tree_plugin.h 93.4 KB
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/*
 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
 * Internal non-public definitions that provide either classic
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 * or preemptible semantics.
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 *
 * 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
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 * along with this program; if not, you can access it online at
 * http://www.gnu.org/licenses/gpl-2.0.html.
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 *
 * Copyright Red Hat, 2009
 * Copyright IBM Corporation, 2009
 *
 * Author: Ingo Molnar <mingo@elte.hu>
 *	   Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 */

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#include <linux/delay.h>
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#include <linux/gfp.h>
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#include <linux/oom.h>
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#include <linux/smpboot.h>
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#include "../time/tick-internal.h"
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#define RCU_KTHREAD_PRIO 1

#ifdef CONFIG_RCU_BOOST
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#include "../locking/rtmutex_common.h"
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#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
#else
#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
#endif

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#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? */
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static bool __read_mostly rcu_nocb_poll;    /* Offload kthread are to poll. */
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static char __initdata nocb_buf[NR_CPUS * 5];
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */

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/*
 * 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)
{
#ifdef CONFIG_RCU_TRACE
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	pr_info("\tRCU debugfs-based tracing is enabled.\n");
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#endif
#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
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	pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
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	       CONFIG_RCU_FANOUT);
#endif
#ifdef CONFIG_RCU_FANOUT_EXACT
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	pr_info("\tHierarchical RCU autobalancing is disabled.\n");
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#endif
#ifdef CONFIG_RCU_FAST_NO_HZ
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	pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
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#endif
#ifdef CONFIG_PROVE_RCU
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	pr_info("\tRCU lockdep checking is enabled.\n");
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#endif
#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
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	pr_info("\tRCU torture testing starts during boot.\n");
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#endif
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#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
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	pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n");
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#endif
#if defined(CONFIG_RCU_CPU_STALL_INFO)
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	pr_info("\tAdditional per-CPU info printed with stalls.\n");
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#endif
#if NUM_RCU_LVL_4 != 0
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	pr_info("\tFour-level hierarchy is enabled.\n");
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#endif
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	if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
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		pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
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	if (nr_cpu_ids != NR_CPUS)
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		pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
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}

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#ifdef CONFIG_TREE_PREEMPT_RCU

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RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
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static struct rcu_state *rcu_state_p = &rcu_preempt_state;
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static int rcu_preempted_readers_exp(struct rcu_node *rnp);

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/*
 * Tell them what RCU they are running.
 */
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static void __init rcu_bootup_announce(void)
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{
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	pr_info("Preemptible hierarchical RCU implementation.\n");
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	rcu_bootup_announce_oddness();
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}

/*
 * Return the number of RCU-preempt batches processed thus far
 * for debug and statistics.
 */
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static long rcu_batches_completed_preempt(void)
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{
	return rcu_preempt_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);

/*
 * Return the number of RCU batches processed thus far for debug & stats.
 */
long rcu_batches_completed(void)
{
	return rcu_batches_completed_preempt();
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);

/*
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 * Record a preemptible-RCU quiescent state for the specified CPU.  Note
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 * 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.
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 *
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 * As with the other rcu_*_qs() functions, callers to this function
 * must disable preemption.
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 */
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static void rcu_preempt_qs(void)
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{
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	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;
	}
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}

/*
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 * 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
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 * 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.
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 *
 * Caller must disable preemption.
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 */
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static void rcu_preempt_note_context_switch(int cpu)
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{
	struct task_struct *t = current;
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	unsigned long flags;
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	struct rcu_data *rdp;
	struct rcu_node *rnp;

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	if (t->rcu_read_lock_nesting > 0 &&
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	    !t->rcu_read_unlock_special.b.blocked) {
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		/* Possibly blocking in an RCU read-side critical section. */
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		rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
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		rnp = rdp->mynode;
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		raw_spin_lock_irqsave(&rnp->lock, flags);
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		smp_mb__after_unlock_lock();
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		t->rcu_read_unlock_special.b.blocked = true;
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		t->rcu_blocked_node = rnp;
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		/*
		 * 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
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		 * 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!!!
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		 *
		 * But first, note that the current CPU must still be
		 * on line!
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		 */
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		WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
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		WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
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		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;
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#ifdef CONFIG_RCU_BOOST
			if (rnp->boost_tasks != NULL)
				rnp->boost_tasks = rnp->gp_tasks;
#endif /* #ifdef CONFIG_RCU_BOOST */
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		} else {
			list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
			if (rnp->qsmask & rdp->grpmask)
				rnp->gp_tasks = &t->rcu_node_entry;
		}
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		trace_rcu_preempt_task(rdp->rsp->name,
				       t->pid,
				       (rnp->qsmask & rdp->grpmask)
				       ? rnp->gpnum
				       : rnp->gpnum + 1);
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		raw_spin_unlock_irqrestore(&rnp->lock, flags);
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	} else if (t->rcu_read_lock_nesting < 0 &&
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		   t->rcu_read_unlock_special.s) {
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		/*
		 * Complete exit from RCU read-side critical section on
		 * behalf of preempted instance of __rcu_read_unlock().
		 */
		rcu_read_unlock_special(t);
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	}

	/*
	 * 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.
	 */
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	rcu_preempt_qs();
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}

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/*
 * 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.
 */
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static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
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{
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	return rnp->gp_tasks != NULL;
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}

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/*
 * Record a quiescent state for all tasks that were previously queued
 * on the specified rcu_node structure and that were blocking the current
 * RCU grace period.  The caller must hold the specified rnp->lock with
 * irqs disabled, and this lock is released upon return, but irqs remain
 * disabled.
 */
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static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
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	__releases(rnp->lock)
{
	unsigned long mask;
	struct rcu_node *rnp_p;

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	if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
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		raw_spin_unlock_irqrestore(&rnp->lock, flags);
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		return;  /* Still need more quiescent states! */
	}

	rnp_p = rnp->parent;
	if (rnp_p == NULL) {
		/*
		 * Either there is only one rcu_node in the tree,
		 * or tasks were kicked up to root rcu_node due to
		 * CPUs going offline.
		 */
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		rcu_report_qs_rsp(&rcu_preempt_state, flags);
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		return;
	}

	/* Report up the rest of the hierarchy. */
	mask = rnp->grpmask;
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	raw_spin_unlock(&rnp->lock);	/* irqs remain disabled. */
	raw_spin_lock(&rnp_p->lock);	/* irqs already disabled. */
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	smp_mb__after_unlock_lock();
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	rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
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}

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/*
 * 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;
}

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/*
 * 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.
 */
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void rcu_read_unlock_special(struct task_struct *t)
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{
	int empty;
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	int empty_exp;
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	int empty_exp_now;
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	unsigned long flags;
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	struct list_head *np;
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#ifdef CONFIG_RCU_BOOST
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	bool drop_boost_mutex = false;
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#endif /* #ifdef CONFIG_RCU_BOOST */
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	struct rcu_node *rnp;
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	union rcu_special special;
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	/* 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,
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	 * let it know that we have done so.  Because irqs are disabled,
	 * t->rcu_read_unlock_special cannot change.
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	 */
	special = t->rcu_read_unlock_special;
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	if (special.b.need_qs) {
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		rcu_preempt_qs();
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		if (!t->rcu_read_unlock_special.s) {
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			local_irq_restore(flags);
			return;
		}
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	}

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	/* Hardware IRQ handlers cannot block, complain if they get here. */
	if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) {
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		local_irq_restore(flags);
		return;
	}

	/* Clean up if blocked during RCU read-side critical section. */
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	if (special.b.blocked) {
		t->rcu_read_unlock_special.b.blocked = false;
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		/*
		 * 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 (;;) {
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			rnp = t->rcu_blocked_node;
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			raw_spin_lock(&rnp->lock);  /* irqs already disabled. */
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			smp_mb__after_unlock_lock();
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			if (rnp == t->rcu_blocked_node)
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				break;
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			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
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		}
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		empty = !rcu_preempt_blocked_readers_cgp(rnp);
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		empty_exp = !rcu_preempted_readers_exp(rnp);
		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
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		np = rcu_next_node_entry(t, rnp);
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		list_del_init(&t->rcu_node_entry);
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		t->rcu_blocked_node = NULL;
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		trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
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						rnp->gpnum, t->pid);
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		if (&t->rcu_node_entry == rnp->gp_tasks)
			rnp->gp_tasks = np;
		if (&t->rcu_node_entry == rnp->exp_tasks)
			rnp->exp_tasks = np;
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#ifdef CONFIG_RCU_BOOST
		if (&t->rcu_node_entry == rnp->boost_tasks)
			rnp->boost_tasks = np;
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		/* Snapshot ->boost_mtx ownership with rcu_node lock held. */
		drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
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#endif /* #ifdef CONFIG_RCU_BOOST */
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		/*
		 * If this was the last task on the current list, and if
		 * we aren't waiting on any CPUs, report the quiescent state.
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		 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
		 * so we must take a snapshot of the expedited state.
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		 */
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		empty_exp_now = !rcu_preempted_readers_exp(rnp);
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		if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
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			trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
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							 rnp->gpnum,
							 0, rnp->qsmask,
							 rnp->level,
							 rnp->grplo,
							 rnp->grphi,
							 !!rnp->gp_tasks);
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			rcu_report_unblock_qs_rnp(rnp, flags);
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		} else {
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			raw_spin_unlock_irqrestore(&rnp->lock, flags);
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		}
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#ifdef CONFIG_RCU_BOOST
		/* Unboost if we were boosted. */
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		if (drop_boost_mutex) {
			rt_mutex_unlock(&rnp->boost_mtx);
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			complete(&rnp->boost_completion);
		}
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#endif /* #ifdef CONFIG_RCU_BOOST */

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		/*
		 * If this was the last task on the expedited lists,
		 * then we need to report up the rcu_node hierarchy.
		 */
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		if (!empty_exp && empty_exp_now)
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			rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
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	} else {
		local_irq_restore(flags);
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	}
}

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#ifdef CONFIG_RCU_CPU_STALL_VERBOSE

/*
 * 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;

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	raw_spin_lock_irqsave(&rnp->lock, flags);
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	if (!rcu_preempt_blocked_readers_cgp(rnp)) {
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		return;
	}
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	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);
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}

/*
 * 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);
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */

static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */

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#ifdef CONFIG_RCU_CPU_STALL_INFO

static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
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	pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
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	       rnp->level, rnp->grplo, rnp->grphi);
}

static void rcu_print_task_stall_end(void)
{
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	pr_cont("\n");
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}

#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 */

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/*
 * Scan the current list of tasks blocked within RCU read-side critical
 * sections, printing out the tid of each.
 */
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static int rcu_print_task_stall(struct rcu_node *rnp)
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{
	struct task_struct *t;
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	int ndetected = 0;
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	if (!rcu_preempt_blocked_readers_cgp(rnp))
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		return 0;
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	rcu_print_task_stall_begin(rnp);
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	t = list_entry(rnp->gp_tasks,
		       struct task_struct, rcu_node_entry);
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	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
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		pr_cont(" P%d", t->pid);
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		ndetected++;
	}
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	rcu_print_task_stall_end();
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	return ndetected;
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}

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/*
 * 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.
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 *
 * Also, if there are blocked tasks on the list, they automatically
 * block the newly created grace period, so set up ->gp_tasks accordingly.
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 */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
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	WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
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	if (!list_empty(&rnp->blkd_tasks))
		rnp->gp_tasks = rnp->blkd_tasks.next;
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	WARN_ON_ONCE(rnp->qsmask);
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}

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#ifdef CONFIG_HOTPLUG_CPU

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/*
 * Handle tasklist migration for case in which all CPUs covered by the
 * specified rcu_node have gone offline.  Move them up to the root
 * rcu_node.  The reason for not just moving them to the immediate
 * parent is to remove the need for rcu_read_unlock_special() to
 * make more than two attempts to acquire the target rcu_node's lock.
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 * Returns true if there were tasks blocking the current RCU grace
 * period.
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 *
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 * Returns 1 if there was previously a task blocking the current grace
 * period on the specified rcu_node structure.
 *
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 * The caller must hold rnp->lock with irqs disabled.
 */
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static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
				     struct rcu_node *rnp,
				     struct rcu_data *rdp)
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{
	struct list_head *lp;
	struct list_head *lp_root;
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	int retval = 0;
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	struct rcu_node *rnp_root = rcu_get_root(rsp);
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	struct task_struct *t;
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	if (rnp == rnp_root) {
		WARN_ONCE(1, "Last CPU thought to be offlined?");
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		return 0;  /* Shouldn't happen: at least one CPU online. */
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	}
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	/* If we are on an internal node, complain bitterly. */
	WARN_ON_ONCE(rnp != rdp->mynode);
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	/*
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	 * Move tasks up to root rcu_node.  Don't try to get fancy for
	 * this corner-case operation -- just put this node's tasks
	 * at the head of the root node's list, and update the root node's
	 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
	 * if non-NULL.  This might result in waiting for more tasks than
	 * absolutely necessary, but this is a good performance/complexity
	 * tradeoff.
569
	 */
570
	if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
571 572 573
		retval |= RCU_OFL_TASKS_NORM_GP;
	if (rcu_preempted_readers_exp(rnp))
		retval |= RCU_OFL_TASKS_EXP_GP;
574 575 576 577 578
	lp = &rnp->blkd_tasks;
	lp_root = &rnp_root->blkd_tasks;
	while (!list_empty(lp)) {
		t = list_entry(lp->next, typeof(*t), rcu_node_entry);
		raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
579
		smp_mb__after_unlock_lock();
580 581 582 583 584 585 586
		list_del(&t->rcu_node_entry);
		t->rcu_blocked_node = rnp_root;
		list_add(&t->rcu_node_entry, lp_root);
		if (&t->rcu_node_entry == rnp->gp_tasks)
			rnp_root->gp_tasks = rnp->gp_tasks;
		if (&t->rcu_node_entry == rnp->exp_tasks)
			rnp_root->exp_tasks = rnp->exp_tasks;
587 588 589 590
#ifdef CONFIG_RCU_BOOST
		if (&t->rcu_node_entry == rnp->boost_tasks)
			rnp_root->boost_tasks = rnp->boost_tasks;
#endif /* #ifdef CONFIG_RCU_BOOST */
591
		raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
592
	}
593

594 595
	rnp->gp_tasks = NULL;
	rnp->exp_tasks = NULL;
596
#ifdef CONFIG_RCU_BOOST
597
	rnp->boost_tasks = NULL;
598 599 600 601 602
	/*
	 * In case root is being boosted and leaf was not.  Make sure
	 * that we boost the tasks blocking the current grace period
	 * in this case.
	 */
603
	raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
604
	smp_mb__after_unlock_lock();
605
	if (rnp_root->boost_tasks != NULL &&
606 607
	    rnp_root->boost_tasks != rnp_root->gp_tasks &&
	    rnp_root->boost_tasks != rnp_root->exp_tasks)
608 609 610 611
		rnp_root->boost_tasks = rnp_root->gp_tasks;
	raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
#endif /* #ifdef CONFIG_RCU_BOOST */

612
	return retval;
613 614
}

615 616
#endif /* #ifdef CONFIG_HOTPLUG_CPU */

617 618 619 620 621 622 623
/*
 * 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.
 */
624
static void rcu_preempt_check_callbacks(void)
625 626 627 628
{
	struct task_struct *t = current;

	if (t->rcu_read_lock_nesting == 0) {
629
		rcu_preempt_qs();
630 631
		return;
	}
632
	if (t->rcu_read_lock_nesting > 0 &&
633 634
	    __this_cpu_read(rcu_preempt_data.qs_pending) &&
	    !__this_cpu_read(rcu_preempt_data.passed_quiesce))
635
		t->rcu_read_unlock_special.b.need_qs = true;
636 637
}

638 639
#ifdef CONFIG_RCU_BOOST

640 641
static void rcu_preempt_do_callbacks(void)
{
642
	rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
643 644
}

645 646
#endif /* #ifdef CONFIG_RCU_BOOST */

647
/*
P
Paul E. McKenney 已提交
648
 * Queue a preemptible-RCU callback for invocation after a grace period.
649 650 651
 */
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
P
Paul E. McKenney 已提交
652
	__call_rcu(head, func, &rcu_preempt_state, -1, 0);
653 654 655
}
EXPORT_SYMBOL_GPL(call_rcu);

656 657 658 659 660
/**
 * 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
661 662 663 664 665
 * 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.
666 667 668
 *
 * See the description of synchronize_sched() for more detailed information
 * on memory ordering guarantees.
669 670 671
 */
void synchronize_rcu(void)
{
672 673 674 675
	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");
676 677
	if (!rcu_scheduler_active)
		return;
678 679 680 681
	if (rcu_expedited)
		synchronize_rcu_expedited();
	else
		wait_rcu_gp(call_rcu);
682 683 684
}
EXPORT_SYMBOL_GPL(synchronize_rcu);

685
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
686
static unsigned long sync_rcu_preempt_exp_count;
687 688 689 690 691 692 693 694 695 696
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)
{
697
	return rnp->exp_tasks != NULL;
698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722
}

/*
 * 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!)
 *
723 724 725
 * Most callers will set the "wake" flag, but the task initiating the
 * expedited grace period need not wake itself.
 *
726 727
 * Caller must hold sync_rcu_preempt_exp_mutex.
 */
728 729
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
			       bool wake)
730 731 732 733
{
	unsigned long flags;
	unsigned long mask;

P
Paul E. McKenney 已提交
734
	raw_spin_lock_irqsave(&rnp->lock, flags);
735
	smp_mb__after_unlock_lock();
736
	for (;;) {
737 738
		if (!sync_rcu_preempt_exp_done(rnp)) {
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
739
			break;
740
		}
741
		if (rnp->parent == NULL) {
742
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
743 744
			if (wake) {
				smp_mb(); /* EGP done before wake_up(). */
745
				wake_up(&sync_rcu_preempt_exp_wq);
746
			}
747 748 749
			break;
		}
		mask = rnp->grpmask;
P
Paul E. McKenney 已提交
750
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
751
		rnp = rnp->parent;
P
Paul E. McKenney 已提交
752
		raw_spin_lock(&rnp->lock); /* irqs already disabled */
753
		smp_mb__after_unlock_lock();
754 755 756 757 758 759 760 761 762
		rnp->expmask &= ~mask;
	}
}

/*
 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
 * grace period for the specified rcu_node structure.  If there are no such
 * tasks, report it up the rcu_node hierarchy.
 *
763 764
 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
 * CPU hotplug operations.
765 766 767 768
 */
static void
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
{
769
	unsigned long flags;
770
	int must_wait = 0;
771

772
	raw_spin_lock_irqsave(&rnp->lock, flags);
773
	smp_mb__after_unlock_lock();
774
	if (list_empty(&rnp->blkd_tasks)) {
775
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
776
	} else {
777
		rnp->exp_tasks = rnp->blkd_tasks.next;
778
		rcu_initiate_boost(rnp, flags);  /* releases rnp->lock */
779 780
		must_wait = 1;
	}
781
	if (!must_wait)
782
		rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
783 784
}

785 786 787 788 789 790 791 792 793 794 795
/**
 * 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.
796 797 798
 */
void synchronize_rcu_expedited(void)
{
799 800 801
	unsigned long flags;
	struct rcu_node *rnp;
	struct rcu_state *rsp = &rcu_preempt_state;
802
	unsigned long snap;
803 804 805 806 807 808
	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. */

809 810 811 812 813 814 815 816
	/*
	 * 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.
	 */
817 818 819 820 821
	if (!try_get_online_cpus()) {
		/* CPU-hotplug operation in flight, fall back to normal GP. */
		wait_rcu_gp(call_rcu);
		return;
	}
822

823 824 825 826 827 828
	/*
	 * 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)) {
829 830 831 832 833
		if (ULONG_CMP_LT(snap,
		    ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
			put_online_cpus();
			goto mb_ret; /* Others did our work for us. */
		}
834
		if (trycount++ < 10) {
835
			udelay(trycount * num_online_cpus());
836
		} else {
837
			put_online_cpus();
838
			wait_rcu_gp(call_rcu);
839 840 841
			return;
		}
	}
842 843
	if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
		put_online_cpus();
844
		goto unlock_mb_ret; /* Others did our work for us. */
845
	}
846

847
	/* force all RCU readers onto ->blkd_tasks lists. */
848 849 850 851
	synchronize_sched_expedited();

	/* Initialize ->expmask for all non-leaf rcu_node structures. */
	rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
852
		raw_spin_lock_irqsave(&rnp->lock, flags);
853
		smp_mb__after_unlock_lock();
854
		rnp->expmask = rnp->qsmaskinit;
855
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
856 857
	}

858
	/* Snapshot current state of ->blkd_tasks lists. */
859 860 861 862 863
	rcu_for_each_leaf_node(rsp, rnp)
		sync_rcu_preempt_exp_init(rsp, rnp);
	if (NUM_RCU_NODES > 1)
		sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));

864
	put_online_cpus();
865

866
	/* Wait for snapshotted ->blkd_tasks lists to drain. */
867 868 869 870 871 872
	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. */
873 874
	ACCESS_ONCE(sync_rcu_preempt_exp_count) =
					sync_rcu_preempt_exp_count + 1;
875 876 877 878
unlock_mb_ret:
	mutex_unlock(&sync_rcu_preempt_exp_mutex);
mb_ret:
	smp_mb(); /* ensure subsequent action seen after grace period. */
879 880 881
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

882 883
/**
 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
884 885 886 887 888
 *
 * 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.
889 890 891
 */
void rcu_barrier(void)
{
892
	_rcu_barrier(&rcu_preempt_state);
893 894 895
}
EXPORT_SYMBOL_GPL(rcu_barrier);

896
/*
P
Paul E. McKenney 已提交
897
 * Initialize preemptible RCU's state structures.
898 899 900
 */
static void __init __rcu_init_preempt(void)
{
901
	rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
902 903
}

904 905 906 907 908 909 910 911 912 913 914 915 916 917
/*
 * 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(&current->rcu_node_entry)))
		return;
	t->rcu_read_lock_nesting = 1;
	barrier();
918
	t->rcu_read_unlock_special.b.blocked = true;
919 920 921
	__rcu_read_unlock();
}

922 923
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */

924
static struct rcu_state *rcu_state_p = &rcu_sched_state;
925

926 927 928
/*
 * Tell them what RCU they are running.
 */
929
static void __init rcu_bootup_announce(void)
930
{
931
	pr_info("Hierarchical RCU implementation.\n");
932
	rcu_bootup_announce_oddness();
933 934 935 936 937 938 939 940 941 942 943
}

/*
 * Return the number of RCU batches processed thus far for debug & stats.
 */
long rcu_batches_completed(void)
{
	return rcu_batches_completed_sched();
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);

944 945 946 947 948 949 950 951
/*
 * Because preemptible RCU does not exist, we never have to check for
 * CPUs being in quiescent states.
 */
static void rcu_preempt_note_context_switch(int cpu)
{
}

952
/*
P
Paul E. McKenney 已提交
953
 * Because preemptible RCU does not exist, there are never any preempted
954 955
 * RCU readers.
 */
956
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
957 958 959 960
{
	return 0;
}

961 962 963
#ifdef CONFIG_HOTPLUG_CPU

/* Because preemptible RCU does not exist, no quieting of tasks. */
P
Paul E. McKenney 已提交
964
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
965
	__releases(rnp->lock)
966
{
P
Paul E. McKenney 已提交
967
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
968 969 970 971
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

972
/*
P
Paul E. McKenney 已提交
973
 * Because preemptible RCU does not exist, we never have to check for
974 975 976 977 978 979
 * tasks blocked within RCU read-side critical sections.
 */
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}

980
/*
P
Paul E. McKenney 已提交
981
 * Because preemptible RCU does not exist, we never have to check for
982 983
 * tasks blocked within RCU read-side critical sections.
 */
984
static int rcu_print_task_stall(struct rcu_node *rnp)
985
{
986
	return 0;
987 988
}

989
/*
P
Paul E. McKenney 已提交
990
 * Because there is no preemptible RCU, there can be no readers blocked,
991 992
 * so there is no need to check for blocked tasks.  So check only for
 * bogus qsmask values.
993 994 995
 */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
996
	WARN_ON_ONCE(rnp->qsmask);
997 998
}

999 1000
#ifdef CONFIG_HOTPLUG_CPU

1001
/*
P
Paul E. McKenney 已提交
1002
 * Because preemptible RCU does not exist, it never needs to migrate
1003 1004 1005
 * tasks that were blocked within RCU read-side critical sections, and
 * such non-existent tasks cannot possibly have been blocking the current
 * grace period.
1006
 */
1007 1008 1009
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
				     struct rcu_node *rnp,
				     struct rcu_data *rdp)
1010
{
1011
	return 0;
1012 1013
}

1014 1015
#endif /* #ifdef CONFIG_HOTPLUG_CPU */

1016
/*
P
Paul E. McKenney 已提交
1017
 * Because preemptible RCU does not exist, it never has any callbacks
1018 1019
 * to check.
 */
1020
static void rcu_preempt_check_callbacks(void)
1021 1022 1023
{
}

1024 1025
/*
 * Wait for an rcu-preempt grace period, but make it happen quickly.
P
Paul E. McKenney 已提交
1026
 * But because preemptible RCU does not exist, map to rcu-sched.
1027 1028 1029 1030 1031 1032 1033
 */
void synchronize_rcu_expedited(void)
{
	synchronize_sched_expedited();
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

1034 1035 1036
#ifdef CONFIG_HOTPLUG_CPU

/*
P
Paul E. McKenney 已提交
1037
 * Because preemptible RCU does not exist, there is never any need to
1038 1039 1040
 * report on tasks preempted in RCU read-side critical sections during
 * expedited RCU grace periods.
 */
1041 1042
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
			       bool wake)
1043 1044 1045 1046 1047
{
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

1048
/*
P
Paul E. McKenney 已提交
1049
 * Because preemptible RCU does not exist, rcu_barrier() is just
1050 1051 1052 1053 1054 1055 1056 1057
 * another name for rcu_barrier_sched().
 */
void rcu_barrier(void)
{
	rcu_barrier_sched();
}
EXPORT_SYMBOL_GPL(rcu_barrier);

1058
/*
P
Paul E. McKenney 已提交
1059
 * Because preemptible RCU does not exist, it need not be initialized.
1060 1061 1062 1063 1064
 */
static void __init __rcu_init_preempt(void)
{
}

1065 1066 1067 1068 1069 1070 1071 1072
/*
 * Because preemptible RCU does not exist, tasks cannot possibly exit
 * while in preemptible RCU read-side critical sections.
 */
void exit_rcu(void)
{
}

1073
#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1074

1075 1076
#ifdef CONFIG_RCU_BOOST

1077
#include "../locking/rtmutex_common.h"
1078

1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091
#ifdef CONFIG_RCU_TRACE

static void rcu_initiate_boost_trace(struct rcu_node *rnp)
{
	if (list_empty(&rnp->blkd_tasks))
		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 &&
1092
		 ULONG_CMP_LT(jiffies, rnp->boost_time))
1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105
		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 */

T
Thomas Gleixner 已提交
1106 1107 1108 1109 1110 1111 1112 1113 1114 1115
static void rcu_wake_cond(struct task_struct *t, int status)
{
	/*
	 * If the thread is yielding, only wake it when this
	 * is invoked from idle
	 */
	if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
		wake_up_process(t);
}

1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133
/*
 * 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 (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
		return 0;  /* Nothing left to boost. */

	raw_spin_lock_irqsave(&rnp->lock, flags);
1134
	smp_mb__after_unlock_lock();
1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150

	/*
	 * 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.
	 */
1151
	if (rnp->exp_tasks != NULL) {
1152
		tb = rnp->exp_tasks;
1153 1154
		rnp->n_exp_boosts++;
	} else {
1155
		tb = rnp->boost_tasks;
1156 1157 1158
		rnp->n_normal_boosts++;
	}
	rnp->n_tasks_boosted++;
1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176

	/*
	 * 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);
1177
	rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
1178
	init_completion(&rnp->boost_completion);
1179
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1180 1181 1182
	/* 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. */
1183

1184
	/* Wait for boostee to be done w/boost_mtx before reinitializing. */
1185
	wait_for_completion(&rnp->boost_completion);
1186

1187 1188
	return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
	       ACCESS_ONCE(rnp->boost_tasks) != NULL;
1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200
}

/*
 * 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;

1201
	trace_rcu_utilization(TPS("Start boost kthread@init"));
1202
	for (;;) {
1203
		rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1204
		trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1205
		rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1206
		trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1207
		rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1208 1209 1210 1211 1212 1213
		more2boost = rcu_boost(rnp);
		if (more2boost)
			spincnt++;
		else
			spincnt = 0;
		if (spincnt > 10) {
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			rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1215
			trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
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1216
			schedule_timeout_interruptible(2);
1217
			trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1218 1219 1220
			spincnt = 0;
		}
	}
1221
	/* NOTREACHED */
1222
	trace_rcu_utilization(TPS("End boost kthread@notreached"));
1223 1224 1225 1226 1227 1228 1229 1230 1231
	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.
 *
1232 1233 1234
 * 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.
1235
 */
1236
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1237
	__releases(rnp->lock)
1238 1239 1240
{
	struct task_struct *t;

1241 1242
	if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
		rnp->n_balk_exp_gp_tasks++;
1243
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1244
		return;
1245
	}
1246 1247 1248 1249 1250 1251 1252
	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;
1253
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1254
		t = rnp->boost_kthread_task;
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1255 1256
		if (t)
			rcu_wake_cond(t, rnp->boost_kthread_status);
1257
	} else {
1258
		rcu_initiate_boost_trace(rnp);
1259 1260
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
	}
1261 1262
}

1263 1264 1265 1266 1267 1268 1269 1270 1271
/*
 * Wake up the per-CPU kthread to invoke RCU callbacks.
 */
static void invoke_rcu_callbacks_kthread(void)
{
	unsigned long flags;

	local_irq_save(flags);
	__this_cpu_write(rcu_cpu_has_work, 1);
1272
	if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
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1273 1274 1275 1276
	    current != __this_cpu_read(rcu_cpu_kthread_task)) {
		rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
			      __this_cpu_read(rcu_cpu_kthread_status));
	}
1277 1278 1279
	local_irq_restore(flags);
}

1280 1281 1282 1283 1284 1285
/*
 * Is the current CPU running the RCU-callbacks kthread?
 * Caller must have preemption disabled.
 */
static bool rcu_is_callbacks_kthread(void)
{
1286
	return __this_cpu_read(rcu_cpu_kthread_task) == current;
1287 1288
}

1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303
#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.
 */
1304
static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
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1305
						 struct rcu_node *rnp)
1306
{
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1307
	int rnp_index = rnp - &rsp->node[0];
1308 1309 1310 1311 1312 1313
	unsigned long flags;
	struct sched_param sp;
	struct task_struct *t;

	if (&rcu_preempt_state != rsp)
		return 0;
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1314 1315 1316 1317

	if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
		return 0;

1318
	rsp->boost = 1;
1319 1320 1321
	if (rnp->boost_kthread_task != NULL)
		return 0;
	t = kthread_create(rcu_boost_kthread, (void *)rnp,
1322
			   "rcub/%d", rnp_index);
1323 1324 1325
	if (IS_ERR(t))
		return PTR_ERR(t);
	raw_spin_lock_irqsave(&rnp->lock, flags);
1326
	smp_mb__after_unlock_lock();
1327 1328
	rnp->boost_kthread_task = t;
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1329
	sp.sched_priority = RCU_BOOST_PRIO;
1330
	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1331
	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1332 1333 1334
	return 0;
}

1335 1336
static void rcu_kthread_do_work(void)
{
1337 1338
	rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
	rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
1339 1340 1341
	rcu_preempt_do_callbacks();
}

1342
static void rcu_cpu_kthread_setup(unsigned int cpu)
1343 1344 1345
{
	struct sched_param sp;

1346 1347
	sp.sched_priority = RCU_KTHREAD_PRIO;
	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1348 1349
}

1350
static void rcu_cpu_kthread_park(unsigned int cpu)
1351
{
1352
	per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1353 1354
}

1355
static int rcu_cpu_kthread_should_run(unsigned int cpu)
1356
{
1357
	return __this_cpu_read(rcu_cpu_has_work);
1358 1359 1360 1361
}

/*
 * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
1362 1363
 * RCU softirq used in flavors and configurations of RCU that do not
 * support RCU priority boosting.
1364
 */
1365
static void rcu_cpu_kthread(unsigned int cpu)
1366
{
1367 1368
	unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
	char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
1369
	int spincnt;
1370

1371
	for (spincnt = 0; spincnt < 10; spincnt++) {
1372
		trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1373 1374
		local_bh_disable();
		*statusp = RCU_KTHREAD_RUNNING;
1375 1376
		this_cpu_inc(rcu_cpu_kthread_loops);
		local_irq_disable();
1377 1378
		work = *workp;
		*workp = 0;
1379
		local_irq_enable();
1380 1381 1382
		if (work)
			rcu_kthread_do_work();
		local_bh_enable();
1383
		if (*workp == 0) {
1384
			trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1385 1386
			*statusp = RCU_KTHREAD_WAITING;
			return;
1387 1388
		}
	}
1389
	*statusp = RCU_KTHREAD_YIELDING;
1390
	trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1391
	schedule_timeout_interruptible(2);
1392
	trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1393
	*statusp = RCU_KTHREAD_WAITING;
1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404
}

/*
 * 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.
 */
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static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1406
{
T
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1407 1408
	struct task_struct *t = rnp->boost_kthread_task;
	unsigned long mask = rnp->qsmaskinit;
1409 1410 1411
	cpumask_var_t cm;
	int cpu;

T
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1412
	if (!t)
1413
		return;
T
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1414
	if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1415 1416 1417 1418 1419 1420 1421 1422 1423 1424
		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);
		for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
			cpumask_clear_cpu(cpu, cm);
		WARN_ON_ONCE(cpumask_weight(cm) == 0);
	}
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1425
	set_cpus_allowed_ptr(t, cm);
1426 1427 1428
	free_cpumask_var(cm);
}

1429 1430 1431 1432 1433 1434 1435 1436
static struct smp_hotplug_thread rcu_cpu_thread_spec = {
	.store			= &rcu_cpu_kthread_task,
	.thread_should_run	= rcu_cpu_kthread_should_run,
	.thread_fn		= rcu_cpu_kthread,
	.thread_comm		= "rcuc/%u",
	.setup			= rcu_cpu_kthread_setup,
	.park			= rcu_cpu_kthread_park,
};
1437 1438

/*
1439
 * Spawn boost kthreads -- called as soon as the scheduler is running.
1440
 */
1441
static void __init rcu_spawn_boost_kthreads(void)
1442 1443
{
	struct rcu_node *rnp;
T
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1444
	int cpu;
1445

1446
	for_each_possible_cpu(cpu)
1447
		per_cpu(rcu_cpu_has_work, cpu) = 0;
1448
	BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1449 1450
	rnp = rcu_get_root(rcu_state_p);
	(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1451
	if (NUM_RCU_NODES > 1) {
1452 1453
		rcu_for_each_leaf_node(rcu_state_p, rnp)
			(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1454 1455 1456
	}
}

1457
static void rcu_prepare_kthreads(int cpu)
1458
{
1459
	struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
1460 1461 1462
	struct rcu_node *rnp = rdp->mynode;

	/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1463
	if (rcu_scheduler_fully_active)
1464
		(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1465 1466
}

1467 1468
#else /* #ifdef CONFIG_RCU_BOOST */

1469
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1470
	__releases(rnp->lock)
1471
{
1472
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1473 1474
}

1475
static void invoke_rcu_callbacks_kthread(void)
1476
{
1477
	WARN_ON_ONCE(1);
1478 1479
}

1480 1481 1482 1483 1484
static bool rcu_is_callbacks_kthread(void)
{
	return false;
}

1485 1486 1487 1488
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
}

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1489
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1490 1491 1492
{
}

1493
static void __init rcu_spawn_boost_kthreads(void)
1494 1495 1496
{
}

1497
static void rcu_prepare_kthreads(int cpu)
1498 1499 1500
{
}

1501 1502
#endif /* #else #ifdef CONFIG_RCU_BOOST */

1503 1504 1505 1506 1507 1508 1509 1510
#if !defined(CONFIG_RCU_FAST_NO_HZ)

/*
 * Check to see if any future RCU-related work will need to be done
 * by the current CPU, even if none need be done immediately, returning
 * 1 if so.  This function is part of the RCU implementation; it is -not-
 * an exported member of the RCU API.
 *
1511 1512
 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
 * any flavor of RCU.
1513
 */
1514
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1515
int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1516
{
1517
	*delta_jiffies = ULONG_MAX;
1518
	return rcu_cpu_has_callbacks(cpu, NULL);
1519
}
1520
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1521 1522 1523 1524 1525 1526 1527 1528 1529

/*
 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
 * after it.
 */
static void rcu_cleanup_after_idle(int cpu)
{
}

1530
/*
1531
 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1532 1533 1534 1535 1536 1537
 * is nothing.
 */
static void rcu_prepare_for_idle(int cpu)
{
}

1538 1539 1540 1541 1542 1543 1544 1545
/*
 * 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)
{
}

1546 1547
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */

1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562
/*
 * 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!
1563 1564 1565
 * 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.
1566 1567 1568 1569 1570
 *
 * 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.
 */
1571
#define RCU_IDLE_GP_DELAY 4		/* Roughly one grace period. */
1572
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ)	/* Roughly six seconds. */
1573

1574 1575 1576 1577
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);
1578

1579
extern int tick_nohz_active;
1580 1581

/*
1582 1583 1584
 * 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.
1585
 */
1586
static bool __maybe_unused rcu_try_advance_all_cbs(void)
1587
{
1588 1589
	bool cbs_ready = false;
	struct rcu_data *rdp;
1590
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1591 1592
	struct rcu_node *rnp;
	struct rcu_state *rsp;
1593

1594 1595
	/* Exit early if we advanced recently. */
	if (jiffies == rdtp->last_advance_all)
1596
		return false;
1597 1598
	rdtp->last_advance_all = jiffies;

1599 1600 1601
	for_each_rcu_flavor(rsp) {
		rdp = this_cpu_ptr(rsp->rda);
		rnp = rdp->mynode;
1602

1603 1604 1605 1606 1607 1608 1609
		/*
		 * 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 &&
		    rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
1610
			note_gp_changes(rsp, rdp);
1611

1612 1613 1614 1615
		if (cpu_has_callbacks_ready_to_invoke(rdp))
			cbs_ready = true;
	}
	return cbs_ready;
1616 1617
}

1618
/*
1619 1620 1621 1622
 * 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.
1623
 *
1624
 * The caller must have disabled interrupts.
1625
 */
1626
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1627
int rcu_needs_cpu(int cpu, unsigned long *dj)
1628 1629 1630
{
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);

1631 1632 1633
	/* Snapshot to detect later posting of non-lazy callback. */
	rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;

1634
	/* If no callbacks, RCU doesn't need the CPU. */
1635 1636
	if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
		*dj = ULONG_MAX;
1637 1638
		return 0;
	}
1639 1640 1641 1642 1643

	/* Attempt to advance callbacks. */
	if (rcu_try_advance_all_cbs()) {
		/* Some ready to invoke, so initiate later invocation. */
		invoke_rcu_core();
1644 1645
		return 1;
	}
1646 1647 1648
	rdtp->last_accelerate = jiffies;

	/* Request timer delay depending on laziness, and round. */
1649
	if (!rdtp->all_lazy) {
1650 1651
		*dj = round_up(rcu_idle_gp_delay + jiffies,
			       rcu_idle_gp_delay) - jiffies;
1652
	} else {
1653
		*dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1654
	}
1655 1656
	return 0;
}
1657
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1658

1659
/*
1660 1661 1662 1663 1664 1665
 * 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.
1666 1667
 *
 * The caller must have disabled interrupts.
1668
 */
1669
static void rcu_prepare_for_idle(int cpu)
1670
{
1671
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1672
	bool needwake;
1673
	struct rcu_data *rdp;
1674
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1675 1676
	struct rcu_node *rnp;
	struct rcu_state *rsp;
1677 1678 1679
	int tne;

	/* Handle nohz enablement switches conservatively. */
1680
	tne = ACCESS_ONCE(tick_nohz_active);
1681
	if (tne != rdtp->tick_nohz_enabled_snap) {
1682
		if (rcu_cpu_has_callbacks(cpu, NULL))
1683 1684 1685 1686 1687 1688
			invoke_rcu_core(); /* force nohz to see update. */
		rdtp->tick_nohz_enabled_snap = tne;
		return;
	}
	if (!tne)
		return;
1689

1690
	/* If this is a no-CBs CPU, no callbacks, just return. */
1691
	if (rcu_is_nocb_cpu(cpu))
1692 1693
		return;

1694
	/*
1695 1696 1697
	 * 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.
1698
	 */
1699 1700
	if (rdtp->all_lazy &&
	    rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1701 1702
		rdtp->all_lazy = false;
		rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1703
		invoke_rcu_core();
1704 1705 1706
		return;
	}

1707
	/*
1708 1709
	 * If we have not yet accelerated this jiffy, accelerate all
	 * callbacks on this CPU.
1710
	 */
1711
	if (rdtp->last_accelerate == jiffies)
1712
		return;
1713 1714 1715 1716 1717 1718 1719
	rdtp->last_accelerate = jiffies;
	for_each_rcu_flavor(rsp) {
		rdp = per_cpu_ptr(rsp->rda, cpu);
		if (!*rdp->nxttail[RCU_DONE_TAIL])
			continue;
		rnp = rdp->mynode;
		raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1720
		smp_mb__after_unlock_lock();
1721
		needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
1722
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1723 1724
		if (needwake)
			rcu_gp_kthread_wake(rsp);
1725
	}
1726
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1727
}
1728

1729 1730 1731 1732 1733 1734 1735
/*
 * 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(int cpu)
{
1736
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1737
	if (rcu_is_nocb_cpu(cpu))
1738
		return;
1739 1740
	if (rcu_try_advance_all_cbs())
		invoke_rcu_core();
1741
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1742 1743
}

1744
/*
1745 1746 1747 1748 1749 1750
 * 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().
1751 1752 1753
 */
static void rcu_idle_count_callbacks_posted(void)
{
1754
	__this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1755 1756
}

1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785
/*
 * 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) {
1786
		rdp = raw_cpu_ptr(rsp->rda);
1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807
		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);
1808
	smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1809 1810 1811 1812 1813 1814 1815 1816 1817 1818

	/*
	 * 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);
1819
		cond_resched_rcu_qs();
1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839
	}
	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);

1840
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1841 1842 1843 1844 1845 1846 1847

#ifdef CONFIG_RCU_CPU_STALL_INFO

#ifdef CONFIG_RCU_FAST_NO_HZ

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
1848
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1849
	unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1850

1851 1852 1853 1854 1855
	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');
1856 1857 1858 1859 1860 1861
}

#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
1862
	*cp = '\0';
1863 1864 1865 1866 1867 1868 1869
}

#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */

/* Initiate the stall-info list. */
static void print_cpu_stall_info_begin(void)
{
1870
	pr_cont("\n");
1871 1872 1873 1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900
}

/*
 * 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);
1901
	pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
1902 1903 1904
	       cpu, ticks_value, ticks_title,
	       atomic_read(&rdtp->dynticks) & 0xfff,
	       rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1905
	       rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1906 1907 1908 1909 1910 1911
	       fast_no_hz);
}

/* Terminate the stall-info list. */
static void print_cpu_stall_info_end(void)
{
1912
	pr_err("\t");
1913 1914 1915 1916 1917 1918
}

/* Zero ->ticks_this_gp for all flavors of RCU. */
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
	rdp->ticks_this_gp = 0;
1919
	rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1920 1921 1922 1923 1924
}

/* Increment ->ticks_this_gp for all flavors of RCU. */
static void increment_cpu_stall_ticks(void)
{
1925 1926 1927
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
1928
		raw_cpu_inc(rsp->rda->ticks_this_gp);
1929 1930 1931 1932 1933 1934
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

static void print_cpu_stall_info_begin(void)
{
1935
	pr_cont(" {");
1936 1937 1938 1939
}

static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
1940
	pr_cont(" %d", cpu);
1941 1942 1943 1944
}

static void print_cpu_stall_info_end(void)
{
1945
	pr_cont("} ");
1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956
}

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 */
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1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990

#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);

1991 1992 1993 1994 1995 1996 1997
static int __init parse_rcu_nocb_poll(char *arg)
{
	rcu_nocb_poll = 1;
	return 0;
}
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);

1998
/*
1999 2000
 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
 * grace period.
2001
 */
2002
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2003
{
2004
	wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
2005 2006 2007
}

/*
2008
 * Set the root rcu_node structure's ->need_future_gp field
2009 2010 2011 2012 2013
 * 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.
2014
 */
2015 2016
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
{
2017
	rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
2018 2019 2020
}

static void rcu_init_one_nocb(struct rcu_node *rnp)
2021
{
2022 2023
	init_waitqueue_head(&rnp->nocb_gp_wq[0]);
	init_waitqueue_head(&rnp->nocb_gp_wq[1]);
2024 2025
}

2026
#ifndef CONFIG_RCU_NOCB_CPU_ALL
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Liu Ping Fan 已提交
2027
/* Is the specified CPU a no-CBs CPU? */
2028
bool rcu_is_nocb_cpu(int cpu)
P
Paul E. McKenney 已提交
2029 2030 2031 2032 2033
{
	if (have_rcu_nocb_mask)
		return cpumask_test_cpu(cpu, rcu_nocb_mask);
	return false;
}
2034
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
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Paul E. McKenney 已提交
2035

2036 2037 2038 2039 2040 2041 2042 2043 2044
/*
 * 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;
2045
	if (ACCESS_ONCE(rdp_leader->nocb_leader_sleep) || force) {
2046
		/* Prior smp_mb__after_atomic() orders against prior enqueue. */
2047
		ACCESS_ONCE(rdp_leader->nocb_leader_sleep) = false;
2048 2049 2050 2051
		wake_up(&rdp_leader->nocb_wq);
	}
}

2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078
/*
 * 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);
	struct rcu_head *rhp;

	/* No-CBs CPUs might have callbacks on any of three lists. */
	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 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);
	}

	return !!rhp;
}

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Paul E. McKenney 已提交
2079 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089
/*
 * 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,
2090 2091
				    int rhcount, int rhcount_lazy,
				    unsigned long flags)
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Paul E. McKenney 已提交
2092 2093 2094 2095 2096 2097 2098 2099 2100 2101
{
	int len;
	struct rcu_head **old_rhpp;
	struct task_struct *t;

	/* Enqueue the callback on the nocb list and update counts. */
	old_rhpp = xchg(&rdp->nocb_tail, rhtp);
	ACCESS_ONCE(*old_rhpp) = rhp;
	atomic_long_add(rhcount, &rdp->nocb_q_count);
	atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
2102
	smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
P
Paul E. McKenney 已提交
2103 2104 2105

	/* If we are not being polled and there is a kthread, awaken it ... */
	t = ACCESS_ONCE(rdp->nocb_kthread);
2106
	if (rcu_nocb_poll || !t) {
2107 2108
		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
				    TPS("WakeNotPoll"));
P
Paul E. McKenney 已提交
2109
		return;
2110
	}
P
Paul E. McKenney 已提交
2111 2112
	len = atomic_long_read(&rdp->nocb_q_count);
	if (old_rhpp == &rdp->nocb_head) {
2113
		if (!irqs_disabled_flags(flags)) {
2114 2115
			/* ... if queue was empty ... */
			wake_nocb_leader(rdp, false);
2116 2117 2118
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    TPS("WakeEmpty"));
		} else {
2119
			rdp->nocb_defer_wakeup = RCU_NOGP_WAKE;
2120 2121 2122
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    TPS("WakeEmptyIsDeferred"));
		}
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Paul E. McKenney 已提交
2123 2124
		rdp->qlen_last_fqs_check = 0;
	} else if (len > rdp->qlen_last_fqs_check + qhimark) {
2125
		/* ... or if many callbacks queued. */
2126 2127 2128 2129 2130 2131 2132 2133 2134
		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"));
		}
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Paul E. McKenney 已提交
2135
		rdp->qlen_last_fqs_check = LONG_MAX / 2;
2136 2137
	} else {
		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
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Paul E. McKenney 已提交
2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148 2149 2150 2151
	}
	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,
2152
			    bool lazy, unsigned long flags)
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Paul E. McKenney 已提交
2153 2154
{

2155
	if (!rcu_is_nocb_cpu(rdp->cpu))
2156
		return false;
2157
	__call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
2158 2159 2160
	if (__is_kfree_rcu_offset((unsigned long)rhp->func))
		trace_rcu_kfree_callback(rdp->rsp->name, rhp,
					 (unsigned long)rhp->func,
2161 2162
					 -atomic_long_read(&rdp->nocb_q_count_lazy),
					 -atomic_long_read(&rdp->nocb_q_count));
2163 2164
	else
		trace_rcu_callback(rdp->rsp->name, rhp,
2165 2166
				   -atomic_long_read(&rdp->nocb_q_count_lazy),
				   -atomic_long_read(&rdp->nocb_q_count));
2167 2168 2169 2170 2171 2172 2173 2174 2175 2176 2177

	/*
	 * 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();

2178
	return true;
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Paul E. McKenney 已提交
2179 2180 2181 2182 2183 2184 2185
}

/*
 * 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,
2186 2187
						     struct rcu_data *rdp,
						     unsigned long flags)
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2188 2189 2190 2191 2192
{
	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. */
2193
	if (!rcu_is_nocb_cpu(smp_processor_id()))
2194
		return false;
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2195 2196 2197 2198 2199 2200
	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,
2201
					rsp->orphan_donetail, ql, qll, flags);
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		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,
2208
					rsp->orphan_nxttail, ql, qll, flags);
P
Paul E. McKenney 已提交
2209 2210 2211 2212
		ql = qll = 0;
		rsp->orphan_nxtlist = NULL;
		rsp->orphan_nxttail = &rsp->orphan_nxtlist;
	}
2213
	return true;
P
Paul E. McKenney 已提交
2214 2215 2216
}

/*
2217 2218
 * If necessary, kick off a new grace period, and either way wait
 * for a subsequent grace period to complete.
P
Paul E. McKenney 已提交
2219
 */
2220
static void rcu_nocb_wait_gp(struct rcu_data *rdp)
P
Paul E. McKenney 已提交
2221
{
2222
	unsigned long c;
2223
	bool d;
2224
	unsigned long flags;
2225
	bool needwake;
2226 2227 2228
	struct rcu_node *rnp = rdp->mynode;

	raw_spin_lock_irqsave(&rnp->lock, flags);
2229
	smp_mb__after_unlock_lock();
2230
	needwake = rcu_start_future_gp(rnp, rdp, &c);
2231
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
2232 2233
	if (needwake)
		rcu_gp_kthread_wake(rdp->rsp);
P
Paul E. McKenney 已提交
2234 2235

	/*
2236 2237
	 * Wait for the grace period.  Do so interruptibly to avoid messing
	 * up the load average.
P
Paul E. McKenney 已提交
2238
	 */
2239
	trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
2240
	for (;;) {
2241 2242 2243 2244
		wait_event_interruptible(
			rnp->nocb_gp_wq[c & 0x1],
			(d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
		if (likely(d))
2245
			break;
2246
		WARN_ON(signal_pending(current));
2247
		trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
2248
	}
2249
	trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
2250
	smp_mb(); /* Ensure that CB invocation happens after GP end. */
P
Paul E. McKenney 已提交
2251 2252
}

2253 2254 2255 2256 2257 2258 2259 2260 2261 2262 2263 2264 2265 2266 2267 2268 2269
/*
 * 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");
		wait_event_interruptible(my_rdp->nocb_wq,
2270
				!ACCESS_ONCE(my_rdp->nocb_leader_sleep));
2271 2272 2273 2274 2275 2276 2277 2278 2279 2280 2281 2282 2283 2284 2285 2286 2287 2288 2289 2290 2291 2292 2293 2294 2295 2296 2297 2298 2299 2300 2301 2302 2303 2304
		/* 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);
		rdp->nocb_gp_count = atomic_long_xchg(&rdp->nocb_q_count, 0);
		rdp->nocb_gp_count_lazy =
			atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
		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");
2305
		WARN_ON(signal_pending(current));
2306 2307 2308
		schedule_timeout_interruptible(1);

		/* Rescan in case we were a victim of memory ordering. */
2309 2310
		my_rdp->nocb_leader_sleep = true;
		smp_mb();  /* Ensure _sleep true before scan. */
2311 2312 2313
		for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower)
			if (ACCESS_ONCE(rdp->nocb_head)) {
				/* Found CB, so short-circuit next wait. */
2314
				my_rdp->nocb_leader_sleep = false;
2315 2316 2317 2318 2319 2320 2321 2322 2323
				break;
			}
		goto wait_again;
	}

	/* Wait for one grace period. */
	rcu_nocb_wait_gp(my_rdp);

	/*
2324 2325
	 * We left ->nocb_leader_sleep unset to reduce cache thrashing.
	 * We set it now, but recheck for new callbacks while
2326 2327
	 * traversing our follower list.
	 */
2328 2329
	my_rdp->nocb_leader_sleep = true;
	smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */
2330 2331 2332 2333

	/* 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))
2334
			my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
2335 2336 2337 2338 2339 2340 2341 2342 2343
		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;
		atomic_long_add(rdp->nocb_gp_count, &rdp->nocb_follower_count);
		atomic_long_add(rdp->nocb_gp_count_lazy,
				&rdp->nocb_follower_count_lazy);
2344
		smp_mb__after_atomic(); /* Store *tail before wakeup. */
2345 2346 2347 2348 2349 2350 2351 2352 2353 2354 2355 2356 2357 2358 2359 2360 2361 2362 2363 2364 2365 2366 2367 2368 2369 2370 2371 2372 2373 2374 2375 2376 2377 2378 2379 2380 2381 2382 2383 2384
		if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
			/*
			 * List was empty, wake up the follower.
			 * Memory barriers supplied by atomic_long_add().
			 */
			wake_up(&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");
			wait_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");
2385
		WARN_ON(signal_pending(current));
2386 2387 2388 2389
		schedule_timeout_interruptible(1);
	}
}

P
Paul E. McKenney 已提交
2390 2391
/*
 * Per-rcu_data kthread, but only for no-CBs CPUs.  Each kthread invokes
2392 2393 2394
 * 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.
P
Paul E. McKenney 已提交
2395 2396 2397 2398 2399 2400 2401 2402 2403 2404 2405
 */
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 (;;) {
2406 2407 2408 2409 2410 2411 2412 2413 2414 2415 2416 2417 2418 2419 2420 2421
		/* 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);
		c = atomic_long_xchg(&rdp->nocb_follower_count, 0);
		cl = atomic_long_xchg(&rdp->nocb_follower_count_lazy, 0);
		rdp->nocb_p_count += c;
		rdp->nocb_p_count_lazy += cl;
P
Paul E. McKenney 已提交
2422 2423 2424 2425 2426 2427 2428 2429

		/* Each pass through the following loop invokes a callback. */
		trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
		c = cl = 0;
		while (list) {
			next = list->next;
			/* Wait for enqueuing to complete, if needed. */
			while (next == NULL && &list->next != tail) {
2430 2431
				trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
						    TPS("WaitQueue"));
P
Paul E. McKenney 已提交
2432
				schedule_timeout_interruptible(1);
2433 2434
				trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
						    TPS("WokeQueue"));
P
Paul E. McKenney 已提交
2435 2436 2437 2438 2439 2440 2441 2442 2443 2444 2445
				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);
2446 2447 2448
		ACCESS_ONCE(rdp->nocb_p_count) = rdp->nocb_p_count - c;
		ACCESS_ONCE(rdp->nocb_p_count_lazy) =
						rdp->nocb_p_count_lazy - cl;
2449
		rdp->n_nocbs_invoked += c;
P
Paul E. McKenney 已提交
2450 2451 2452 2453
	}
	return 0;
}

2454
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
2455
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2456 2457 2458 2459 2460 2461 2462
{
	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)
{
2463 2464
	int ndw;

2465 2466
	if (!rcu_nocb_need_deferred_wakeup(rdp))
		return;
2467 2468 2469 2470
	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"));
2471 2472
}

2473 2474 2475 2476 2477 2478 2479 2480 2481 2482 2483 2484 2485 2486 2487 2488
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) {
2489 2490 2491 2492
		if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
			pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
			return;
		}
2493 2494 2495 2496 2497 2498 2499 2500 2501 2502 2503 2504 2505 2506 2507 2508 2509 2510 2511 2512 2513 2514 2515 2516 2517 2518 2519 2520 2521 2522 2523 2524 2525 2526 2527 2528 2529 2530 2531 2532 2533
		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);
	}
	cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
	pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
	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) {
			struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);

			/*
			 * If there are early callbacks, they will need
			 * to be moved to the nocb lists.
			 */
			WARN_ON_ONCE(rdp->nxttail[RCU_NEXT_TAIL] !=
				     &rdp->nxtlist &&
				     rdp->nxttail[RCU_NEXT_TAIL] != NULL);
			init_nocb_callback_list(rdp);
		}
2534
		rcu_organize_nocb_kthreads(rsp);
2535
	}
2536 2537
}

P
Paul E. McKenney 已提交
2538 2539 2540 2541 2542
/* 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_waitqueue_head(&rdp->nocb_wq);
2543
	rdp->nocb_follower_tail = &rdp->nocb_follower_head;
P
Paul E. McKenney 已提交
2544 2545
}

2546 2547 2548 2549 2550 2551 2552 2553 2554 2555 2556 2557 2558 2559 2560 2561 2562 2563 2564 2565 2566 2567 2568 2569 2570 2571 2572 2573 2574 2575 2576 2577 2578 2579 2580 2581 2582 2583 2584 2585 2586 2587 2588 2589 2590 2591 2592 2593 2594 2595 2596 2597 2598 2599 2600 2601 2602 2603 2604 2605 2606 2607 2608 2609 2610 2611 2612 2613 2614 2615 2616
/*
 * 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;
			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);
}

2617 2618 2619 2620 2621
/* 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);

/*
2622
 * Initialize leader-follower relationships for all no-CBs CPU.
2623
 */
2624
static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
P
Paul E. McKenney 已提交
2625 2626
{
	int cpu;
2627 2628
	int ls = rcu_nocb_leader_stride;
	int nl = 0;  /* Next leader. */
P
Paul E. McKenney 已提交
2629
	struct rcu_data *rdp;
2630 2631
	struct rcu_data *rdp_leader = NULL;  /* Suppress misguided gcc warn. */
	struct rcu_data *rdp_prev = NULL;
P
Paul E. McKenney 已提交
2632

2633
	if (!have_rcu_nocb_mask)
P
Paul E. McKenney 已提交
2634
		return;
2635 2636 2637 2638 2639 2640 2641 2642 2643
	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().
	 */
P
Paul E. McKenney 已提交
2644 2645
	for_each_cpu(cpu, rcu_nocb_mask) {
		rdp = per_cpu_ptr(rsp->rda, cpu);
2646 2647 2648 2649 2650 2651 2652 2653 2654 2655 2656
		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;
P
Paul E. McKenney 已提交
2657 2658 2659 2660
	}
}

/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2661
static bool init_nocb_callback_list(struct rcu_data *rdp)
P
Paul E. McKenney 已提交
2662
{
2663
	if (!rcu_is_nocb_cpu(rdp->cpu))
2664
		return false;
2665

P
Paul E. McKenney 已提交
2666
	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2667
	return true;
P
Paul E. McKenney 已提交
2668 2669
}

2670 2671
#else /* #ifdef CONFIG_RCU_NOCB_CPU */

2672 2673 2674 2675 2676 2677
static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
{
	WARN_ON_ONCE(1); /* Should be dead code. */
	return false;
}

2678
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
P
Paul E. McKenney 已提交
2679 2680 2681
{
}

2682 2683 2684 2685 2686 2687 2688
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
{
}

static void rcu_init_one_nocb(struct rcu_node *rnp)
{
}
P
Paul E. McKenney 已提交
2689 2690

static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2691
			    bool lazy, unsigned long flags)
P
Paul E. McKenney 已提交
2692
{
2693
	return false;
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2694 2695 2696
}

static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2697 2698
						     struct rcu_data *rdp,
						     unsigned long flags)
P
Paul E. McKenney 已提交
2699
{
2700
	return false;
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2701 2702 2703 2704 2705 2706
}

static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
{
}

2707
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2708 2709 2710 2711 2712 2713 2714 2715
{
	return false;
}

static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
{
}

2716 2717 2718 2719 2720
static void rcu_spawn_all_nocb_kthreads(int cpu)
{
}

static void __init rcu_spawn_nocb_kthreads(void)
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Paul E. McKenney 已提交
2721 2722 2723
{
}

2724
static bool init_nocb_callback_list(struct rcu_data *rdp)
P
Paul E. McKenney 已提交
2725
{
2726
	return false;
P
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2727 2728 2729
}

#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2730 2731 2732 2733 2734 2735 2736 2737 2738 2739

/*
 * 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.
 */
2740
static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
2741 2742 2743 2744 2745 2746
{
#ifdef CONFIG_NO_HZ_FULL
	if (tick_nohz_full_cpu(cpu))
		smp_send_reschedule(cpu);
#endif /* #ifdef CONFIG_NO_HZ_FULL */
}
2747 2748 2749 2750


#ifdef CONFIG_NO_HZ_FULL_SYSIDLE

2751
static int full_sysidle_state;		/* Current system-idle state. */
2752 2753 2754 2755 2756 2757
#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. */

2758 2759 2760 2761 2762 2763
/*
 * 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.
 */
2764
static void rcu_sysidle_enter(int irq)
2765 2766
{
	unsigned long j;
2767
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
2768

2769 2770 2771 2772
	/* If there are no nohz_full= CPUs, no need to track this. */
	if (!tick_nohz_full_enabled())
		return;

2773 2774 2775 2776 2777 2778 2779 2780 2781 2782 2783 2784 2785 2786 2787 2788 2789 2790 2791 2792
	/* 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;
2793
	smp_mb__before_atomic();
2794
	atomic_inc(&rdtp->dynticks_idle);
2795
	smp_mb__after_atomic();
2796 2797 2798
	WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
}

2799 2800 2801 2802 2803 2804 2805 2806 2807 2808 2809 2810 2811 2812 2813 2814 2815 2816 2817 2818 2819 2820 2821 2822 2823 2824 2825 2826 2827 2828 2829 2830
/*
 * 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. */
}

2831 2832 2833 2834 2835
/*
 * 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.
 */
2836
static void rcu_sysidle_exit(int irq)
2837
{
2838 2839
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

2840 2841 2842 2843
	/* If there are no nohz_full= CPUs, no need to track this. */
	if (!tick_nohz_full_enabled())
		return;

2844 2845 2846 2847 2848 2849 2850 2851 2852 2853 2854 2855 2856 2857 2858 2859 2860 2861 2862 2863 2864 2865
	/* 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. */
2866
	smp_mb__before_atomic();
2867
	atomic_inc(&rdtp->dynticks_idle);
2868
	smp_mb__after_atomic();
2869
	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
2870 2871 2872 2873 2874 2875 2876 2877 2878 2879 2880 2881 2882 2883 2884 2885 2886 2887 2888 2889 2890 2891 2892 2893 2894 2895 2896 2897

	/*
	 * 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.
 */
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;

2898 2899 2900 2901
	/* If there are no nohz_full= CPUs, don't check system-wide idleness. */
	if (!tick_nohz_full_enabled())
		return;

2902 2903 2904 2905 2906
	/*
	 * 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.
	 */
2907
	if (!*isidle || rdp->rsp != rcu_state_p ||
2908 2909
	    cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
		return;
2910 2911
	if (rcu_gp_in_progress(rdp->rsp))
		WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
2912 2913 2914 2915 2916 2917 2918 2919 2920 2921 2922 2923 2924 2925 2926 2927 2928 2929 2930 2931 2932

	/* 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)
{
2933
	return rsp == rcu_state_p;
2934 2935 2936 2937 2938 2939 2940 2941 2942 2943 2944 2945 2946 2947 2948 2949 2950 2951 2952 2953 2954 2955 2956 2957 2958 2959 2960 2961 2962 2963 2964 2965 2966 2967 2968 2969 2970 2971 2972 2973 2974 2975 2976 2977 2978 2979 2980 2981 2982 2983 2984 2985 2986 2987 2988 2989 2990 2991 2992 2993 2994 2995 2996 2997 2998 2999
}

/*
 * 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();
3000 3001
	if (full_sysidle_state > RCU_SYSIDLE_SHORT)
		ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
3002 3003 3004 3005 3006 3007 3008 3009 3010
}

/*
 * 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)
{
3011
	if (rsp != rcu_state_p)
3012 3013 3014 3015 3016 3017 3018 3019 3020 3021 3022 3023 3024 3025 3026 3027
		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)
{
3028 3029 3030 3031
	/* If there are no nohz_full= CPUs, no need to track this. */
	if (!tick_nohz_full_enabled())
		return;

3032 3033 3034 3035 3036 3037 3038 3039 3040 3041 3042 3043 3044 3045 3046 3047 3048 3049 3050 3051 3052 3053 3054 3055 3056 3057
	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.
3058 3059
 * The caller must have disabled interrupts.  This is not intended to be
 * called unless tick_nohz_full_enabled().
3060 3061 3062 3063 3064 3065 3066 3067 3068 3069 3070 3071 3072 3073 3074 3075 3076 3077 3078 3079 3080 3081 3082 3083 3084
 */
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) {
3085
				rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
3086 3087 3088 3089
				rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
				if (!isidle)
					break;
			}
3090
			rcu_sysidle_report(rcu_state_p, isidle, maxj, false);
3091 3092 3093 3094 3095 3096 3097 3098 3099 3100 3101 3102 3103 3104 3105 3106 3107 3108 3109 3110 3111 3112 3113 3114 3115 3116
			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 &&
3117
	    !rcu_gp_in_progress(rcu_state_p) &&
3118 3119 3120
	    !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
		call_rcu(&rsh.rh, rcu_sysidle_cb);
	return false;
3121 3122
}

3123 3124 3125 3126 3127 3128 3129 3130 3131 3132
/*
 * 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 */

3133
static void rcu_sysidle_enter(int irq)
3134 3135 3136
{
}

3137
static void rcu_sysidle_exit(int irq)
3138 3139 3140
{
}

3141 3142 3143 3144 3145 3146 3147 3148 3149 3150 3151 3152 3153 3154 3155
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)
{
}

3156 3157 3158 3159 3160
static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
{
}

#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3161 3162 3163 3164 3165 3166 3167 3168

/*
 * 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
3169
 * CONFIG_RCU_NOCB_CPU CPUs.
3170 3171 3172 3173 3174 3175 3176 3177 3178 3179 3180
 */
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;
}
3181 3182 3183 3184 3185 3186 3187

/*
 * Bind the grace-period kthread for the sysidle flavor of RCU to the
 * timekeeping CPU.
 */
static void rcu_bind_gp_kthread(void)
{
3188
	int __maybe_unused cpu;
3189

3190
	if (!tick_nohz_full_enabled())
3191
		return;
3192 3193 3194
#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
	cpu = tick_do_timer_cpu;
	if (cpu >= 0 && cpu < nr_cpu_ids && raw_smp_processor_id() != cpu)
3195
		set_cpus_allowed_ptr(current, cpumask_of(cpu));
3196 3197 3198 3199
#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
	if (!is_housekeeping_cpu(raw_smp_processor_id()))
		housekeeping_affine(current);
#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3200
}
3201 3202 3203 3204 3205 3206 3207 3208 3209 3210 3211 3212 3213 3214 3215 3216

/* 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) */
}