */
+ } else if (firsttime) {
+ firsttime = false; /* Don't drown trace log with "Poll"! */
+ trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Poll");
+ }
+
+ /*
+ * Each pass through the following loop checks a follower for CBs.
+ * We are our own first follower. Any CBs found are moved to
+ * nocb_gp_head, where they await a grace period.
+ */
+ gotcbs = false;
+ for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
+ rdp->nocb_gp_head = ACCESS_ONCE(rdp->nocb_head);
+ if (!rdp->nocb_gp_head)
+ continue; /* No CBs here, try next follower. */
+
+ /* Move callbacks to wait-for-GP list, which is empty. */
+ ACCESS_ONCE(rdp->nocb_head) = NULL;
+ rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
+ gotcbs = true;
+ }
+
+ /*
+ * If there were no callbacks, sleep a bit, rescan after a
+ * memory barrier, and go retry.
+ */
+ if (unlikely(!gotcbs)) {
+ if (!rcu_nocb_poll)
+ trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
+ "WokeEmpty");
+ WARN_ON(signal_pending(current));
+ schedule_timeout_interruptible(1);
+
+ /* Rescan in case we were a victim of memory ordering. */
+ my_rdp->nocb_leader_sleep = true;
+ smp_mb(); /* Ensure _sleep true before scan. */
+ for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower)
+ if (ACCESS_ONCE(rdp->nocb_head)) {
+ /* Found CB, so short-circuit next wait. */
+ my_rdp->nocb_leader_sleep = false;
+ break;
+ }
+ goto wait_again;
+ }
+
+ /* Wait for one grace period. */
+ rcu_nocb_wait_gp(my_rdp);
+
+ /*
+ * We left ->nocb_leader_sleep unset to reduce cache thrashing.
+ * We set it now, but recheck for new callbacks while
+ * traversing our follower list.
+ */
+ my_rdp->nocb_leader_sleep = true;
+ smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */
+
+ /* Each pass through the following loop wakes a follower, if needed. */
+ for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
+ if (ACCESS_ONCE(rdp->nocb_head))
+ my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
+ if (!rdp->nocb_gp_head)
+ continue; /* No CBs, so no need to wake follower. */
+
+ /* Append callbacks to follower's "done" list. */
+ tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail);
+ *tail = rdp->nocb_gp_head;
+ smp_mb__after_atomic(); /* Store *tail before wakeup. */
+ if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
+ /*
+ * List was empty, wake up the follower.
+ * Memory barriers supplied by atomic_long_add().
+ */
+ swait_wake(&rdp->nocb_wq);
+ }
+ }
+
+ /* If we (the leader) don't have CBs, go wait some more. */
+ if (!my_rdp->nocb_follower_head)
+ goto wait_again;
+}
+
+/*
+ * Followers come here to wait for additional callbacks to show up.
+ * This function does not return until callbacks appear.
+ */
+static void nocb_follower_wait(struct rcu_data *rdp)
+{
+ bool firsttime = true;
+
+ for (;;) {
+ if (!rcu_nocb_poll) {
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ "FollowerSleep");
+ swait_event_interruptible(rdp->nocb_wq,
+ ACCESS_ONCE(rdp->nocb_follower_head));
+ } else if (firsttime) {
+ /* Don't drown trace log with "Poll"! */
+ firsttime = false;
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "Poll");
+ }
+ if (smp_load_acquire(&rdp->nocb_follower_head)) {
+ /* ^^^ Ensure CB invocation follows _head test. */
+ return;
+ }
+ if (!rcu_nocb_poll)
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ "WokeEmpty");
+ WARN_ON(signal_pending(current));
+ schedule_timeout_interruptible(1);
+ }
+}
+
+/*
+ * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
+ * callbacks queued by the corresponding no-CBs CPU, however, there is
+ * an optional leader-follower relationship so that the grace-period
+ * kthreads don't have to do quite so many wakeups.
+ */
+static int rcu_nocb_kthread(void *arg)
+{
+ int c, cl;
+ struct rcu_head *list;
+ struct rcu_head *next;
+ struct rcu_head **tail;
+ struct rcu_data *rdp = arg;
+
+ /* Each pass through this loop invokes one batch of callbacks */
+ for (;;) {
+ /* Wait for callbacks. */
+ if (rdp->nocb_leader == rdp)
+ nocb_leader_wait(rdp);
+ else
+ nocb_follower_wait(rdp);
+
+ /* Pull the ready-to-invoke callbacks onto local list. */
+ list = ACCESS_ONCE(rdp->nocb_follower_head);
+ BUG_ON(!list);
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty");
+ ACCESS_ONCE(rdp->nocb_follower_head) = NULL;
+ tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head);
+
+ /* Each pass through the following loop invokes a callback. */
+ trace_rcu_batch_start(rdp->rsp->name,
+ atomic_long_read(&rdp->nocb_q_count_lazy),
+ atomic_long_read(&rdp->nocb_q_count), -1);
+ c = cl = 0;
+ while (list) {
+ next = list->next;
+ /* Wait for enqueuing to complete, if needed. */
+ while (next == NULL && &list->next != tail) {
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ TPS("WaitQueue"));
+ schedule_timeout_interruptible(1);
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+ TPS("WokeQueue"));
+ next = list->next;
+ }
+ debug_rcu_head_unqueue(list);
+ local_bh_disable();
+ if (__rcu_reclaim(rdp->rsp->name, list))
+ cl++;
+ c++;
+ local_bh_enable();
+ list = next;
+ }
+ trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
+ smp_mb__before_atomic(); /* _add after CB invocation. */
+ atomic_long_add(-c, &rdp->nocb_q_count);
+ atomic_long_add(-cl, &rdp->nocb_q_count_lazy);
+ rdp->n_nocbs_invoked += c;
+ }
+ return 0;
+}
+
+/* Is a deferred wakeup of rcu_nocb_kthread() required? */
+static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
+{
+ return ACCESS_ONCE(rdp->nocb_defer_wakeup);
+}
+
+/* Do a deferred wakeup of rcu_nocb_kthread(). */
+static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
+{
+ int ndw;
+
+ if (!rcu_nocb_need_deferred_wakeup(rdp))
+ return;
+ ndw = ACCESS_ONCE(rdp->nocb_defer_wakeup);
+ ACCESS_ONCE(rdp->nocb_defer_wakeup) = RCU_NOGP_WAKE_NOT;
+ wake_nocb_leader(rdp, ndw == RCU_NOGP_WAKE_FORCE);
+ trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake"));
+}
+
+void __init rcu_init_nohz(void)
+{
+ int cpu;
+ bool need_rcu_nocb_mask = true;
+ struct rcu_state *rsp;
+
+#ifdef CONFIG_RCU_NOCB_CPU_NONE
+ need_rcu_nocb_mask = false;
+#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
+
+#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 (!have_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;
+ }
+ have_rcu_nocb_mask = true;
+ }
+ if (!have_rcu_nocb_mask)
+ return;
+
+#ifdef CONFIG_RCU_NOCB_CPU_ZERO
+ pr_info("\tOffload RCU callbacks from CPU 0\n");
+ cpumask_set_cpu(0, rcu_nocb_mask);
+#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
+#ifdef CONFIG_RCU_NOCB_CPU_ALL
+ pr_info("\tOffload RCU callbacks from all CPUs\n");
+ cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
+#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
+#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=' contains nonexistent CPUs.\n");
+ cpumask_and(rcu_nocb_mask, cpu_possible_mask,
+ rcu_nocb_mask);
+ }
+ 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_rcu_flavor(rsp) {
+ for_each_cpu(cpu, rcu_nocb_mask)
+ init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu));
+ rcu_organize_nocb_kthreads(rsp);
+ }
+}
+
+/* Initialize per-rcu_data variables for no-CBs CPUs. */
+static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
+{
+ rdp->nocb_tail = &rdp->nocb_head;
+ init_swait_head(&rdp->nocb_wq);
+ rdp->nocb_follower_tail = &rdp->nocb_follower_head;
+}
+
+/*
+ * If the specified CPU is a no-CBs CPU that does not already have its
+ * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
+ * brought online out of order, this can require re-organizing the
+ * leader-follower relationships.
+ */
+static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu)
+{
+ struct rcu_data *rdp;
+ struct rcu_data *rdp_last;
+ struct rcu_data *rdp_old_leader;
+ struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu);
+ struct task_struct *t;
+
+ /*
+ * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
+ * then nothing to do.
+ */
+ if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread)
+ return;
+
+ /* If we didn't spawn the leader first, reorganize! */
+ rdp_old_leader = rdp_spawn->nocb_leader;
+ if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) {
+ rdp_last = NULL;
+ rdp = rdp_old_leader;
+ do {
+ rdp->nocb_leader = rdp_spawn;
+ if (rdp_last && rdp != rdp_spawn)
+ rdp_last->nocb_next_follower = rdp;
+ if (rdp == rdp_spawn) {
+ rdp = rdp->nocb_next_follower;
+ } else {
+ rdp_last = rdp;
+ rdp = rdp->nocb_next_follower;
+ rdp_last->nocb_next_follower = NULL;
+ }
+ } while (rdp);
+ rdp_spawn->nocb_next_follower = rdp_old_leader;
+ }
+
+ /* Spawn the kthread for this CPU and RCU flavor. */
+ t = kthread_run(rcu_nocb_kthread, rdp_spawn,
+ "rcuo%c/%d", rsp->abbr, cpu);
+ BUG_ON(IS_ERR(t));
+ ACCESS_ONCE(rdp_spawn->nocb_kthread) = t;
+}
+
+/*
+ * If the specified CPU is a no-CBs CPU that does not already have its
+ * rcuo kthreads, spawn them.
+ */
+static void rcu_spawn_all_nocb_kthreads(int cpu)
+{
+ struct rcu_state *rsp;
+
+ if (rcu_scheduler_fully_active)
+ for_each_rcu_flavor(rsp)
+ rcu_spawn_one_nocb_kthread(rsp, cpu);
+}
+
+/*
+ * Once the scheduler is running, spawn rcuo kthreads for all online
+ * no-CBs CPUs. This assumes that the early_initcall()s happen before
+ * non-boot CPUs come online -- if this changes, we will need to add
+ * some mutual exclusion.
+ */
+static void __init rcu_spawn_nocb_kthreads(void)
+{
+ int cpu;
+
+ for_each_online_cpu(cpu)
+ rcu_spawn_all_nocb_kthreads(cpu);
+}
+
+/* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
+static int rcu_nocb_leader_stride = -1;
+module_param(rcu_nocb_leader_stride, int, 0444);
+
+/*
+ * Initialize leader-follower relationships for all no-CBs CPU.
+ */
+static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
+{
+ int cpu;
+ int ls = rcu_nocb_leader_stride;
+ int nl = 0; /* Next leader. */
+ struct rcu_data *rdp;
+ struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */
+ struct rcu_data *rdp_prev = NULL;
+
+ if (!have_rcu_nocb_mask)
+ return;
+ if (ls == -1) {
+ ls = int_sqrt(nr_cpu_ids);
+ rcu_nocb_leader_stride = ls;
+ }
+
+ /*
+ * Each pass through this loop sets up one rcu_data structure and
+ * spawns one rcu_nocb_kthread().
+ */
+ for_each_cpu(cpu, rcu_nocb_mask) {
+ rdp = per_cpu_ptr(rsp->rda, cpu);
+ if (rdp->cpu >= nl) {
+ /* New leader, set up for followers & next leader. */
+ nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
+ rdp->nocb_leader = rdp;
+ rdp_leader = rdp;
+ } else {
+ /* Another follower, link to previous leader. */
+ rdp->nocb_leader = rdp_leader;
+ rdp_prev->nocb_next_follower = rdp;
+ }
+ rdp_prev = rdp;
+ }
+}
+
+/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
+static bool init_nocb_callback_list(struct rcu_data *rdp)
+{
+ if (!rcu_is_nocb_cpu(rdp->cpu))
+ return false;
+
+ /* If there are early-boot callbacks, move them to nocb lists. */
+ if (rdp->nxtlist) {
+ rdp->nocb_head = rdp->nxtlist;
+ rdp->nocb_tail = rdp->nxttail[RCU_NEXT_TAIL];
+ atomic_long_set(&rdp->nocb_q_count, rdp->qlen);
+ atomic_long_set(&rdp->nocb_q_count_lazy, rdp->qlen_lazy);
+ rdp->nxtlist = NULL;
+ rdp->qlen = 0;
+ rdp->qlen_lazy = 0;
+ }
+ rdp->nxttail[RCU_NEXT_TAIL] = NULL;
+ return true;
+}
+
+#else /* #ifdef CONFIG_RCU_NOCB_CPU */
+
+static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
+{
+ WARN_ON_ONCE(1); /* Should be dead code. */
+ return false;
+}
+
+static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+}
+
+static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
+{
+}
+
+static void rcu_init_one_nocb(struct rcu_node *rnp)
+{
+}
+
+static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
+ bool lazy, unsigned long flags)
+{
+ return false;
+}
+
+static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
+ struct rcu_data *rdp,
+ unsigned long flags)
+{
+ return false;
+}
+
+static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
+{
+}
+
+static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
+{
+ return false;
+}
+
+static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
+{
+}
+
+static void rcu_spawn_all_nocb_kthreads(int cpu)
+{
+}
+
+static void __init rcu_spawn_nocb_kthreads(void)
+{
+}
+
+static bool init_nocb_callback_list(struct rcu_data *rdp)
+{
+ return false;
+}
+
+#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
+
+/*
+ * An adaptive-ticks CPU can potentially execute in kernel mode for an
+ * arbitrarily long period of time with the scheduling-clock tick turned
+ * off. RCU will be paying attention to this CPU because it is in the
+ * kernel, but the CPU cannot be guaranteed to be executing the RCU state
+ * machine because the scheduling-clock tick has been disabled. Therefore,
+ * if an adaptive-ticks CPU is failing to respond to the current grace
+ * period and has not be idle from an RCU perspective, kick it.
+ */
+static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
+{
+#ifdef CONFIG_NO_HZ_FULL
+ if (tick_nohz_full_cpu(cpu))
+ smp_send_reschedule(cpu);
+#endif /* #ifdef CONFIG_NO_HZ_FULL */
+}
+
+
+#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
+
+static int full_sysidle_state; /* Current system-idle state. */
+#define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
+#define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
+#define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
+#define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
+#define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
+
+/*
+ * Invoked to note exit from irq or task transition to idle. Note that
+ * usermode execution does -not- count as idle here! After all, we want
+ * to detect full-system idle states, not RCU quiescent states and grace
+ * periods. The caller must have disabled interrupts.
+ */
+static void rcu_sysidle_enter(int irq)
+{
+ unsigned long j;
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+
+ /* If there are no nohz_full= CPUs, no need to track this. */
+ if (!tick_nohz_full_enabled())
+ return;
+
+ /* Adjust nesting, check for fully idle. */
+ if (irq) {
+ rdtp->dynticks_idle_nesting--;
+ WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
+ if (rdtp->dynticks_idle_nesting != 0)
+ return; /* Still not fully idle. */
+ } else {
+ if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
+ DYNTICK_TASK_NEST_VALUE) {
+ rdtp->dynticks_idle_nesting = 0;
+ } else {
+ rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
+ WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
+ return; /* Still not fully idle. */
+ }
+ }
+
+ /* Record start of fully idle period. */
+ j = jiffies;
+ ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
+ smp_mb__before_atomic();
+ atomic_inc(&rdtp->dynticks_idle);
+ smp_mb__after_atomic();
+ WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
+}
+
+/*
+ * Unconditionally force exit from full system-idle state. This is
+ * invoked when a normal CPU exits idle, but must be called separately
+ * for the timekeeping CPU (tick_do_timer_cpu). The reason for this
+ * is that the timekeeping CPU is permitted to take scheduling-clock
+ * interrupts while the system is in system-idle state, and of course
+ * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
+ * interrupt from any other type of interrupt.
+ */
+void rcu_sysidle_force_exit(void)
+{
+ int oldstate = ACCESS_ONCE(full_sysidle_state);
+ int newoldstate;
+
+ /*
+ * Each pass through the following loop attempts to exit full
+ * system-idle state. If contention proves to be a problem,
+ * a trylock-based contention tree could be used here.
+ */
+ while (oldstate > RCU_SYSIDLE_SHORT) {
+ newoldstate = cmpxchg(&full_sysidle_state,
+ oldstate, RCU_SYSIDLE_NOT);
+ if (oldstate == newoldstate &&
+ oldstate == RCU_SYSIDLE_FULL_NOTED) {
+ rcu_kick_nohz_cpu(tick_do_timer_cpu);
+ return; /* We cleared it, done! */
+ }
+ oldstate = newoldstate;
+ }
+ smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
+}
+
+/*
+ * Invoked to note entry to irq or task transition from idle. Note that
+ * usermode execution does -not- count as idle here! The caller must
+ * have disabled interrupts.
+ */
+static void rcu_sysidle_exit(int irq)
+{
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+
+ /* If there are no nohz_full= CPUs, no need to track this. */
+ if (!tick_nohz_full_enabled())
+ return;
+
+ /* Adjust nesting, check for already non-idle. */
+ if (irq) {
+ rdtp->dynticks_idle_nesting++;
+ WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
+ if (rdtp->dynticks_idle_nesting != 1)
+ return; /* Already non-idle. */
+ } else {
+ /*
+ * Allow for irq misnesting. Yes, it really is possible
+ * to enter an irq handler then never leave it, and maybe
+ * also vice versa. Handle both possibilities.
+ */
+ if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
+ rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
+ WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
+ return; /* Already non-idle. */
+ } else {
+ rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
+ }
+ }
+
+ /* Record end of idle period. */
+ smp_mb__before_atomic();
+ atomic_inc(&rdtp->dynticks_idle);
+ smp_mb__after_atomic();
+ WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
+
+ /*
+ * If we are the timekeeping CPU, we are permitted to be non-idle
+ * during a system-idle state. This must be the case, because
+ * the timekeeping CPU has to take scheduling-clock interrupts
+ * during the time that the system is transitioning to full
+ * system-idle state. This means that the timekeeping CPU must
+ * invoke rcu_sysidle_force_exit() directly if it does anything
+ * more than take a scheduling-clock interrupt.
+ */
+ if (smp_processor_id() == tick_do_timer_cpu)
+ return;
+
+ /* Update system-idle state: We are clearly no longer fully idle! */
+ rcu_sysidle_force_exit();
+}
+
+/*
+ * Check to see if the current CPU is idle. Note that usermode execution
+ * does not count as idle. The caller must have disabled interrupts,
+ * and must be running on tick_do_timer_cpu.
+ */
+static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
+ unsigned long *maxj)
+{
+ int cur;
+ unsigned long j;
+ struct rcu_dynticks *rdtp = rdp->dynticks;
+
+ /* If there are no nohz_full= CPUs, don't check system-wide idleness. */
+ if (!tick_nohz_full_enabled())
+ return;
+
+ /*
+ * If some other CPU has already reported non-idle, if this is
+ * not the flavor of RCU that tracks sysidle state, or if this
+ * is an offline or the timekeeping CPU, nothing to do.
+ */
+ if (!*isidle || rdp->rsp != rcu_state_p ||
+ cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
+ return;
+ /* Verify affinity of current kthread. */
+ WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
+
+ /* Pick up current idle and NMI-nesting counter and check. */
+ cur = atomic_read(&rdtp->dynticks_idle);
+ if (cur & 0x1) {
+ *isidle = false; /* We are not idle! */
+ return;
+ }
+ smp_mb(); /* Read counters before timestamps. */
+
+ /* Pick up timestamps. */
+ j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
+ /* If this CPU entered idle more recently, update maxj timestamp. */
+ if (ULONG_CMP_LT(*maxj, j))
+ *maxj = j;
+}
+
+/*
+ * Is this the flavor of RCU that is handling full-system idle?
+ */
+static bool is_sysidle_rcu_state(struct rcu_state *rsp)
+{
+ return rsp == rcu_state_p;
+}
+
+/*
+ * Return a delay in jiffies based on the number of CPUs, rcu_node
+ * leaf fanout, and jiffies tick rate. The idea is to allow larger
+ * systems more time to transition to full-idle state in order to
+ * avoid the cache thrashing that otherwise occur on the state variable.
+ * Really small systems (less than a couple of tens of CPUs) should
+ * instead use a single global atomically incremented counter, and later
+ * versions of this will automatically reconfigure themselves accordingly.
+ */
+static unsigned long rcu_sysidle_delay(void)
+{
+ if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
+ return 0;
+ return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
+}
+
+/*
+ * Advance the full-system-idle state. This is invoked when all of
+ * the non-timekeeping CPUs are idle.
+ */
+static void rcu_sysidle(unsigned long j)
+{
+ /* Check the current state. */
+ switch (ACCESS_ONCE(full_sysidle_state)) {
+ case RCU_SYSIDLE_NOT:
+
+ /* First time all are idle, so note a short idle period. */
+ ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT;
+ break;
+
+ case RCU_SYSIDLE_SHORT:
+
+ /*
+ * Idle for a bit, time to advance to next state?
+ * cmpxchg failure means race with non-idle, let them win.
+ */
+ if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
+ (void)cmpxchg(&full_sysidle_state,
+ RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
+ break;
+
+ case RCU_SYSIDLE_LONG:
+
+ /*
+ * Do an additional check pass before advancing to full.
+ * cmpxchg failure means race with non-idle, let them win.
+ */
+ if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
+ (void)cmpxchg(&full_sysidle_state,
+ RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
+ break;
+
+ default:
+ break;
+ }
+}
+
+/*
+ * Found a non-idle non-timekeeping CPU, so kick the system-idle state
+ * back to the beginning.
+ */
+static void rcu_sysidle_cancel(void)
+{
+ smp_mb();
+ if (full_sysidle_state > RCU_SYSIDLE_SHORT)
+ ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
+}
+
+/*
+ * Update the sysidle state based on the results of a force-quiescent-state
+ * scan of the CPUs' dyntick-idle state.
+ */
+static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
+ unsigned long maxj, bool gpkt)
+{
+ if (rsp != rcu_state_p)
+ return; /* Wrong flavor, ignore. */
+ if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
+ return; /* Running state machine from timekeeping CPU. */
+ if (isidle)
+ rcu_sysidle(maxj); /* More idle! */
+ else
+ rcu_sysidle_cancel(); /* Idle is over. */
+}
+
+/*
+ * Wrapper for rcu_sysidle_report() when called from the grace-period
+ * kthread's context.
+ */
+static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
+ unsigned long maxj)
+{
+ /* If there are no nohz_full= CPUs, no need to track this. */
+ if (!tick_nohz_full_enabled())
+ return;
+
+ rcu_sysidle_report(rsp, isidle, maxj, true);
+}
+
+/* Callback and function for forcing an RCU grace period. */
+struct rcu_sysidle_head {
+ struct rcu_head rh;
+ int inuse;
+};
+
+static void rcu_sysidle_cb(struct rcu_head *rhp)
+{
+ struct rcu_sysidle_head *rshp;
+
+ /*
+ * The following memory barrier is needed to replace the
+ * memory barriers that would normally be in the memory
+ * allocator.
+ */
+ smp_mb(); /* grace period precedes setting inuse. */
+
+ rshp = container_of(rhp, struct rcu_sysidle_head, rh);
+ ACCESS_ONCE(rshp->inuse) = 0;
+}
+
+/*
+ * Check to see if the system is fully idle, other than the timekeeping CPU.
+ * The caller must have disabled interrupts. This is not intended to be
+ * called unless tick_nohz_full_enabled().
+ */
+bool rcu_sys_is_idle(void)
+{
+ static struct rcu_sysidle_head rsh;
+ int rss = ACCESS_ONCE(full_sysidle_state);
+
+ if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
+ return false;
+
+ /* Handle small-system case by doing a full scan of CPUs. */
+ if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
+ int oldrss = rss - 1;
+
+ /*
+ * One pass to advance to each state up to _FULL.
+ * Give up if any pass fails to advance the state.
+ */
+ while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
+ int cpu;
+ bool isidle = true;
+ unsigned long maxj = jiffies - ULONG_MAX / 4;
+ struct rcu_data *rdp;
+
+ /* Scan all the CPUs looking for nonidle CPUs. */
+ for_each_possible_cpu(cpu) {
+ rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
+ rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
+ if (!isidle)
+ break;
+ }
+ rcu_sysidle_report(rcu_state_p, isidle, maxj, false);
+ oldrss = rss;
+ rss = ACCESS_ONCE(full_sysidle_state);
+ }
+ }
+
+ /* If this is the first observation of an idle period, record it. */
+ if (rss == RCU_SYSIDLE_FULL) {
+ rss = cmpxchg(&full_sysidle_state,
+ RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
+ return rss == RCU_SYSIDLE_FULL;
+ }
+
+ smp_mb(); /* ensure rss load happens before later caller actions. */
+
+ /* If already fully idle, tell the caller (in case of races). */
+ if (rss == RCU_SYSIDLE_FULL_NOTED)
+ return true;
+
+ /*
+ * If we aren't there yet, and a grace period is not in flight,
+ * initiate a grace period. Either way, tell the caller that
+ * we are not there yet. We use an xchg() rather than an assignment
+ * to make up for the memory barriers that would otherwise be
+ * provided by the memory allocator.
+ */
+ if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
+ !rcu_gp_in_progress(rcu_state_p) &&
+ !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
+ call_rcu(&rsh.rh, rcu_sysidle_cb);
+ return false;
+}
+
+/*
+ * Initialize dynticks sysidle state for CPUs coming online.
+ */
+static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
+{
+ rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
+}
+
+#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
+
+static void rcu_sysidle_enter(int irq)
+{
+}
+
+static void rcu_sysidle_exit(int irq)
+{
+}
+
+static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
+ unsigned long *maxj)
+{
+}
+
+static bool is_sysidle_rcu_state(struct rcu_state *rsp)
+{
+ return false;
+}
+
+static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
+ unsigned long maxj)
+{
+}
+
+static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
+{
+}
+
+#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
+
+/*
+ * 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(struct rcu_state *rsp)
+{
+#ifdef CONFIG_NO_HZ_FULL
+ if (tick_nohz_full_cpu(smp_processor_id()) &&
+ (!rcu_gp_in_progress(rsp) ||
+ ULONG_CMP_LT(jiffies, ACCESS_ONCE(rsp->gp_start) + HZ)))
+ return 1;
+#endif /* #ifdef CONFIG_NO_HZ_FULL */
+ return 0;
+}
+
+/*
+ * Bind the grace-period kthread for the sysidle flavor of RCU to the
+ * timekeeping CPU.
+ */
+static void rcu_bind_gp_kthread(void)
+{
+ int __maybe_unused cpu;
+
+ if (!tick_nohz_full_enabled())
+ return;
+#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
+ cpu = tick_do_timer_cpu;
+ if (cpu >= 0 && cpu < nr_cpu_ids)
+ set_cpus_allowed_ptr(current, cpumask_of(cpu));
+#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
+ housekeeping_affine(current);
+#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
+}
+
+/* Record the current task on dyntick-idle entry. */
+static void rcu_dynticks_task_enter(void)
+{
+#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
+ ACCESS_ONCE(current->rcu_tasks_idle_cpu) = smp_processor_id();
+#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
+}
+
+/* Record no current task on dyntick-idle exit. */
+static void rcu_dynticks_task_exit(void)
+{
+#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
+ ACCESS_ONCE(current->rcu_tasks_idle_cpu) = -1;
+#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
+}
Code Review / kvmfornfv.git / blobdiff