tree_plugin.h 83.0 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
#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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#ifdef CONFIG_RCU_NOCB_CPU
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#ifndef CONFIG_RCU_NOCB_CPU_NONE
	if (!have_rcu_nocb_mask) {
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		zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
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		have_rcu_nocb_mask = true;
	}
#ifdef CONFIG_RCU_NOCB_CPU_ZERO
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	pr_info("\tOffload RCU callbacks from CPU 0\n");
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	cpumask_set_cpu(0, rcu_nocb_mask);
#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
#ifdef CONFIG_RCU_NOCB_CPU_ALL
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	pr_info("\tOffload RCU callbacks from all CPUs\n");
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	cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
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#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
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	if (have_rcu_nocb_mask) {
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		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);
		}
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		cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
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		pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
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		if (rcu_nocb_poll)
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			pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
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	}
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
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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.
 */
long rcu_batches_completed_preempt(void)
{
	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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 *
 * Unlike the other rcu_*_qs() functions, callers to this function
 * must disable irqs in order to protect the assignment to
 * ->rcu_read_unlock_special.
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 */
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static void rcu_preempt_qs(int cpu)
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{
	struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
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	if (rdp->passed_quiesce == 0)
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		trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
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	rdp->passed_quiesce = 1;
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	current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
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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 & RCU_READ_UNLOCK_BLOCKED) == 0) {

		/* 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 |= RCU_READ_UNLOCK_BLOCKED;
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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 &&
		   t->rcu_read_unlock_special) {

		/*
		 * 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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	local_irq_save(flags);
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	rcu_preempt_qs(cpu);
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	local_irq_restore(flags);
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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
	struct rt_mutex *rbmp = NULL;
#endif /* #ifdef CONFIG_RCU_BOOST */
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	struct rcu_node *rnp;
	int special;

	/* NMI handlers cannot block and cannot safely manipulate state. */
	if (in_nmi())
		return;

	local_irq_save(flags);

	/*
	 * If RCU core is waiting for this CPU to exit critical section,
	 * let it know that we have done so.
	 */
	special = t->rcu_read_unlock_special;
	if (special & RCU_READ_UNLOCK_NEED_QS) {
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		rcu_preempt_qs(smp_processor_id());
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		if (!t->rcu_read_unlock_special) {
			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. */
	if (special & RCU_READ_UNLOCK_BLOCKED) {
		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;

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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/clear ->rcu_boost_mutex with rcu_node lock held. */
		if (t->rcu_boost_mutex) {
			rbmp = t->rcu_boost_mutex;
			t->rcu_boost_mutex = NULL;
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		}
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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 (rbmp)
			rt_mutex_unlock(rbmp);
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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));
549 550
	if (!list_empty(&rnp->blkd_tasks))
		rnp->gp_tasks = rnp->blkd_tasks.next;
551
	WARN_ON_ONCE(rnp->qsmask);
552 553
}

554 555
#ifdef CONFIG_HOTPLUG_CPU

556 557 558 559 560 561
/*
 * 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.
562 563
 * Returns true if there were tasks blocking the current RCU grace
 * period.
564
 *
565 566 567
 * Returns 1 if there was previously a task blocking the current grace
 * period on the specified rcu_node structure.
 *
568 569
 * The caller must hold rnp->lock with irqs disabled.
 */
570 571 572
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
				     struct rcu_node *rnp,
				     struct rcu_data *rdp)
573 574 575
{
	struct list_head *lp;
	struct list_head *lp_root;
576
	int retval = 0;
577
	struct rcu_node *rnp_root = rcu_get_root(rsp);
578
	struct task_struct *t;
579

580 581
	if (rnp == rnp_root) {
		WARN_ONCE(1, "Last CPU thought to be offlined?");
582
		return 0;  /* Shouldn't happen: at least one CPU online. */
583
	}
584 585 586

	/* If we are on an internal node, complain bitterly. */
	WARN_ON_ONCE(rnp != rdp->mynode);
587 588

	/*
589 590 591 592 593 594 595
	 * 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.
596
	 */
597
	if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
598 599 600
		retval |= RCU_OFL_TASKS_NORM_GP;
	if (rcu_preempted_readers_exp(rnp))
		retval |= RCU_OFL_TASKS_EXP_GP;
601 602 603 604 605
	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 */
606
		smp_mb__after_unlock_lock();
607 608 609 610 611 612 613
		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;
614 615 616 617
#ifdef CONFIG_RCU_BOOST
		if (&t->rcu_node_entry == rnp->boost_tasks)
			rnp_root->boost_tasks = rnp->boost_tasks;
#endif /* #ifdef CONFIG_RCU_BOOST */
618
		raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
619
	}
620

621 622
	rnp->gp_tasks = NULL;
	rnp->exp_tasks = NULL;
623
#ifdef CONFIG_RCU_BOOST
624
	rnp->boost_tasks = NULL;
625 626 627 628 629
	/*
	 * 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.
	 */
630
	raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
631
	smp_mb__after_unlock_lock();
632
	if (rnp_root->boost_tasks != NULL &&
633 634
	    rnp_root->boost_tasks != rnp_root->gp_tasks &&
	    rnp_root->boost_tasks != rnp_root->exp_tasks)
635 636 637 638
		rnp_root->boost_tasks = rnp_root->gp_tasks;
	raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
#endif /* #ifdef CONFIG_RCU_BOOST */

639
	return retval;
640 641
}

642 643
#endif /* #ifdef CONFIG_HOTPLUG_CPU */

644 645 646 647 648 649 650 651 652 653 654 655
/*
 * Check for a quiescent state from the current CPU.  When a task blocks,
 * the task is recorded in the corresponding CPU's rcu_node structure,
 * which is checked elsewhere.
 *
 * Caller must disable hard irqs.
 */
static void rcu_preempt_check_callbacks(int cpu)
{
	struct task_struct *t = current;

	if (t->rcu_read_lock_nesting == 0) {
656
		rcu_preempt_qs(cpu);
657 658
		return;
	}
659 660
	if (t->rcu_read_lock_nesting > 0 &&
	    per_cpu(rcu_preempt_data, cpu).qs_pending)
661
		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
662 663
}

664 665
#ifdef CONFIG_RCU_BOOST

666 667
static void rcu_preempt_do_callbacks(void)
{
668
	rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
669 670
}

671 672
#endif /* #ifdef CONFIG_RCU_BOOST */

673
/*
P
Paul E. McKenney 已提交
674
 * Queue a preemptible-RCU callback for invocation after a grace period.
675 676 677
 */
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
P
Paul E. McKenney 已提交
678
	__call_rcu(head, func, &rcu_preempt_state, -1, 0);
679 680 681
}
EXPORT_SYMBOL_GPL(call_rcu);

682 683 684 685 686
/**
 * 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
687 688 689 690 691
 * 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.
692 693 694
 *
 * See the description of synchronize_sched() for more detailed information
 * on memory ordering guarantees.
695 696 697
 */
void synchronize_rcu(void)
{
698 699 700 701
	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");
702 703
	if (!rcu_scheduler_active)
		return;
704 705 706 707
	if (rcu_expedited)
		synchronize_rcu_expedited();
	else
		wait_rcu_gp(call_rcu);
708 709 710
}
EXPORT_SYMBOL_GPL(synchronize_rcu);

711
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
712
static unsigned long sync_rcu_preempt_exp_count;
713 714 715 716 717 718 719 720 721 722
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)
{
723
	return rnp->exp_tasks != NULL;
724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748
}

/*
 * 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!)
 *
749 750 751
 * Most callers will set the "wake" flag, but the task initiating the
 * expedited grace period need not wake itself.
 *
752 753
 * Caller must hold sync_rcu_preempt_exp_mutex.
 */
754 755
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
			       bool wake)
756 757 758 759
{
	unsigned long flags;
	unsigned long mask;

P
Paul E. McKenney 已提交
760
	raw_spin_lock_irqsave(&rnp->lock, flags);
761
	smp_mb__after_unlock_lock();
762
	for (;;) {
763 764
		if (!sync_rcu_preempt_exp_done(rnp)) {
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
765
			break;
766
		}
767
		if (rnp->parent == NULL) {
768
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
769 770
			if (wake) {
				smp_mb(); /* EGP done before wake_up(). */
771
				wake_up(&sync_rcu_preempt_exp_wq);
772
			}
773 774 775
			break;
		}
		mask = rnp->grpmask;
P
Paul E. McKenney 已提交
776
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
777
		rnp = rnp->parent;
P
Paul E. McKenney 已提交
778
		raw_spin_lock(&rnp->lock); /* irqs already disabled */
779
		smp_mb__after_unlock_lock();
780 781 782 783 784 785 786 787 788
		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.
 *
789 790
 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
 * CPU hotplug operations.
791 792 793 794
 */
static void
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
{
795
	unsigned long flags;
796
	int must_wait = 0;
797

798
	raw_spin_lock_irqsave(&rnp->lock, flags);
799
	smp_mb__after_unlock_lock();
800
	if (list_empty(&rnp->blkd_tasks)) {
801
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
802
	} else {
803
		rnp->exp_tasks = rnp->blkd_tasks.next;
804
		rcu_initiate_boost(rnp, flags);  /* releases rnp->lock */
805 806
		must_wait = 1;
	}
807
	if (!must_wait)
808
		rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
809 810
}

811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826
/**
 * 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.
 *
 * Note that it is illegal to call this function while holding any lock
 * that is acquired by a CPU-hotplug notifier.  And yes, it is also illegal
 * to call this function from a CPU-hotplug notifier.  Failing to observe
 * these restriction will result in deadlock.
827 828 829
 */
void synchronize_rcu_expedited(void)
{
830 831 832
	unsigned long flags;
	struct rcu_node *rnp;
	struct rcu_state *rsp = &rcu_preempt_state;
833
	unsigned long snap;
834 835 836 837 838 839
	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. */

840 841 842 843 844 845 846 847 848 849
	/*
	 * 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.
	 */
	get_online_cpus();

850 851 852 853 854 855
	/*
	 * 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)) {
856 857 858 859 860
		if (ULONG_CMP_LT(snap,
		    ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
			put_online_cpus();
			goto mb_ret; /* Others did our work for us. */
		}
861
		if (trycount++ < 10) {
862
			udelay(trycount * num_online_cpus());
863
		} else {
864
			put_online_cpus();
865
			wait_rcu_gp(call_rcu);
866 867 868
			return;
		}
	}
869 870
	if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
		put_online_cpus();
871
		goto unlock_mb_ret; /* Others did our work for us. */
872
	}
873

874
	/* force all RCU readers onto ->blkd_tasks lists. */
875 876 877 878
	synchronize_sched_expedited();

	/* Initialize ->expmask for all non-leaf rcu_node structures. */
	rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
879
		raw_spin_lock_irqsave(&rnp->lock, flags);
880
		smp_mb__after_unlock_lock();
881
		rnp->expmask = rnp->qsmaskinit;
882
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
883 884
	}

885
	/* Snapshot current state of ->blkd_tasks lists. */
886 887 888 889 890
	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));

891
	put_online_cpus();
892

893
	/* Wait for snapshotted ->blkd_tasks lists to drain. */
894 895 896 897 898 899 900 901 902 903 904
	rnp = rcu_get_root(rsp);
	wait_event(sync_rcu_preempt_exp_wq,
		   sync_rcu_preempt_exp_done(rnp));

	/* Clean up and exit. */
	smp_mb(); /* ensure expedited GP seen before counter increment. */
	ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
unlock_mb_ret:
	mutex_unlock(&sync_rcu_preempt_exp_mutex);
mb_ret:
	smp_mb(); /* ensure subsequent action seen after grace period. */
905 906 907
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

908 909
/**
 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
910 911 912 913 914
 *
 * 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.
915 916 917
 */
void rcu_barrier(void)
{
918
	_rcu_barrier(&rcu_preempt_state);
919 920 921
}
EXPORT_SYMBOL_GPL(rcu_barrier);

922
/*
P
Paul E. McKenney 已提交
923
 * Initialize preemptible RCU's state structures.
924 925 926
 */
static void __init __rcu_init_preempt(void)
{
927
	rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
928 929
}

930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947
/*
 * 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();
	t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
	__rcu_read_unlock();
}

948 949
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */

950
static struct rcu_state *rcu_state_p = &rcu_sched_state;
951

952 953 954
/*
 * Tell them what RCU they are running.
 */
955
static void __init rcu_bootup_announce(void)
956
{
957
	pr_info("Hierarchical RCU implementation.\n");
958
	rcu_bootup_announce_oddness();
959 960 961 962 963 964 965 966 967 968 969
}

/*
 * 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);

970 971 972 973 974 975 976 977
/*
 * 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)
{
}

978
/*
P
Paul E. McKenney 已提交
979
 * Because preemptible RCU does not exist, there are never any preempted
980 981
 * RCU readers.
 */
982
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
983 984 985 986
{
	return 0;
}

987 988 989
#ifdef CONFIG_HOTPLUG_CPU

/* Because preemptible RCU does not exist, no quieting of tasks. */
P
Paul E. McKenney 已提交
990
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
991
{
P
Paul E. McKenney 已提交
992
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
993 994 995 996
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

997
/*
P
Paul E. McKenney 已提交
998
 * Because preemptible RCU does not exist, we never have to check for
999 1000 1001 1002 1003 1004
 * tasks blocked within RCU read-side critical sections.
 */
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}

1005
/*
P
Paul E. McKenney 已提交
1006
 * Because preemptible RCU does not exist, we never have to check for
1007 1008
 * tasks blocked within RCU read-side critical sections.
 */
1009
static int rcu_print_task_stall(struct rcu_node *rnp)
1010
{
1011
	return 0;
1012 1013
}

1014
/*
P
Paul E. McKenney 已提交
1015
 * Because there is no preemptible RCU, there can be no readers blocked,
1016 1017
 * so there is no need to check for blocked tasks.  So check only for
 * bogus qsmask values.
1018 1019 1020
 */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
1021
	WARN_ON_ONCE(rnp->qsmask);
1022 1023
}

1024 1025
#ifdef CONFIG_HOTPLUG_CPU

1026
/*
P
Paul E. McKenney 已提交
1027
 * Because preemptible RCU does not exist, it never needs to migrate
1028 1029 1030
 * tasks that were blocked within RCU read-side critical sections, and
 * such non-existent tasks cannot possibly have been blocking the current
 * grace period.
1031
 */
1032 1033 1034
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
				     struct rcu_node *rnp,
				     struct rcu_data *rdp)
1035
{
1036
	return 0;
1037 1038
}

1039 1040
#endif /* #ifdef CONFIG_HOTPLUG_CPU */

1041
/*
P
Paul E. McKenney 已提交
1042
 * Because preemptible RCU does not exist, it never has any callbacks
1043 1044
 * to check.
 */
1045
static void rcu_preempt_check_callbacks(int cpu)
1046 1047 1048
{
}

1049 1050
/*
 * Wait for an rcu-preempt grace period, but make it happen quickly.
P
Paul E. McKenney 已提交
1051
 * But because preemptible RCU does not exist, map to rcu-sched.
1052 1053 1054 1055 1056 1057 1058
 */
void synchronize_rcu_expedited(void)
{
	synchronize_sched_expedited();
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

1059 1060 1061
#ifdef CONFIG_HOTPLUG_CPU

/*
P
Paul E. McKenney 已提交
1062
 * Because preemptible RCU does not exist, there is never any need to
1063 1064 1065
 * report on tasks preempted in RCU read-side critical sections during
 * expedited RCU grace periods.
 */
1066 1067
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
			       bool wake)
1068 1069 1070 1071 1072
{
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

1073
/*
P
Paul E. McKenney 已提交
1074
 * Because preemptible RCU does not exist, rcu_barrier() is just
1075 1076 1077 1078 1079 1080 1081 1082
 * another name for rcu_barrier_sched().
 */
void rcu_barrier(void)
{
	rcu_barrier_sched();
}
EXPORT_SYMBOL_GPL(rcu_barrier);

1083
/*
P
Paul E. McKenney 已提交
1084
 * Because preemptible RCU does not exist, it need not be initialized.
1085 1086 1087 1088 1089
 */
static void __init __rcu_init_preempt(void)
{
}

1090 1091 1092 1093 1094 1095 1096 1097
/*
 * Because preemptible RCU does not exist, tasks cannot possibly exit
 * while in preemptible RCU read-side critical sections.
 */
void exit_rcu(void)
{
}

1098
#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1099

1100 1101
#ifdef CONFIG_RCU_BOOST

1102
#include "../locking/rtmutex_common.h"
1103

1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116
#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 &&
1117
		 ULONG_CMP_LT(jiffies, rnp->boost_time))
1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130
		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 */

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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);
}

1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159
/*
 * 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 rt_mutex mtx;
	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);
1160
	smp_mb__after_unlock_lock();
1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176

	/*
	 * 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.
	 */
1177
	if (rnp->exp_tasks != NULL) {
1178
		tb = rnp->exp_tasks;
1179 1180
		rnp->n_exp_boosts++;
	} else {
1181
		tb = rnp->boost_tasks;
1182 1183 1184
		rnp->n_normal_boosts++;
	}
	rnp->n_tasks_boosted++;
1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208

	/*
	 * We boost task t by manufacturing an rt_mutex that appears to
	 * be held by task t.  We leave a pointer to that rt_mutex where
	 * task t can find it, and task t will release the mutex when it
	 * exits its outermost RCU read-side critical section.  Then
	 * simply acquiring this artificial rt_mutex will boost task
	 * t's priority.  (Thanks to tglx for suggesting this approach!)
	 *
	 * Note that task t must acquire rnp->lock to remove itself from
	 * the ->blkd_tasks list, which it will do from exit() if from
	 * nowhere else.  We therefore are guaranteed that task t will
	 * stay around at least until we drop rnp->lock.  Note that
	 * rnp->lock also resolves races between our priority boosting
	 * and task t's exiting its outermost RCU read-side critical
	 * section.
	 */
	t = container_of(tb, struct task_struct, rcu_node_entry);
	rt_mutex_init_proxy_locked(&mtx, t);
	t->rcu_boost_mutex = &mtx;
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
	rt_mutex_lock(&mtx);  /* Side effect: boosts task t's priority. */
	rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */

1209 1210
	return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
	       ACCESS_ONCE(rnp->boost_tasks) != NULL;
1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222
}

/*
 * 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;

1223
	trace_rcu_utilization(TPS("Start boost kthread@init"));
1224
	for (;;) {
1225
		rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1226
		trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1227
		rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1228
		trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1229
		rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1230 1231 1232 1233 1234 1235
		more2boost = rcu_boost(rnp);
		if (more2boost)
			spincnt++;
		else
			spincnt = 0;
		if (spincnt > 10) {
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			rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1237
			trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
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			schedule_timeout_interruptible(2);
1239
			trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1240 1241 1242
			spincnt = 0;
		}
	}
1243
	/* NOTREACHED */
1244
	trace_rcu_utilization(TPS("End boost kthread@notreached"));
1245 1246 1247 1248 1249 1250 1251 1252 1253
	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.
 *
1254 1255 1256
 * 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.
1257
 */
1258
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1259 1260 1261
{
	struct task_struct *t;

1262 1263
	if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
		rnp->n_balk_exp_gp_tasks++;
1264
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1265
		return;
1266
	}
1267 1268 1269 1270 1271 1272 1273
	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;
1274
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1275
		t = rnp->boost_kthread_task;
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1276 1277
		if (t)
			rcu_wake_cond(t, rnp->boost_kthread_status);
1278
	} else {
1279
		rcu_initiate_boost_trace(rnp);
1280 1281
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
	}
1282 1283
}

1284 1285 1286 1287 1288 1289 1290 1291 1292
/*
 * 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);
1293
	if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
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1294 1295 1296 1297
	    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));
	}
1298 1299 1300
	local_irq_restore(flags);
}

1301 1302 1303 1304 1305 1306
/*
 * Is the current CPU running the RCU-callbacks kthread?
 * Caller must have preemption disabled.
 */
static bool rcu_is_callbacks_kthread(void)
{
1307
	return __this_cpu_read(rcu_cpu_kthread_task) == current;
1308 1309
}

1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324
#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.
 */
1325
static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
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						 struct rcu_node *rnp)
1327
{
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	int rnp_index = rnp - &rsp->node[0];
1329 1330 1331 1332 1333 1334
	unsigned long flags;
	struct sched_param sp;
	struct task_struct *t;

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

1339
	rsp->boost = 1;
1340 1341 1342
	if (rnp->boost_kthread_task != NULL)
		return 0;
	t = kthread_create(rcu_boost_kthread, (void *)rnp,
1343
			   "rcub/%d", rnp_index);
1344 1345 1346
	if (IS_ERR(t))
		return PTR_ERR(t);
	raw_spin_lock_irqsave(&rnp->lock, flags);
1347
	smp_mb__after_unlock_lock();
1348 1349
	rnp->boost_kthread_task = t;
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1350
	sp.sched_priority = RCU_BOOST_PRIO;
1351
	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1352
	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1353 1354 1355
	return 0;
}

1356 1357
static void rcu_kthread_do_work(void)
{
1358 1359
	rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
	rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
1360 1361 1362
	rcu_preempt_do_callbacks();
}

1363
static void rcu_cpu_kthread_setup(unsigned int cpu)
1364 1365 1366
{
	struct sched_param sp;

1367 1368
	sp.sched_priority = RCU_KTHREAD_PRIO;
	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1369 1370
}

1371
static void rcu_cpu_kthread_park(unsigned int cpu)
1372
{
1373
	per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1374 1375
}

1376
static int rcu_cpu_kthread_should_run(unsigned int cpu)
1377
{
1378
	return __this_cpu_read(rcu_cpu_has_work);
1379 1380 1381 1382
}

/*
 * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
1383 1384
 * RCU softirq used in flavors and configurations of RCU that do not
 * support RCU priority boosting.
1385
 */
1386
static void rcu_cpu_kthread(unsigned int cpu)
1387
{
1388 1389
	unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
	char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
1390
	int spincnt;
1391

1392
	for (spincnt = 0; spincnt < 10; spincnt++) {
1393
		trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1394 1395
		local_bh_disable();
		*statusp = RCU_KTHREAD_RUNNING;
1396 1397
		this_cpu_inc(rcu_cpu_kthread_loops);
		local_irq_disable();
1398 1399
		work = *workp;
		*workp = 0;
1400
		local_irq_enable();
1401 1402 1403
		if (work)
			rcu_kthread_do_work();
		local_bh_enable();
1404
		if (*workp == 0) {
1405
			trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1406 1407
			*statusp = RCU_KTHREAD_WAITING;
			return;
1408 1409
		}
	}
1410
	*statusp = RCU_KTHREAD_YIELDING;
1411
	trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1412
	schedule_timeout_interruptible(2);
1413
	trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1414
	*statusp = RCU_KTHREAD_WAITING;
1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425
}

/*
 * 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)
1427
{
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	struct task_struct *t = rnp->boost_kthread_task;
	unsigned long mask = rnp->qsmaskinit;
1430 1431 1432
	cpumask_var_t cm;
	int cpu;

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	if (!t)
1434
		return;
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1435
	if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1436 1437 1438 1439 1440 1441 1442 1443 1444 1445
		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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	set_cpus_allowed_ptr(t, cm);
1447 1448 1449
	free_cpumask_var(cm);
}

1450 1451 1452 1453 1454 1455 1456 1457
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,
};
1458 1459 1460 1461 1462 1463 1464

/*
 * Spawn all kthreads -- called as soon as the scheduler is running.
 */
static int __init rcu_spawn_kthreads(void)
{
	struct rcu_node *rnp;
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	int cpu;
1466

1467
	rcu_scheduler_fully_active = 1;
1468
	for_each_possible_cpu(cpu)
1469
		per_cpu(rcu_cpu_has_work, cpu) = 0;
1470
	BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1471 1472
	rnp = rcu_get_root(rcu_state_p);
	(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1473
	if (NUM_RCU_NODES > 1) {
1474 1475
		rcu_for_each_leaf_node(rcu_state_p, rnp)
			(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1476 1477 1478 1479 1480
	}
	return 0;
}
early_initcall(rcu_spawn_kthreads);

1481
static void rcu_prepare_kthreads(int cpu)
1482
{
1483
	struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
1484 1485 1486
	struct rcu_node *rnp = rdp->mynode;

	/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1487
	if (rcu_scheduler_fully_active)
1488
		(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1489 1490
}

1491 1492
#else /* #ifdef CONFIG_RCU_BOOST */

1493
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1494
{
1495
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1496 1497
}

1498
static void invoke_rcu_callbacks_kthread(void)
1499
{
1500
	WARN_ON_ONCE(1);
1501 1502
}

1503 1504 1505 1506 1507
static bool rcu_is_callbacks_kthread(void)
{
	return false;
}

1508 1509 1510 1511
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
}

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static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1513 1514 1515
{
}

1516 1517 1518 1519 1520 1521 1522
static int __init rcu_scheduler_really_started(void)
{
	rcu_scheduler_fully_active = 1;
	return 0;
}
early_initcall(rcu_scheduler_really_started);

1523
static void rcu_prepare_kthreads(int cpu)
1524 1525 1526
{
}

1527 1528
#endif /* #else #ifdef CONFIG_RCU_BOOST */

1529 1530 1531 1532 1533 1534 1535 1536
#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.
 *
1537 1538
 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
 * any flavor of RCU.
1539
 */
1540
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1541
int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1542
{
1543
	*delta_jiffies = ULONG_MAX;
1544
	return rcu_cpu_has_callbacks(cpu, NULL);
1545
}
1546
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1547 1548 1549 1550 1551 1552 1553 1554 1555

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

1556
/*
1557
 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1558 1559 1560 1561 1562 1563
 * is nothing.
 */
static void rcu_prepare_for_idle(int cpu)
{
}

1564 1565 1566 1567 1568 1569 1570 1571
/*
 * 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)
{
}

1572 1573
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */

1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588
/*
 * 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!
1589 1590 1591
 * 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.
1592 1593 1594 1595 1596
 *
 * 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.
 */
1597
#define RCU_IDLE_GP_DELAY 4		/* Roughly one grace period. */
1598
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ)	/* Roughly six seconds. */
1599

1600 1601 1602 1603
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);
1604

1605
extern int tick_nohz_active;
1606 1607

/*
1608 1609 1610
 * 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.
1611
 */
1612
static bool __maybe_unused rcu_try_advance_all_cbs(void)
1613
{
1614 1615
	bool cbs_ready = false;
	struct rcu_data *rdp;
1616
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1617 1618
	struct rcu_node *rnp;
	struct rcu_state *rsp;
1619

1620 1621 1622 1623 1624
	/* Exit early if we advanced recently. */
	if (jiffies == rdtp->last_advance_all)
		return 0;
	rdtp->last_advance_all = jiffies;

1625 1626 1627
	for_each_rcu_flavor(rsp) {
		rdp = this_cpu_ptr(rsp->rda);
		rnp = rdp->mynode;
1628

1629 1630 1631 1632 1633 1634 1635
		/*
		 * 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])
1636
			note_gp_changes(rsp, rdp);
1637

1638 1639 1640 1641
		if (cpu_has_callbacks_ready_to_invoke(rdp))
			cbs_ready = true;
	}
	return cbs_ready;
1642 1643
}

1644
/*
1645 1646 1647 1648
 * 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.
1649
 *
1650
 * The caller must have disabled interrupts.
1651
 */
1652
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1653
int rcu_needs_cpu(int cpu, unsigned long *dj)
1654 1655 1656
{
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);

1657 1658 1659
	/* Snapshot to detect later posting of non-lazy callback. */
	rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;

1660
	/* If no callbacks, RCU doesn't need the CPU. */
1661 1662
	if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
		*dj = ULONG_MAX;
1663 1664
		return 0;
	}
1665 1666 1667 1668 1669

	/* Attempt to advance callbacks. */
	if (rcu_try_advance_all_cbs()) {
		/* Some ready to invoke, so initiate later invocation. */
		invoke_rcu_core();
1670 1671
		return 1;
	}
1672 1673 1674
	rdtp->last_accelerate = jiffies;

	/* Request timer delay depending on laziness, and round. */
1675
	if (!rdtp->all_lazy) {
1676 1677
		*dj = round_up(rcu_idle_gp_delay + jiffies,
			       rcu_idle_gp_delay) - jiffies;
1678
	} else {
1679
		*dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1680
	}
1681 1682
	return 0;
}
1683
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1684

1685
/*
1686 1687 1688 1689 1690 1691
 * 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.
1692 1693
 *
 * The caller must have disabled interrupts.
1694
 */
1695
static void rcu_prepare_for_idle(int cpu)
1696
{
1697
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1698
	bool needwake;
1699
	struct rcu_data *rdp;
1700
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1701 1702
	struct rcu_node *rnp;
	struct rcu_state *rsp;
1703 1704 1705
	int tne;

	/* Handle nohz enablement switches conservatively. */
1706
	tne = ACCESS_ONCE(tick_nohz_active);
1707
	if (tne != rdtp->tick_nohz_enabled_snap) {
1708
		if (rcu_cpu_has_callbacks(cpu, NULL))
1709 1710 1711 1712 1713 1714
			invoke_rcu_core(); /* force nohz to see update. */
		rdtp->tick_nohz_enabled_snap = tne;
		return;
	}
	if (!tne)
		return;
1715

1716
	/* If this is a no-CBs CPU, no callbacks, just return. */
1717
	if (rcu_is_nocb_cpu(cpu))
1718 1719
		return;

1720
	/*
1721 1722 1723
	 * 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.
1724
	 */
1725 1726
	if (rdtp->all_lazy &&
	    rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1727 1728
		rdtp->all_lazy = false;
		rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1729
		invoke_rcu_core();
1730 1731 1732
		return;
	}

1733
	/*
1734 1735
	 * If we have not yet accelerated this jiffy, accelerate all
	 * callbacks on this CPU.
1736
	 */
1737
	if (rdtp->last_accelerate == jiffies)
1738
		return;
1739 1740 1741 1742 1743 1744 1745
	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. */
1746
		smp_mb__after_unlock_lock();
1747
		needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
1748
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1749 1750
		if (needwake)
			rcu_gp_kthread_wake(rsp);
1751
	}
1752
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1753
}
1754

1755 1756 1757 1758 1759 1760 1761
/*
 * 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)
{
1762
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1763
	if (rcu_is_nocb_cpu(cpu))
1764
		return;
1765 1766
	if (rcu_try_advance_all_cbs())
		invoke_rcu_core();
1767
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1768 1769
}

1770
/*
1771 1772 1773 1774 1775 1776
 * 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().
1777 1778 1779
 */
static void rcu_idle_count_callbacks_posted(void)
{
1780
	__this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1781 1782
}

1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811
/*
 * 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) {
1812
		rdp = raw_cpu_ptr(rsp->rda);
1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833
		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);
1834
	smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865

	/*
	 * Prevent premature wakeup: ensure that all increments happen
	 * before there is a chance of the counter reaching zero.
	 */
	atomic_set(&oom_callback_count, 1);

	get_online_cpus();
	for_each_online_cpu(cpu) {
		smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
		cond_resched();
	}
	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);

1866
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1867 1868 1869 1870 1871 1872 1873

#ifdef CONFIG_RCU_CPU_STALL_INFO

#ifdef CONFIG_RCU_FAST_NO_HZ

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
1874
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1875
	unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1876

1877 1878 1879 1880 1881
	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');
1882 1883 1884 1885 1886 1887
}

#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
1888
	*cp = '\0';
1889 1890 1891 1892 1893 1894 1895
}

#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */

/* Initiate the stall-info list. */
static void print_cpu_stall_info_begin(void)
{
1896
	pr_cont("\n");
1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926
}

/*
 * 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);
1927
	pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
1928 1929 1930
	       cpu, ticks_value, ticks_title,
	       atomic_read(&rdtp->dynticks) & 0xfff,
	       rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1931
	       rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1932 1933 1934 1935 1936 1937
	       fast_no_hz);
}

/* Terminate the stall-info list. */
static void print_cpu_stall_info_end(void)
{
1938
	pr_err("\t");
1939 1940 1941 1942 1943 1944
}

/* Zero ->ticks_this_gp for all flavors of RCU. */
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
	rdp->ticks_this_gp = 0;
1945
	rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1946 1947 1948 1949 1950
}

/* Increment ->ticks_this_gp for all flavors of RCU. */
static void increment_cpu_stall_ticks(void)
{
1951 1952 1953
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
1954
		raw_cpu_inc(rsp->rda->ticks_this_gp);
1955 1956 1957 1958 1959 1960
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

static void print_cpu_stall_info_begin(void)
{
1961
	pr_cont(" {");
1962 1963 1964 1965
}

static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
1966
	pr_cont(" %d", cpu);
1967 1968 1969 1970
}

static void print_cpu_stall_info_end(void)
{
1971
	pr_cont("} ");
1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982
}

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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1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016

#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);

2017 2018 2019 2020 2021 2022 2023
static int __init parse_rcu_nocb_poll(char *arg)
{
	rcu_nocb_poll = 1;
	return 0;
}
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);

2024
/*
2025 2026
 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
 * grace period.
2027
 */
2028
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2029
{
2030
	wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
2031 2032 2033
}

/*
2034
 * Set the root rcu_node structure's ->need_future_gp field
2035 2036 2037 2038 2039
 * 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.
2040
 */
2041 2042
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
{
2043
	rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
2044 2045 2046
}

static void rcu_init_one_nocb(struct rcu_node *rnp)
2047
{
2048 2049
	init_waitqueue_head(&rnp->nocb_gp_wq[0]);
	init_waitqueue_head(&rnp->nocb_gp_wq[1]);
2050 2051
}

2052
#ifndef CONFIG_RCU_NOCB_CPU_ALL
L
Liu Ping Fan 已提交
2053
/* Is the specified CPU a no-CBs CPU? */
2054
bool rcu_is_nocb_cpu(int cpu)
P
Paul E. McKenney 已提交
2055 2056 2057 2058 2059
{
	if (have_rcu_nocb_mask)
		return cpumask_test_cpu(cpu, rcu_nocb_mask);
	return false;
}
2060
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
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2061 2062 2063 2064 2065 2066 2067 2068 2069 2070 2071 2072

/*
 * 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,
2073 2074
				    int rhcount, int rhcount_lazy,
				    unsigned long flags)
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Paul E. McKenney 已提交
2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086 2087
{
	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);

	/* If we are not being polled and there is a kthread, awaken it ... */
	t = ACCESS_ONCE(rdp->nocb_kthread);
2088
	if (rcu_nocb_poll || !t) {
2089 2090
		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
				    TPS("WakeNotPoll"));
P
Paul E. McKenney 已提交
2091
		return;
2092
	}
P
Paul E. McKenney 已提交
2093 2094
	len = atomic_long_read(&rdp->nocb_q_count);
	if (old_rhpp == &rdp->nocb_head) {
2095 2096 2097 2098 2099 2100 2101 2102 2103
		if (!irqs_disabled_flags(flags)) {
			wake_up(&rdp->nocb_wq); /* ... if queue was empty ... */
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    TPS("WakeEmpty"));
		} else {
			rdp->nocb_defer_wakeup = true;
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    TPS("WakeEmptyIsDeferred"));
		}
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Paul E. McKenney 已提交
2104 2105 2106 2107
		rdp->qlen_last_fqs_check = 0;
	} else if (len > rdp->qlen_last_fqs_check + qhimark) {
		wake_up_process(t); /* ... or if many callbacks queued. */
		rdp->qlen_last_fqs_check = LONG_MAX / 2;
2108 2109 2110
		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf"));
	} else {
		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
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Paul E. McKenney 已提交
2111 2112 2113 2114 2115 2116 2117 2118 2119 2120 2121 2122 2123 2124
	}
	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,
2125
			    bool lazy, unsigned long flags)
P
Paul E. McKenney 已提交
2126 2127
{

2128
	if (!rcu_is_nocb_cpu(rdp->cpu))
P
Paul E. McKenney 已提交
2129
		return 0;
2130
	__call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
2131 2132 2133
	if (__is_kfree_rcu_offset((unsigned long)rhp->func))
		trace_rcu_kfree_callback(rdp->rsp->name, rhp,
					 (unsigned long)rhp->func,
2134 2135
					 -atomic_long_read(&rdp->nocb_q_count_lazy),
					 -atomic_long_read(&rdp->nocb_q_count));
2136 2137
	else
		trace_rcu_callback(rdp->rsp->name, rhp,
2138 2139
				   -atomic_long_read(&rdp->nocb_q_count_lazy),
				   -atomic_long_read(&rdp->nocb_q_count));
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Paul E. McKenney 已提交
2140 2141 2142 2143 2144 2145 2146 2147
	return 1;
}

/*
 * 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,
2148 2149
						     struct rcu_data *rdp,
						     unsigned long flags)
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Paul E. McKenney 已提交
2150 2151 2152 2153 2154
{
	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. */
2155
	if (!rcu_is_nocb_cpu(smp_processor_id()))
P
Paul E. McKenney 已提交
2156 2157 2158 2159 2160 2161 2162
		return 0;
	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,
2163
					rsp->orphan_donetail, ql, qll, flags);
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Paul E. McKenney 已提交
2164 2165 2166 2167 2168 2169
		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,
2170
					rsp->orphan_nxttail, ql, qll, flags);
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Paul E. McKenney 已提交
2171 2172 2173 2174 2175 2176 2177 2178
		ql = qll = 0;
		rsp->orphan_nxtlist = NULL;
		rsp->orphan_nxttail = &rsp->orphan_nxtlist;
	}
	return 1;
}

/*
2179 2180
 * If necessary, kick off a new grace period, and either way wait
 * for a subsequent grace period to complete.
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2181
 */
2182
static void rcu_nocb_wait_gp(struct rcu_data *rdp)
P
Paul E. McKenney 已提交
2183
{
2184
	unsigned long c;
2185
	bool d;
2186
	unsigned long flags;
2187
	bool needwake;
2188 2189 2190
	struct rcu_node *rnp = rdp->mynode;

	raw_spin_lock_irqsave(&rnp->lock, flags);
2191
	smp_mb__after_unlock_lock();
2192
	needwake = rcu_start_future_gp(rnp, rdp, &c);
2193
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
2194 2195
	if (needwake)
		rcu_gp_kthread_wake(rdp->rsp);
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	/*
2198 2199
	 * Wait for the grace period.  Do so interruptibly to avoid messing
	 * up the load average.
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	 */
2201
	trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
2202
	for (;;) {
2203 2204 2205 2206
		wait_event_interruptible(
			rnp->nocb_gp_wq[c & 0x1],
			(d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
		if (likely(d))
2207
			break;
2208
		flush_signals(current);
2209
		trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
2210
	}
2211
	trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
2212
	smp_mb(); /* Ensure that CB invocation happens after GP end. */
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}

/*
 * Per-rcu_data kthread, but only for no-CBs CPUs.  Each kthread invokes
 * callbacks queued by the corresponding no-CBs CPU.
 */
static int rcu_nocb_kthread(void *arg)
{
	int c, cl;
2222
	bool firsttime = 1;
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	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 (;;) {
		/* If not polling, wait for next batch of callbacks. */
2231 2232 2233
		if (!rcu_nocb_poll) {
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    TPS("Sleep"));
2234
			wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
2235
			/* Memory barrier provide by xchg() below. */
2236 2237 2238 2239 2240
		} else if (firsttime) {
			firsttime = 0;
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    TPS("Poll"));
		}
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		list = ACCESS_ONCE(rdp->nocb_head);
		if (!list) {
2243 2244 2245
			if (!rcu_nocb_poll)
				trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
						    TPS("WokeEmpty"));
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			schedule_timeout_interruptible(1);
2247
			flush_signals(current);
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			continue;
		}
2250
		firsttime = 1;
2251 2252
		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
				    TPS("WokeNonEmpty"));
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		/*
		 * Extract queued callbacks, update counts, and wait
		 * for a grace period to elapse.
		 */
		ACCESS_ONCE(rdp->nocb_head) = NULL;
		tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
		c = atomic_long_xchg(&rdp->nocb_q_count, 0);
		cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
		ACCESS_ONCE(rdp->nocb_p_count) += c;
		ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl;
2264
		rcu_nocb_wait_gp(rdp);
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		/* 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) {
2273 2274
				trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
						    TPS("WaitQueue"));
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				schedule_timeout_interruptible(1);
2276 2277
				trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
						    TPS("WokeQueue"));
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				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);
		ACCESS_ONCE(rdp->nocb_p_count) -= c;
		ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
2291
		rdp->n_nocbs_invoked += c;
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	}
	return 0;
}

2296 2297 2298 2299 2300 2301 2302 2303 2304 2305 2306 2307 2308 2309 2310 2311
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
{
	return ACCESS_ONCE(rdp->nocb_defer_wakeup);
}

/* Do a deferred wakeup of rcu_nocb_kthread(). */
static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
{
	if (!rcu_nocb_need_deferred_wakeup(rdp))
		return;
	ACCESS_ONCE(rdp->nocb_defer_wakeup) = false;
	wake_up(&rdp->nocb_wq);
	trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWakeEmpty"));
}

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/* 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);
}

/* Create a kthread for each RCU flavor for each no-CBs CPU. */
static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
{
	int cpu;
	struct rcu_data *rdp;
	struct task_struct *t;

	if (rcu_nocb_mask == NULL)
		return;
	for_each_cpu(cpu, rcu_nocb_mask) {
		rdp = per_cpu_ptr(rsp->rda, cpu);
2330 2331
		t = kthread_run(rcu_nocb_kthread, rdp,
				"rcuo%c/%d", rsp->abbr, cpu);
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		BUG_ON(IS_ERR(t));
		ACCESS_ONCE(rdp->nocb_kthread) = t;
	}
}

/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2338
static bool init_nocb_callback_list(struct rcu_data *rdp)
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{
	if (rcu_nocb_mask == NULL ||
	    !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
2342
		return false;
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	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2344
	return true;
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}

2347 2348
#else /* #ifdef CONFIG_RCU_NOCB_CPU */

2349
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
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{
}

2353 2354 2355 2356 2357 2358 2359
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
{
}

static void rcu_init_one_nocb(struct rcu_node *rnp)
{
}
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static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2362
			    bool lazy, unsigned long flags)
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{
	return 0;
}

static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2368 2369
						     struct rcu_data *rdp,
						     unsigned long flags)
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{
	return 0;
}

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

2378 2379 2380 2381 2382 2383 2384 2385 2386
static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
{
	return false;
}

static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
{
}

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static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
{
}

2391
static bool init_nocb_callback_list(struct rcu_data *rdp)
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{
2393
	return false;
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}

#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2397 2398 2399 2400 2401 2402 2403 2404 2405 2406

/*
 * 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.
 */
2407
static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
2408 2409 2410 2411 2412 2413
{
#ifdef CONFIG_NO_HZ_FULL
	if (tick_nohz_full_cpu(cpu))
		smp_send_reschedule(cpu);
#endif /* #ifdef CONFIG_NO_HZ_FULL */
}
2414 2415 2416 2417


#ifdef CONFIG_NO_HZ_FULL_SYSIDLE

2418 2419 2420 2421 2422
/*
 * Define RCU flavor that holds sysidle state.  This needs to be the
 * most active flavor of RCU.
 */
#ifdef CONFIG_PREEMPT_RCU
2423
static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
2424
#else /* #ifdef CONFIG_PREEMPT_RCU */
2425
static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
2426 2427
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */

2428
static int full_sysidle_state;		/* Current system-idle state. */
2429 2430 2431 2432 2433 2434
#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. */

2435 2436 2437 2438 2439 2440 2441 2442 2443 2444 2445 2446 2447 2448 2449 2450 2451 2452 2453 2454 2455 2456 2457 2458 2459 2460 2461 2462 2463 2464
/*
 * Invoked to note exit from irq or task transition to idle.  Note that
 * usermode execution does -not- count as idle here!  After all, we want
 * to detect full-system idle states, not RCU quiescent states and grace
 * periods.  The caller must have disabled interrupts.
 */
static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
{
	unsigned long j;

	/* 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;
2465
	smp_mb__before_atomic();
2466
	atomic_inc(&rdtp->dynticks_idle);
2467
	smp_mb__after_atomic();
2468 2469 2470
	WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
}

2471 2472 2473 2474 2475 2476 2477 2478 2479 2480 2481 2482 2483 2484 2485 2486 2487 2488 2489 2490 2491 2492 2493 2494 2495 2496 2497 2498 2499 2500 2501 2502
/*
 * 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. */
}

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
/*
 * Invoked to note entry to irq or task transition from idle.  Note that
 * usermode execution does -not- count as idle here!  The caller must
 * have disabled interrupts.
 */
static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
{
	/* 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. */
2532
	smp_mb__before_atomic();
2533
	atomic_inc(&rdtp->dynticks_idle);
2534
	smp_mb__after_atomic();
2535
	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
2536 2537 2538 2539 2540 2541 2542 2543 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

	/*
	 * 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;

	/*
	 * If some other CPU has already reported non-idle, if this is
	 * not the flavor of RCU that tracks sysidle state, or if this
	 * is an offline or the timekeeping CPU, nothing to do.
	 */
	if (!*isidle || rdp->rsp != rcu_sysidle_state ||
	    cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
		return;
2572 2573
	if (rcu_gp_in_progress(rdp->rsp))
		WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
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 2617 2618 2619 2620 2621 2622 2623 2624 2625 2626 2627 2628 2629 2630 2631 2632 2633 2634 2635 2636 2637 2638 2639 2640 2641 2642 2643 2644 2645 2646 2647 2648 2649 2650 2651 2652 2653 2654 2655 2656 2657 2658 2659 2660 2661

	/* Pick up current idle and NMI-nesting counter and check. */
	cur = atomic_read(&rdtp->dynticks_idle);
	if (cur & 0x1) {
		*isidle = false; /* We are not idle! */
		return;
	}
	smp_mb(); /* Read counters before timestamps. */

	/* Pick up timestamps. */
	j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
	/* If this CPU entered idle more recently, update maxj timestamp. */
	if (ULONG_CMP_LT(*maxj, j))
		*maxj = j;
}

/*
 * Is this the flavor of RCU that is handling full-system idle?
 */
static bool is_sysidle_rcu_state(struct rcu_state *rsp)
{
	return rsp == rcu_sysidle_state;
}

/*
 * 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();
2662 2663
	if (full_sysidle_state > RCU_SYSIDLE_SHORT)
		ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
2664 2665 2666 2667 2668 2669 2670 2671 2672 2673 2674 2675 2676 2677 2678 2679 2680 2681 2682 2683 2684 2685 2686 2687 2688 2689 2690 2691 2692 2693 2694 2695 2696 2697 2698 2699 2700 2701 2702 2703 2704 2705 2706 2707 2708 2709 2710 2711 2712 2713 2714 2715 2716 2717 2718 2719 2720 2721 2722 2723 2724 2725 2726 2727 2728 2729 2730 2731 2732 2733 2734 2735 2736 2737 2738 2739 2740 2741 2742 2743 2744 2745 2746 2747 2748 2749 2750 2751 2752 2753 2754 2755 2756 2757 2758 2759 2760 2761 2762 2763 2764 2765 2766 2767 2768 2769 2770 2771 2772 2773 2774 2775 2776 2777 2778
}

/*
 * Update the sysidle state based on the results of a force-quiescent-state
 * scan of the CPUs' dyntick-idle state.
 */
static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
			       unsigned long maxj, bool gpkt)
{
	if (rsp != rcu_sysidle_state)
		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)
{
	rcu_sysidle_report(rsp, isidle, maxj, true);
}

/* Callback and function for forcing an RCU grace period. */
struct rcu_sysidle_head {
	struct rcu_head rh;
	int inuse;
};

static void rcu_sysidle_cb(struct rcu_head *rhp)
{
	struct rcu_sysidle_head *rshp;

	/*
	 * The following memory barrier is needed to replace the
	 * memory barriers that would normally be in the memory
	 * allocator.
	 */
	smp_mb();  /* grace period precedes setting inuse. */

	rshp = container_of(rhp, struct rcu_sysidle_head, rh);
	ACCESS_ONCE(rshp->inuse) = 0;
}

/*
 * Check to see if the system is fully idle, other than the timekeeping CPU.
 * The caller must have disabled interrupts.
 */
bool rcu_sys_is_idle(void)
{
	static struct rcu_sysidle_head rsh;
	int rss = ACCESS_ONCE(full_sysidle_state);

	if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
		return false;

	/* Handle small-system case by doing a full scan of CPUs. */
	if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
		int oldrss = rss - 1;

		/*
		 * One pass to advance to each state up to _FULL.
		 * Give up if any pass fails to advance the state.
		 */
		while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
			int cpu;
			bool isidle = true;
			unsigned long maxj = jiffies - ULONG_MAX / 4;
			struct rcu_data *rdp;

			/* Scan all the CPUs looking for nonidle CPUs. */
			for_each_possible_cpu(cpu) {
				rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
				rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
				if (!isidle)
					break;
			}
			rcu_sysidle_report(rcu_sysidle_state,
					   isidle, maxj, false);
			oldrss = rss;
			rss = ACCESS_ONCE(full_sysidle_state);
		}
	}

	/* If this is the first observation of an idle period, record it. */
	if (rss == RCU_SYSIDLE_FULL) {
		rss = cmpxchg(&full_sysidle_state,
			      RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
		return rss == RCU_SYSIDLE_FULL;
	}

	smp_mb(); /* ensure rss load happens before later caller actions. */

	/* If already fully idle, tell the caller (in case of races). */
	if (rss == RCU_SYSIDLE_FULL_NOTED)
		return true;

	/*
	 * If we aren't there yet, and a grace period is not in flight,
	 * initiate a grace period.  Either way, tell the caller that
	 * we are not there yet.  We use an xchg() rather than an assignment
	 * to make up for the memory barriers that would otherwise be
	 * provided by the memory allocator.
	 */
	if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
	    !rcu_gp_in_progress(rcu_sysidle_state) &&
	    !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
		call_rcu(&rsh.rh, rcu_sysidle_cb);
	return false;
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}

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/*
 * 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 */

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static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
{
}

static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
{
}

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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)
{
}

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static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
{
}

#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
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/*
 * 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
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 * CONFIG_RCU_NOCB_CPU CPUs.
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 */
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;
}
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/*
 * Bind the grace-period kthread for the sysidle flavor of RCU to the
 * timekeeping CPU.
 */
static void rcu_bind_gp_kthread(void)
{
#ifdef CONFIG_NO_HZ_FULL
	int cpu = ACCESS_ONCE(tick_do_timer_cpu);

	if (cpu < 0 || cpu >= nr_cpu_ids)
		return;
	if (raw_smp_processor_id() != cpu)
		set_cpus_allowed_ptr(current, cpumask_of(cpu));
#endif /* #ifdef CONFIG_NO_HZ_FULL */
}