rcutree_plugin.h 67.6 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
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * 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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#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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/*
 * 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
	printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n");
#endif
#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
	printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
	       CONFIG_RCU_FANOUT);
#endif
#ifdef CONFIG_RCU_FANOUT_EXACT
	printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n");
#endif
#ifdef CONFIG_RCU_FAST_NO_HZ
	printk(KERN_INFO
	       "\tRCU dyntick-idle grace-period acceleration is enabled.\n");
#endif
#ifdef CONFIG_PROVE_RCU
	printk(KERN_INFO "\tRCU lockdep checking is enabled.\n");
#endif
#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
	printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
#endif
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#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
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	printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n");
#endif
#if defined(CONFIG_RCU_CPU_STALL_INFO)
	printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n");
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#endif
#if NUM_RCU_LVL_4 != 0
	printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n");
#endif
}

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#ifdef CONFIG_TREE_PREEMPT_RCU

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struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt);
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DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
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static struct rcu_state *rcu_state = &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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	printk(KERN_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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/*
 * Force a quiescent state for preemptible RCU.
 */
void rcu_force_quiescent_state(void)
{
	force_quiescent_state(&rcu_preempt_state, 0);
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);

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/*
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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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	rdp->passed_quiesce_gpnum = rdp->gpnum;
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	barrier();
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	if (rdp->passed_quiesce == 0)
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		trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "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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		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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	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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	}

	/* Hardware IRQ handlers cannot block. */
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	if (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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			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("rcu_preempt",
						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)) {
			trace_rcu_quiescent_state_report("preempt_rcu",
							 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
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
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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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	if (!rcu_preempt_blocked_readers_cgp(rnp))
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		return;
	raw_spin_lock_irqsave(&rnp->lock, flags);
	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)
{
	printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
	       rnp->level, rnp->grplo, rnp->grphi);
}

static void rcu_print_task_stall_end(void)
{
	printk(KERN_CONT "\n");
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
}

static void rcu_print_task_stall_end(void)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */

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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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		printk(KERN_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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/*
 * Suppress preemptible RCU's CPU stall warnings by pushing the
 * time of the next stall-warning message comfortably far into the
 * future.
 */
static void rcu_preempt_stall_reset(void)
{
	rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2;
}

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/*
 * Check that the list of blocked tasks for the newly completed grace
 * period is in fact empty.  It is a serious bug to complete a grace
 * period that still has RCU readers blocked!  This function must be
 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
 * must be held by the caller.
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 *
 * Also, if there are blocked tasks on the list, they automatically
 * block the newly created grace period, so set up ->gp_tasks accordingly.
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 */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
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	WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
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	if (!list_empty(&rnp->blkd_tasks))
		rnp->gp_tasks = rnp->blkd_tasks.next;
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	WARN_ON_ONCE(rnp->qsmask);
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}

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#ifdef CONFIG_HOTPLUG_CPU

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/*
 * Handle tasklist migration for case in which all CPUs covered by the
 * specified rcu_node have gone offline.  Move them up to the root
 * rcu_node.  The reason for not just moving them to the immediate
 * parent is to remove the need for rcu_read_unlock_special() to
 * make more than two attempts to acquire the target rcu_node's lock.
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 * Returns true if there were tasks blocking the current RCU grace
 * period.
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 *
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 * Returns 1 if there was previously a task blocking the current grace
 * period on the specified rcu_node structure.
 *
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 * The caller must hold rnp->lock with irqs disabled.
 */
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static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
				     struct rcu_node *rnp,
				     struct rcu_data *rdp)
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{
	struct list_head *lp;
	struct list_head *lp_root;
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	int retval = 0;
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	struct rcu_node *rnp_root = rcu_get_root(rsp);
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	struct task_struct *t;
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	if (rnp == rnp_root) {
		WARN_ONCE(1, "Last CPU thought to be offlined?");
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		return 0;  /* Shouldn't happen: at least one CPU online. */
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	}
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	/* If we are on an internal node, complain bitterly. */
	WARN_ON_ONCE(rnp != rdp->mynode);
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	/*
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	 * Move tasks up to root rcu_node.  Don't try to get fancy for
	 * this corner-case operation -- just put this node's tasks
	 * at the head of the root node's list, and update the root node's
	 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
	 * if non-NULL.  This might result in waiting for more tasks than
	 * absolutely necessary, but this is a good performance/complexity
	 * tradeoff.
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	 */
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	if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
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		retval |= RCU_OFL_TASKS_NORM_GP;
	if (rcu_preempted_readers_exp(rnp))
		retval |= RCU_OFL_TASKS_EXP_GP;
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	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 */
		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;
584 585 586 587
#ifdef CONFIG_RCU_BOOST
		if (&t->rcu_node_entry == rnp->boost_tasks)
			rnp_root->boost_tasks = rnp->boost_tasks;
#endif /* #ifdef CONFIG_RCU_BOOST */
588
		raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
589
	}
590 591 592 593 594 595 596 597 598 599

#ifdef CONFIG_RCU_BOOST
	/* In case root is being boosted and leaf is not. */
	raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
	if (rnp_root->boost_tasks != NULL &&
	    rnp_root->boost_tasks != rnp_root->gp_tasks)
		rnp_root->boost_tasks = rnp_root->gp_tasks;
	raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
#endif /* #ifdef CONFIG_RCU_BOOST */

600 601
	rnp->gp_tasks = NULL;
	rnp->exp_tasks = NULL;
602
	return retval;
603 604
}

605 606
#endif /* #ifdef CONFIG_HOTPLUG_CPU */

607
/*
P
Paul E. McKenney 已提交
608
 * Do CPU-offline processing for preemptible RCU.
609
 */
610
static void rcu_preempt_cleanup_dead_cpu(int cpu)
611
{
612
	rcu_cleanup_dead_cpu(cpu, &rcu_preempt_state);
613 614
}

615 616 617 618 619 620 621 622 623 624 625 626
/*
 * 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) {
627
		rcu_preempt_qs(cpu);
628 629
		return;
	}
630 631
	if (t->rcu_read_lock_nesting > 0 &&
	    per_cpu(rcu_preempt_data, cpu).qs_pending)
632
		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
633 634 635
}

/*
P
Paul E. McKenney 已提交
636
 * Process callbacks for preemptible RCU.
637 638 639 640 641 642 643
 */
static void rcu_preempt_process_callbacks(void)
{
	__rcu_process_callbacks(&rcu_preempt_state,
				&__get_cpu_var(rcu_preempt_data));
}

644 645
#ifdef CONFIG_RCU_BOOST

646 647 648 649 650
static void rcu_preempt_do_callbacks(void)
{
	rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
}

651 652
#endif /* #ifdef CONFIG_RCU_BOOST */

653
/*
P
Paul E. McKenney 已提交
654
 * Queue a preemptible-RCU callback for invocation after a grace period.
655 656 657
 */
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
658
	__call_rcu(head, func, &rcu_preempt_state, 0);
659 660 661
}
EXPORT_SYMBOL_GPL(call_rcu);

662 663 664 665 666 667 668 669 670 671 672 673 674 675
/*
 * Queue an RCU callback for lazy invocation after a grace period.
 * This will likely be later named something like "call_rcu_lazy()",
 * but this change will require some way of tagging the lazy RCU
 * callbacks in the list of pending callbacks.  Until then, this
 * function may only be called from __kfree_rcu().
 */
void kfree_call_rcu(struct rcu_head *head,
		    void (*func)(struct rcu_head *rcu))
{
	__call_rcu(head, func, &rcu_preempt_state, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);

676 677 678 679 680
/**
 * 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
681 682 683 684 685
 * 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.
686 687 688
 */
void synchronize_rcu(void)
{
689 690 691 692
	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");
693 694
	if (!rcu_scheduler_active)
		return;
695
	wait_rcu_gp(call_rcu);
696 697 698
}
EXPORT_SYMBOL_GPL(synchronize_rcu);

699 700 701 702 703 704 705 706 707 708 709 710
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
static long sync_rcu_preempt_exp_count;
static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);

/*
 * Return non-zero if there are any tasks in RCU read-side critical
 * sections blocking the current preemptible-RCU expedited grace period.
 * If there is no preemptible-RCU expedited grace period currently in
 * progress, returns zero unconditionally.
 */
static int rcu_preempted_readers_exp(struct rcu_node *rnp)
{
711
	return rnp->exp_tasks != NULL;
712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736
}

/*
 * 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!)
 *
737 738 739
 * Most callers will set the "wake" flag, but the task initiating the
 * expedited grace period need not wake itself.
 *
740 741
 * Caller must hold sync_rcu_preempt_exp_mutex.
 */
742 743
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
			       bool wake)
744 745 746 747
{
	unsigned long flags;
	unsigned long mask;

P
Paul E. McKenney 已提交
748
	raw_spin_lock_irqsave(&rnp->lock, flags);
749
	for (;;) {
750 751
		if (!sync_rcu_preempt_exp_done(rnp)) {
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
752
			break;
753
		}
754
		if (rnp->parent == NULL) {
755
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
756 757
			if (wake)
				wake_up(&sync_rcu_preempt_exp_wq);
758 759 760
			break;
		}
		mask = rnp->grpmask;
P
Paul E. McKenney 已提交
761
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
762
		rnp = rnp->parent;
P
Paul E. McKenney 已提交
763
		raw_spin_lock(&rnp->lock); /* irqs already disabled */
764 765 766 767 768 769 770 771 772 773 774 775 776 777
		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.
 *
 * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock.
 */
static void
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
{
778
	unsigned long flags;
779
	int must_wait = 0;
780

781 782 783 784
	raw_spin_lock_irqsave(&rnp->lock, flags);
	if (list_empty(&rnp->blkd_tasks))
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
	else {
785
		rnp->exp_tasks = rnp->blkd_tasks.next;
786
		rcu_initiate_boost(rnp, flags);  /* releases rnp->lock */
787 788
		must_wait = 1;
	}
789
	if (!must_wait)
790
		rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
791 792
}

793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808
/**
 * 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.
809 810 811
 */
void synchronize_rcu_expedited(void)
{
812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839
	unsigned long flags;
	struct rcu_node *rnp;
	struct rcu_state *rsp = &rcu_preempt_state;
	long snap;
	int trycount = 0;

	smp_mb(); /* Caller's modifications seen first by other CPUs. */
	snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
	smp_mb(); /* Above access cannot bleed into critical section. */

	/*
	 * Acquire lock, falling back to synchronize_rcu() if too many
	 * lock-acquisition failures.  Of course, if someone does the
	 * expedited grace period for us, just leave.
	 */
	while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
		if (trycount++ < 10)
			udelay(trycount * num_online_cpus());
		else {
			synchronize_rcu();
			return;
		}
		if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
			goto mb_ret; /* Others did our work for us. */
	}
	if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
		goto unlock_mb_ret; /* Others did our work for us. */

840
	/* force all RCU readers onto ->blkd_tasks lists. */
841 842
	synchronize_sched_expedited();

P
Paul E. McKenney 已提交
843
	raw_spin_lock_irqsave(&rsp->onofflock, flags);
844 845 846

	/* Initialize ->expmask for all non-leaf rcu_node structures. */
	rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
P
Paul E. McKenney 已提交
847
		raw_spin_lock(&rnp->lock); /* irqs already disabled. */
848
		rnp->expmask = rnp->qsmaskinit;
P
Paul E. McKenney 已提交
849
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
850 851
	}

852
	/* Snapshot current state of ->blkd_tasks lists. */
853 854 855 856 857
	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));

P
Paul E. McKenney 已提交
858
	raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
859

860
	/* Wait for snapshotted ->blkd_tasks lists to drain. */
861 862 863 864 865 866 867 868 869 870 871
	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. */
872 873 874
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

875
/*
P
Paul E. McKenney 已提交
876
 * Check to see if there is any immediate preemptible-RCU-related work
877 878 879 880 881 882 883 884 885
 * to be done.
 */
static int rcu_preempt_pending(int cpu)
{
	return __rcu_pending(&rcu_preempt_state,
			     &per_cpu(rcu_preempt_data, cpu));
}

/*
886
 * Does preemptible RCU have callbacks on this CPU?
887
 */
888
static int rcu_preempt_cpu_has_callbacks(int cpu)
889 890 891 892
{
	return !!per_cpu(rcu_preempt_data, cpu).nxtlist;
}

893 894 895 896 897 898 899 900 901
/**
 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
 */
void rcu_barrier(void)
{
	_rcu_barrier(&rcu_preempt_state, call_rcu);
}
EXPORT_SYMBOL_GPL(rcu_barrier);

902
/*
P
Paul E. McKenney 已提交
903
 * Initialize preemptible RCU's per-CPU data.
904 905 906 907 908 909
 */
static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
{
	rcu_init_percpu_data(cpu, &rcu_preempt_state, 1);
}

910
/*
911 912
 * Move preemptible RCU's callbacks from dying CPU to other online CPU
 * and record a quiescent state.
913
 */
914
static void rcu_preempt_cleanup_dying_cpu(void)
915
{
916
	rcu_cleanup_dying_cpu(&rcu_preempt_state);
917 918
}

919
/*
P
Paul E. McKenney 已提交
920
 * Initialize preemptible RCU's state structures.
921 922 923
 */
static void __init __rcu_init_preempt(void)
{
924
	rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
925 926
}

927 928
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */

929 930
static struct rcu_state *rcu_state = &rcu_sched_state;

931 932 933
/*
 * Tell them what RCU they are running.
 */
934
static void __init rcu_bootup_announce(void)
935 936
{
	printk(KERN_INFO "Hierarchical RCU implementation.\n");
937
	rcu_bootup_announce_oddness();
938 939 940 941 942 943 944 945 946 947 948
}

/*
 * 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);

949 950 951 952 953 954 955 956 957 958
/*
 * Force a quiescent state for RCU, which, because there is no preemptible
 * RCU, becomes the same as rcu-sched.
 */
void rcu_force_quiescent_state(void)
{
	rcu_sched_force_quiescent_state();
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);

959 960 961 962 963 964 965 966
/*
 * 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)
{
}

967
/*
P
Paul E. McKenney 已提交
968
 * Because preemptible RCU does not exist, there are never any preempted
969 970
 * RCU readers.
 */
971
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
972 973 974 975
{
	return 0;
}

976 977 978
#ifdef CONFIG_HOTPLUG_CPU

/* Because preemptible RCU does not exist, no quieting of tasks. */
P
Paul E. McKenney 已提交
979
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
980
{
P
Paul E. McKenney 已提交
981
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
982 983 984 985
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

986
/*
P
Paul E. McKenney 已提交
987
 * Because preemptible RCU does not exist, we never have to check for
988 989 990 991 992 993
 * tasks blocked within RCU read-side critical sections.
 */
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}

994
/*
P
Paul E. McKenney 已提交
995
 * Because preemptible RCU does not exist, we never have to check for
996 997
 * tasks blocked within RCU read-side critical sections.
 */
998
static int rcu_print_task_stall(struct rcu_node *rnp)
999
{
1000
	return 0;
1001 1002
}

1003 1004 1005 1006 1007 1008 1009 1010
/*
 * Because preemptible RCU does not exist, there is no need to suppress
 * its CPU stall warnings.
 */
static void rcu_preempt_stall_reset(void)
{
}

1011
/*
P
Paul E. McKenney 已提交
1012
 * Because there is no preemptible RCU, there can be no readers blocked,
1013 1014
 * so there is no need to check for blocked tasks.  So check only for
 * bogus qsmask values.
1015 1016 1017
 */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
1018
	WARN_ON_ONCE(rnp->qsmask);
1019 1020
}

1021 1022
#ifdef CONFIG_HOTPLUG_CPU

1023
/*
P
Paul E. McKenney 已提交
1024
 * Because preemptible RCU does not exist, it never needs to migrate
1025 1026 1027
 * tasks that were blocked within RCU read-side critical sections, and
 * such non-existent tasks cannot possibly have been blocking the current
 * grace period.
1028
 */
1029 1030 1031
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
				     struct rcu_node *rnp,
				     struct rcu_data *rdp)
1032
{
1033
	return 0;
1034 1035
}

1036 1037
#endif /* #ifdef CONFIG_HOTPLUG_CPU */

1038
/*
P
Paul E. McKenney 已提交
1039
 * Because preemptible RCU does not exist, it never needs CPU-offline
1040 1041
 * processing.
 */
1042
static void rcu_preempt_cleanup_dead_cpu(int cpu)
1043 1044 1045
{
}

1046
/*
P
Paul E. McKenney 已提交
1047
 * Because preemptible RCU does not exist, it never has any callbacks
1048 1049
 * to check.
 */
1050
static void rcu_preempt_check_callbacks(int cpu)
1051 1052 1053 1054
{
}

/*
P
Paul E. McKenney 已提交
1055
 * Because preemptible RCU does not exist, it never has any callbacks
1056 1057
 * to process.
 */
1058
static void rcu_preempt_process_callbacks(void)
1059 1060 1061
{
}

1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077
/*
 * Queue an RCU callback for lazy invocation after a grace period.
 * This will likely be later named something like "call_rcu_lazy()",
 * but this change will require some way of tagging the lazy RCU
 * callbacks in the list of pending callbacks.  Until then, this
 * function may only be called from __kfree_rcu().
 *
 * Because there is no preemptible RCU, we use RCU-sched instead.
 */
void kfree_call_rcu(struct rcu_head *head,
		    void (*func)(struct rcu_head *rcu))
{
	__call_rcu(head, func, &rcu_sched_state, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);

1078 1079
/*
 * Wait for an rcu-preempt grace period, but make it happen quickly.
P
Paul E. McKenney 已提交
1080
 * But because preemptible RCU does not exist, map to rcu-sched.
1081 1082 1083 1084 1085 1086 1087
 */
void synchronize_rcu_expedited(void)
{
	synchronize_sched_expedited();
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

1088 1089 1090
#ifdef CONFIG_HOTPLUG_CPU

/*
P
Paul E. McKenney 已提交
1091
 * Because preemptible RCU does not exist, there is never any need to
1092 1093 1094
 * report on tasks preempted in RCU read-side critical sections during
 * expedited RCU grace periods.
 */
1095 1096
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
			       bool wake)
1097 1098 1099 1100 1101
{
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

1102
/*
P
Paul E. McKenney 已提交
1103
 * Because preemptible RCU does not exist, it never has any work to do.
1104 1105 1106 1107 1108 1109 1110
 */
static int rcu_preempt_pending(int cpu)
{
	return 0;
}

/*
1111
 * Because preemptible RCU does not exist, it never has callbacks
1112
 */
1113
static int rcu_preempt_cpu_has_callbacks(int cpu)
1114 1115 1116 1117
{
	return 0;
}

1118
/*
P
Paul E. McKenney 已提交
1119
 * Because preemptible RCU does not exist, rcu_barrier() is just
1120 1121 1122 1123 1124 1125 1126 1127
 * another name for rcu_barrier_sched().
 */
void rcu_barrier(void)
{
	rcu_barrier_sched();
}
EXPORT_SYMBOL_GPL(rcu_barrier);

1128
/*
P
Paul E. McKenney 已提交
1129
 * Because preemptible RCU does not exist, there is no per-CPU
1130 1131 1132 1133 1134 1135
 * data to initialize.
 */
static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
{
}

1136
/*
1137
 * Because there is no preemptible RCU, there is no cleanup to do.
1138
 */
1139
static void rcu_preempt_cleanup_dying_cpu(void)
1140 1141 1142
{
}

1143
/*
P
Paul E. McKenney 已提交
1144
 * Because preemptible RCU does not exist, it need not be initialized.
1145 1146 1147 1148 1149
 */
static void __init __rcu_init_preempt(void)
{
}

1150
#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1151

1152 1153 1154 1155
#ifdef CONFIG_RCU_BOOST

#include "rtmutex_common.h"

1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168
#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 &&
1169
		 ULONG_CMP_LT(jiffies, rnp->boost_time))
1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182
		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 */

1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217
/*
 * 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);

	/*
	 * 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.
	 */
1218
	if (rnp->exp_tasks != NULL) {
1219
		tb = rnp->exp_tasks;
1220 1221
		rnp->n_exp_boosts++;
	} else {
1222
		tb = rnp->boost_tasks;
1223 1224 1225
		rnp->n_normal_boosts++;
	}
	rnp->n_tasks_boosted++;
1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249

	/*
	 * 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. */

1250 1251
	return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
	       ACCESS_ONCE(rnp->boost_tasks) != NULL;
1252 1253 1254 1255 1256 1257 1258 1259 1260 1261
}

/*
 * Timer handler to initiate waking up of boost kthreads that
 * have yielded the CPU due to excessive numbers of tasks to
 * boost.  We wake up the per-rcu_node kthread, which in turn
 * will wake up the booster kthread.
 */
static void rcu_boost_kthread_timer(unsigned long arg)
{
1262
	invoke_rcu_node_kthread((struct rcu_node *)arg);
1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274
}

/*
 * 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;

1275
	trace_rcu_utilization("Start boost kthread@init");
1276
	for (;;) {
1277
		rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1278
		trace_rcu_utilization("End boost kthread@rcu_wait");
1279
		rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1280
		trace_rcu_utilization("Start boost kthread@rcu_wait");
1281
		rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1282 1283 1284 1285 1286 1287
		more2boost = rcu_boost(rnp);
		if (more2boost)
			spincnt++;
		else
			spincnt = 0;
		if (spincnt > 10) {
1288
			trace_rcu_utilization("End boost kthread@rcu_yield");
1289
			rcu_yield(rcu_boost_kthread_timer, (unsigned long)rnp);
1290
			trace_rcu_utilization("Start boost kthread@rcu_yield");
1291 1292 1293
			spincnt = 0;
		}
	}
1294
	/* NOTREACHED */
1295
	trace_rcu_utilization("End boost kthread@notreached");
1296 1297 1298 1299 1300 1301 1302 1303 1304
	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.
 *
1305 1306 1307
 * The caller must hold rnp->lock, which this function releases,
 * but irqs remain disabled.  The ->boost_kthread_task is immortal,
 * so we don't need to worry about it going away.
1308
 */
1309
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1310 1311 1312
{
	struct task_struct *t;

1313 1314
	if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
		rnp->n_balk_exp_gp_tasks++;
1315
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1316
		return;
1317
	}
1318 1319 1320 1321 1322 1323 1324
	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;
1325
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1326 1327 1328
		t = rnp->boost_kthread_task;
		if (t != NULL)
			wake_up_process(t);
1329
	} else {
1330
		rcu_initiate_boost_trace(rnp);
1331 1332
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
	}
1333 1334
}

1335 1336 1337 1338 1339 1340 1341 1342 1343
/*
 * 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);
1344 1345 1346
	if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
	    current != __this_cpu_read(rcu_cpu_kthread_task))
		wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
1347 1348 1349
	local_irq_restore(flags);
}

1350 1351 1352 1353 1354 1355 1356 1357 1358
/*
 * Is the current CPU running the RCU-callbacks kthread?
 * Caller must have preemption disabled.
 */
static bool rcu_is_callbacks_kthread(void)
{
	return __get_cpu_var(rcu_cpu_kthread_task) == current;
}

1359 1360 1361 1362 1363
/*
 * Set the affinity of the boost kthread.  The CPU-hotplug locks are
 * held, so no one should be messing with the existence of the boost
 * kthread.
 */
1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
					  cpumask_var_t cm)
{
	struct task_struct *t;

	t = rnp->boost_kthread_task;
	if (t != NULL)
		set_cpus_allowed_ptr(rnp->boost_kthread_task, cm);
}

#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)

/*
 * Do priority-boost accounting for the start of a new grace period.
 */
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
	rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
}

/*
 * Create an RCU-boost kthread for the specified node if one does not
 * already exist.  We only create this kthread for preemptible RCU.
 * Returns zero if all is well, a negated errno otherwise.
 */
static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
						 struct rcu_node *rnp,
						 int rnp_index)
{
	unsigned long flags;
	struct sched_param sp;
	struct task_struct *t;

	if (&rcu_preempt_state != rsp)
		return 0;
1399
	rsp->boost = 1;
1400 1401 1402
	if (rnp->boost_kthread_task != NULL)
		return 0;
	t = kthread_create(rcu_boost_kthread, (void *)rnp,
1403
			   "rcub/%d", rnp_index);
1404 1405 1406 1407 1408
	if (IS_ERR(t))
		return PTR_ERR(t);
	raw_spin_lock_irqsave(&rnp->lock, flags);
	rnp->boost_kthread_task = t;
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1409
	sp.sched_priority = RCU_BOOST_PRIO;
1410
	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1411
	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1412 1413 1414
	return 0;
}

1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503
#ifdef CONFIG_HOTPLUG_CPU

/*
 * Stop the RCU's per-CPU kthread when its CPU goes offline,.
 */
static void rcu_stop_cpu_kthread(int cpu)
{
	struct task_struct *t;

	/* Stop the CPU's kthread. */
	t = per_cpu(rcu_cpu_kthread_task, cpu);
	if (t != NULL) {
		per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
		kthread_stop(t);
	}
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

static void rcu_kthread_do_work(void)
{
	rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
	rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
	rcu_preempt_do_callbacks();
}

/*
 * Wake up the specified per-rcu_node-structure kthread.
 * Because the per-rcu_node kthreads are immortal, we don't need
 * to do anything to keep them alive.
 */
static void invoke_rcu_node_kthread(struct rcu_node *rnp)
{
	struct task_struct *t;

	t = rnp->node_kthread_task;
	if (t != NULL)
		wake_up_process(t);
}

/*
 * Set the specified CPU's kthread to run RT or not, as specified by
 * the to_rt argument.  The CPU-hotplug locks are held, so the task
 * is not going away.
 */
static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
{
	int policy;
	struct sched_param sp;
	struct task_struct *t;

	t = per_cpu(rcu_cpu_kthread_task, cpu);
	if (t == NULL)
		return;
	if (to_rt) {
		policy = SCHED_FIFO;
		sp.sched_priority = RCU_KTHREAD_PRIO;
	} else {
		policy = SCHED_NORMAL;
		sp.sched_priority = 0;
	}
	sched_setscheduler_nocheck(t, policy, &sp);
}

/*
 * Timer handler to initiate the waking up of per-CPU kthreads that
 * have yielded the CPU due to excess numbers of RCU callbacks.
 * We wake up the per-rcu_node kthread, which in turn will wake up
 * the booster kthread.
 */
static void rcu_cpu_kthread_timer(unsigned long arg)
{
	struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg);
	struct rcu_node *rnp = rdp->mynode;

	atomic_or(rdp->grpmask, &rnp->wakemask);
	invoke_rcu_node_kthread(rnp);
}

/*
 * Drop to non-real-time priority and yield, but only after posting a
 * timer that will cause us to regain our real-time priority if we
 * remain preempted.  Either way, we restore our real-time priority
 * before returning.
 */
static void rcu_yield(void (*f)(unsigned long), unsigned long arg)
{
	struct sched_param sp;
	struct timer_list yield_timer;
1504
	int prio = current->rt_priority;
1505 1506 1507 1508 1509 1510 1511

	setup_timer_on_stack(&yield_timer, f, arg);
	mod_timer(&yield_timer, jiffies + 2);
	sp.sched_priority = 0;
	sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
	set_user_nice(current, 19);
	schedule();
1512 1513
	set_user_nice(current, 0);
	sp.sched_priority = prio;
1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550
	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
	del_timer(&yield_timer);
}

/*
 * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU.
 * This can happen while the corresponding CPU is either coming online
 * or going offline.  We cannot wait until the CPU is fully online
 * before starting the kthread, because the various notifier functions
 * can wait for RCU grace periods.  So we park rcu_cpu_kthread() until
 * the corresponding CPU is online.
 *
 * Return 1 if the kthread needs to stop, 0 otherwise.
 *
 * Caller must disable bh.  This function can momentarily enable it.
 */
static int rcu_cpu_kthread_should_stop(int cpu)
{
	while (cpu_is_offline(cpu) ||
	       !cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)) ||
	       smp_processor_id() != cpu) {
		if (kthread_should_stop())
			return 1;
		per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
		per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id();
		local_bh_enable();
		schedule_timeout_uninterruptible(1);
		if (!cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)))
			set_cpus_allowed_ptr(current, cpumask_of(cpu));
		local_bh_disable();
	}
	per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
	return 0;
}

/*
 * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
1551 1552
 * RCU softirq used in flavors and configurations of RCU that do not
 * support RCU priority boosting.
1553 1554 1555 1556 1557 1558 1559 1560 1561 1562
 */
static int rcu_cpu_kthread(void *arg)
{
	int cpu = (int)(long)arg;
	unsigned long flags;
	int spincnt = 0;
	unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
	char work;
	char *workp = &per_cpu(rcu_cpu_has_work, cpu);

1563
	trace_rcu_utilization("Start CPU kthread@init");
1564 1565
	for (;;) {
		*statusp = RCU_KTHREAD_WAITING;
1566
		trace_rcu_utilization("End CPU kthread@rcu_wait");
1567
		rcu_wait(*workp != 0 || kthread_should_stop());
1568
		trace_rcu_utilization("Start CPU kthread@rcu_wait");
1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588
		local_bh_disable();
		if (rcu_cpu_kthread_should_stop(cpu)) {
			local_bh_enable();
			break;
		}
		*statusp = RCU_KTHREAD_RUNNING;
		per_cpu(rcu_cpu_kthread_loops, cpu)++;
		local_irq_save(flags);
		work = *workp;
		*workp = 0;
		local_irq_restore(flags);
		if (work)
			rcu_kthread_do_work();
		local_bh_enable();
		if (*workp != 0)
			spincnt++;
		else
			spincnt = 0;
		if (spincnt > 10) {
			*statusp = RCU_KTHREAD_YIELDING;
1589
			trace_rcu_utilization("End CPU kthread@rcu_yield");
1590
			rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu);
1591
			trace_rcu_utilization("Start CPU kthread@rcu_yield");
1592 1593 1594 1595
			spincnt = 0;
		}
	}
	*statusp = RCU_KTHREAD_STOPPED;
1596
	trace_rcu_utilization("End CPU kthread@term");
1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625
	return 0;
}

/*
 * Spawn a per-CPU kthread, setting up affinity and priority.
 * Because the CPU hotplug lock is held, no other CPU will be attempting
 * to manipulate rcu_cpu_kthread_task.  There might be another CPU
 * attempting to access it during boot, but the locking in kthread_bind()
 * will enforce sufficient ordering.
 *
 * Please note that we cannot simply refuse to wake up the per-CPU
 * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state,
 * which can result in softlockup complaints if the task ends up being
 * idle for more than a couple of minutes.
 *
 * However, please note also that we cannot bind the per-CPU kthread to its
 * CPU until that CPU is fully online.  We also cannot wait until the
 * CPU is fully online before we create its per-CPU kthread, as this would
 * deadlock the system when CPU notifiers tried waiting for grace
 * periods.  So we bind the per-CPU kthread to its CPU only if the CPU
 * is online.  If its CPU is not yet fully online, then the code in
 * rcu_cpu_kthread() will wait until it is fully online, and then do
 * the binding.
 */
static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
{
	struct sched_param sp;
	struct task_struct *t;

1626
	if (!rcu_scheduler_fully_active ||
1627 1628
	    per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
		return 0;
E
Eric Dumazet 已提交
1629 1630 1631
	t = kthread_create_on_node(rcu_cpu_kthread,
				   (void *)(long)cpu,
				   cpu_to_node(cpu),
1632
				   "rcuc/%d", cpu);
1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735
	if (IS_ERR(t))
		return PTR_ERR(t);
	if (cpu_online(cpu))
		kthread_bind(t, cpu);
	per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
	WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
	sp.sched_priority = RCU_KTHREAD_PRIO;
	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
	per_cpu(rcu_cpu_kthread_task, cpu) = t;
	wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */
	return 0;
}

/*
 * Per-rcu_node kthread, which is in charge of waking up the per-CPU
 * kthreads when needed.  We ignore requests to wake up kthreads
 * for offline CPUs, which is OK because force_quiescent_state()
 * takes care of this case.
 */
static int rcu_node_kthread(void *arg)
{
	int cpu;
	unsigned long flags;
	unsigned long mask;
	struct rcu_node *rnp = (struct rcu_node *)arg;
	struct sched_param sp;
	struct task_struct *t;

	for (;;) {
		rnp->node_kthread_status = RCU_KTHREAD_WAITING;
		rcu_wait(atomic_read(&rnp->wakemask) != 0);
		rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
		raw_spin_lock_irqsave(&rnp->lock, flags);
		mask = atomic_xchg(&rnp->wakemask, 0);
		rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
		for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
			if ((mask & 0x1) == 0)
				continue;
			preempt_disable();
			t = per_cpu(rcu_cpu_kthread_task, cpu);
			if (!cpu_online(cpu) || t == NULL) {
				preempt_enable();
				continue;
			}
			per_cpu(rcu_cpu_has_work, cpu) = 1;
			sp.sched_priority = RCU_KTHREAD_PRIO;
			sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
			preempt_enable();
		}
	}
	/* NOTREACHED */
	rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
	return 0;
}

/*
 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
 * served by the rcu_node in question.  The CPU hotplug lock is still
 * held, so the value of rnp->qsmaskinit will be stable.
 *
 * We don't include outgoingcpu in the affinity set, use -1 if there is
 * no outgoing CPU.  If there are no CPUs left in the affinity set,
 * this function allows the kthread to execute on any CPU.
 */
static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
{
	cpumask_var_t cm;
	int cpu;
	unsigned long mask = rnp->qsmaskinit;

	if (rnp->node_kthread_task == NULL)
		return;
	if (!alloc_cpumask_var(&cm, GFP_KERNEL))
		return;
	cpumask_clear(cm);
	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);
	}
	set_cpus_allowed_ptr(rnp->node_kthread_task, cm);
	rcu_boost_kthread_setaffinity(rnp, cm);
	free_cpumask_var(cm);
}

/*
 * Spawn a per-rcu_node kthread, setting priority and affinity.
 * Called during boot before online/offline can happen, or, if
 * during runtime, with the main CPU-hotplug locks held.  So only
 * one of these can be executing at a time.
 */
static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
						struct rcu_node *rnp)
{
	unsigned long flags;
	int rnp_index = rnp - &rsp->node[0];
	struct sched_param sp;
	struct task_struct *t;

1736
	if (!rcu_scheduler_fully_active ||
1737 1738 1739 1740
	    rnp->qsmaskinit == 0)
		return 0;
	if (rnp->node_kthread_task == NULL) {
		t = kthread_create(rcu_node_kthread, (void *)rnp,
1741
				   "rcun/%d", rnp_index);
1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761
		if (IS_ERR(t))
			return PTR_ERR(t);
		raw_spin_lock_irqsave(&rnp->lock, flags);
		rnp->node_kthread_task = t;
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		sp.sched_priority = 99;
		sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
		wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
	}
	return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);
}

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

1762
	rcu_scheduler_fully_active = 1;
1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783
	for_each_possible_cpu(cpu) {
		per_cpu(rcu_cpu_has_work, cpu) = 0;
		if (cpu_online(cpu))
			(void)rcu_spawn_one_cpu_kthread(cpu);
	}
	rnp = rcu_get_root(rcu_state);
	(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
	if (NUM_RCU_NODES > 1) {
		rcu_for_each_leaf_node(rcu_state, rnp)
			(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
	}
	return 0;
}
early_initcall(rcu_spawn_kthreads);

static void __cpuinit rcu_prepare_kthreads(int cpu)
{
	struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
	struct rcu_node *rnp = rdp->mynode;

	/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1784
	if (rcu_scheduler_fully_active) {
1785 1786 1787 1788 1789 1790
		(void)rcu_spawn_one_cpu_kthread(cpu);
		if (rnp->node_kthread_task == NULL)
			(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
	}
}

1791 1792
#else /* #ifdef CONFIG_RCU_BOOST */

1793
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1794
{
1795
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1796 1797
}

1798
static void invoke_rcu_callbacks_kthread(void)
1799
{
1800
	WARN_ON_ONCE(1);
1801 1802
}

1803 1804 1805 1806 1807
static bool rcu_is_callbacks_kthread(void)
{
	return false;
}

1808 1809 1810 1811
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
}

1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827
#ifdef CONFIG_HOTPLUG_CPU

static void rcu_stop_cpu_kthread(int cpu)
{
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
{
}

static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
{
}

1828 1829 1830 1831 1832 1833 1834
static int __init rcu_scheduler_really_started(void)
{
	rcu_scheduler_fully_active = 1;
	return 0;
}
early_initcall(rcu_scheduler_really_started);

1835 1836 1837 1838
static void __cpuinit rcu_prepare_kthreads(int cpu)
{
}

1839 1840
#endif /* #else #ifdef CONFIG_RCU_BOOST */

1841 1842 1843 1844 1845 1846 1847 1848
#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.
 *
1849 1850
 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
 * any flavor of RCU.
1851
 */
1852
int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1853
{
1854
	*delta_jiffies = ULONG_MAX;
1855 1856 1857
	return rcu_cpu_has_callbacks(cpu);
}

1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872
/*
 * Because we do not have RCU_FAST_NO_HZ, don't bother initializing for it.
 */
static void rcu_prepare_for_idle_init(int cpu)
{
}

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

1873
/*
1874
 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1875 1876 1877 1878 1879 1880
 * is nothing.
 */
static void rcu_prepare_for_idle(int cpu)
{
}

1881 1882 1883 1884 1885 1886 1887 1888
/*
 * 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)
{
}

1889 1890
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */

1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915
/*
 * 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_FLUSHES gives the maximum number of times that we will attempt
 *	to satisfy RCU.  Beyond this point, it is better to incur a periodic
 *	scheduling-clock interrupt than to loop through the state machine
 *	at full power.
 * RCU_IDLE_OPT_FLUSHES gives the number of RCU_IDLE_FLUSHES that are
 *	optional if RCU does not need anything immediately from this
 *	CPU, even if this CPU still has RCU callbacks queued.  The first
 *	times through the state machine are mandatory: we need to give
 *	the state machine a chance to communicate a quiescent state
 *	to the RCU core.
 * 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!
1916 1917 1918
 * 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.
1919 1920 1921 1922 1923 1924 1925
 *
 * The values below work well in practice.  If future workloads require
 * adjustment, they can be converted into kernel config parameters, though
 * making the state machine smarter might be a better option.
 */
#define RCU_IDLE_FLUSHES 5		/* Number of dyntick-idle tries. */
#define RCU_IDLE_OPT_FLUSHES 3		/* Optional dyntick-idle tries. */
1926
#define RCU_IDLE_GP_DELAY 6		/* Roughly one grace period. */
1927
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ)	/* Roughly six seconds. */
1928

1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970
/*
 * Does the specified flavor of RCU have non-lazy callbacks pending on
 * the specified CPU?  Both RCU flavor and CPU are specified by the
 * rcu_data structure.
 */
static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp)
{
	return rdp->qlen != rdp->qlen_lazy;
}

#ifdef CONFIG_TREE_PREEMPT_RCU

/*
 * Are there non-lazy RCU-preempt callbacks?  (There cannot be if there
 * is no RCU-preempt in the kernel.)
 */
static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
{
	struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);

	return __rcu_cpu_has_nonlazy_callbacks(rdp);
}

#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */

static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
{
	return 0;
}

#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */

/*
 * Does any flavor of RCU have non-lazy callbacks on the specified CPU?
 */
static bool rcu_cpu_has_nonlazy_callbacks(int cpu)
{
	return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) ||
	       __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) ||
	       rcu_preempt_cpu_has_nonlazy_callbacks(cpu);
}

1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 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
/*
 * Allow the CPU to enter dyntick-idle mode if either: (1) There are no
 * callbacks on this CPU, (2) this CPU has not yet attempted to enter
 * dyntick-idle mode, or (3) this CPU is in the process of attempting to
 * enter dyntick-idle mode.  Otherwise, if we have recently tried and failed
 * to enter dyntick-idle mode, we refuse to try to enter it.  After all,
 * it is better to incur scheduling-clock interrupts than to spin
 * continuously for the same time duration!
 *
 * The delta_jiffies argument is used to store the time when RCU is
 * going to need the CPU again if it still has callbacks.  The reason
 * for this is that rcu_prepare_for_idle() might need to post a timer,
 * but if so, it will do so after tick_nohz_stop_sched_tick() has set
 * the wakeup time for this CPU.  This means that RCU's timer can be
 * delayed until the wakeup time, which defeats the purpose of posting
 * a timer.
 */
int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
{
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);

	/* Flag a new idle sojourn to the idle-entry state machine. */
	rdtp->idle_first_pass = 1;
	/* If no callbacks, RCU doesn't need the CPU. */
	if (!rcu_cpu_has_callbacks(cpu)) {
		*delta_jiffies = ULONG_MAX;
		return 0;
	}
	if (rdtp->dyntick_holdoff == jiffies) {
		/* RCU recently tried and failed, so don't try again. */
		*delta_jiffies = 1;
		return 1;
	}
	/* Set up for the possibility that RCU will post a timer. */
	if (rcu_cpu_has_nonlazy_callbacks(cpu))
		*delta_jiffies = RCU_IDLE_GP_DELAY;
	else
		*delta_jiffies = RCU_IDLE_LAZY_GP_DELAY;
	return 0;
}

2012 2013 2014 2015 2016 2017 2018 2019 2020
/*
 * Handler for smp_call_function_single().  The only point of this
 * handler is to wake the CPU up, so the handler does only tracing.
 */
void rcu_idle_demigrate(void *unused)
{
	trace_rcu_prep_idle("Demigrate");
}

2021 2022 2023 2024 2025 2026
/*
 * Timer handler used to force CPU to start pushing its remaining RCU
 * callbacks in the case where it entered dyntick-idle mode with callbacks
 * pending.  The hander doesn't really need to do anything because the
 * real work is done upon re-entry to idle, or by the next scheduling-clock
 * interrupt should idle not be re-entered.
2027 2028 2029 2030
 *
 * One special case: the timer gets migrated without awakening the CPU
 * on which the timer was scheduled on.  In this case, we must wake up
 * that CPU.  We do so with smp_call_function_single().
2031
 */
2032
static void rcu_idle_gp_timer_func(unsigned long cpu_in)
2033
{
2034 2035
	int cpu = (int)cpu_in;

2036
	trace_rcu_prep_idle("Timer");
2037 2038 2039 2040
	if (cpu != smp_processor_id())
		smp_call_function_single(cpu, rcu_idle_demigrate, NULL, 0);
	else
		WARN_ON_ONCE(1); /* Getting here can hang the system... */
2041 2042 2043 2044 2045 2046 2047
}

/*
 * Initialize the timer used to pull CPUs out of dyntick-idle mode.
 */
static void rcu_prepare_for_idle_init(int cpu)
{
2048 2049 2050 2051 2052 2053
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);

	rdtp->dyntick_holdoff = jiffies - 1;
	setup_timer(&rdtp->idle_gp_timer, rcu_idle_gp_timer_func, cpu);
	rdtp->idle_gp_timer_expires = jiffies - 1;
	rdtp->idle_first_pass = 1;
2054 2055 2056 2057
}

/*
 * Clean up for exit from idle.  Because we are exiting from idle, there
2058
 * is no longer any point to ->idle_gp_timer, so cancel it.  This will
2059 2060 2061 2062
 * do nothing if this timer is not active, so just cancel it unconditionally.
 */
static void rcu_cleanup_after_idle(int cpu)
{
2063 2064 2065
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);

	del_timer(&rdtp->idle_gp_timer);
2066
	trace_rcu_prep_idle("Cleanup after idle");
2067 2068
}

2069 2070 2071 2072
/*
 * Check to see if any RCU-related work can be done by the current CPU,
 * and if so, schedule a softirq to get it done.  This function is part
 * of the RCU implementation; it is -not- an exported member of the RCU API.
2073
 *
2074 2075 2076 2077 2078 2079
 * The idea is for the current CPU to clear out all work required by the
 * RCU core for the current grace period, so that this CPU can be permitted
 * to enter dyntick-idle mode.  In some cases, it will need to be awakened
 * at the end of the grace period by whatever CPU ends the grace period.
 * This allows CPUs to go dyntick-idle more quickly, and to reduce the
 * number of wakeups by a modest integer factor.
2080 2081 2082
 *
 * Because it is not legal to invoke rcu_process_callbacks() with irqs
 * disabled, we do one pass of force_quiescent_state(), then do a
2083
 * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked
2084
 * later.  The ->dyntick_drain field controls the sequencing.
2085 2086
 *
 * The caller must have disabled interrupts.
2087
 */
2088
static void rcu_prepare_for_idle(int cpu)
2089
{
2090
	struct timer_list *tp;
2091
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
2092

2093 2094 2095 2096 2097
	/*
	 * If this is an idle re-entry, for example, due to use of
	 * RCU_NONIDLE() or the new idle-loop tracing API within the idle
	 * loop, then don't take any state-machine actions, unless the
	 * momentary exit from idle queued additional non-lazy callbacks.
2098
	 * Instead, repost the ->idle_gp_timer if this CPU has callbacks
2099 2100
	 * pending.
	 */
2101 2102
	if (!rdtp->idle_first_pass &&
	    (rdtp->nonlazy_posted == rdtp->nonlazy_posted_snap)) {
2103
		if (rcu_cpu_has_callbacks(cpu)) {
2104 2105
			tp = &rdtp->idle_gp_timer;
			mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
2106
		}
2107 2108
		return;
	}
2109 2110
	rdtp->idle_first_pass = 0;
	rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted - 1;
2111

2112
	/*
2113 2114
	 * If there are no callbacks on this CPU, enter dyntick-idle mode.
	 * Also reset state to avoid prejudicing later attempts.
2115
	 */
2116
	if (!rcu_cpu_has_callbacks(cpu)) {
2117 2118
		rdtp->dyntick_holdoff = jiffies - 1;
		rdtp->dyntick_drain = 0;
2119
		trace_rcu_prep_idle("No callbacks");
2120
		return;
2121
	}
2122 2123 2124 2125 2126

	/*
	 * If in holdoff mode, just return.  We will presumably have
	 * refrained from disabling the scheduling-clock tick.
	 */
2127
	if (rdtp->dyntick_holdoff == jiffies) {
2128
		trace_rcu_prep_idle("In holdoff");
2129
		return;
2130
	}
2131

2132 2133
	/* Check and update the ->dyntick_drain sequencing. */
	if (rdtp->dyntick_drain <= 0) {
2134
		/* First time through, initialize the counter. */
2135 2136
		rdtp->dyntick_drain = RCU_IDLE_FLUSHES;
	} else if (rdtp->dyntick_drain <= RCU_IDLE_OPT_FLUSHES &&
2137 2138
		   !rcu_pending(cpu) &&
		   !local_softirq_pending()) {
2139
		/* Can we go dyntick-idle despite still having callbacks? */
2140 2141
		rdtp->dyntick_drain = 0;
		rdtp->dyntick_holdoff = jiffies;
2142 2143
		if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
			trace_rcu_prep_idle("Dyntick with callbacks");
2144
			rdtp->idle_gp_timer_expires =
2145
					   jiffies + RCU_IDLE_GP_DELAY;
2146
		} else {
2147
			rdtp->idle_gp_timer_expires =
2148
					   jiffies + RCU_IDLE_LAZY_GP_DELAY;
2149 2150
			trace_rcu_prep_idle("Dyntick with lazy callbacks");
		}
2151 2152 2153
		tp = &rdtp->idle_gp_timer;
		mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
		rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
2154
		return; /* Nothing more to do immediately. */
2155
	} else if (--(rdtp->dyntick_drain) <= 0) {
2156
		/* We have hit the limit, so time to give up. */
2157
		rdtp->dyntick_holdoff = jiffies;
2158
		trace_rcu_prep_idle("Begin holdoff");
2159 2160
		invoke_rcu_core();  /* Force the CPU out of dyntick-idle. */
		return;
2161 2162
	}

2163 2164 2165 2166 2167 2168 2169 2170 2171 2172
	/*
	 * Do one step of pushing the remaining RCU callbacks through
	 * the RCU core state machine.
	 */
#ifdef CONFIG_TREE_PREEMPT_RCU
	if (per_cpu(rcu_preempt_data, cpu).nxtlist) {
		rcu_preempt_qs(cpu);
		force_quiescent_state(&rcu_preempt_state, 0);
	}
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
2173 2174 2175 2176 2177 2178 2179
	if (per_cpu(rcu_sched_data, cpu).nxtlist) {
		rcu_sched_qs(cpu);
		force_quiescent_state(&rcu_sched_state, 0);
	}
	if (per_cpu(rcu_bh_data, cpu).nxtlist) {
		rcu_bh_qs(cpu);
		force_quiescent_state(&rcu_bh_state, 0);
2180 2181
	}

2182 2183 2184 2185
	/*
	 * If RCU callbacks are still pending, RCU still needs this CPU.
	 * So try forcing the callbacks through the grace period.
	 */
2186
	if (rcu_cpu_has_callbacks(cpu)) {
2187
		trace_rcu_prep_idle("More callbacks");
2188
		invoke_rcu_core();
2189
	} else
2190
		trace_rcu_prep_idle("Callbacks drained");
2191 2192
}

2193
/*
2194 2195 2196 2197 2198 2199
 * 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().
2200 2201 2202
 */
static void rcu_idle_count_callbacks_posted(void)
{
2203
	__this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
2204 2205
}

2206
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
2207 2208 2209 2210 2211 2212 2213

#ifdef CONFIG_RCU_CPU_STALL_INFO

#ifdef CONFIG_RCU_FAST_NO_HZ

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
2214 2215
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
	struct timer_list *tltp = &rdtp->idle_gp_timer;
2216

2217
	sprintf(cp, "drain=%d %c timer=%lu",
2218 2219
		rdtp->dyntick_drain,
		rdtp->dyntick_holdoff == jiffies ? 'H' : '.',
2220
		timer_pending(tltp) ? tltp->expires - jiffies : -1);
2221 2222 2223 2224 2225 2226 2227 2228 2229 2230 2231 2232 2233 2234 2235 2236 2237 2238 2239 2240 2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255 2256 2257 2258 2259 2260 2261 2262 2263 2264 2265 2266 2267 2268 2269 2270 2271 2272 2273 2274 2275 2276 2277 2278 2279 2280 2281 2282 2283 2284 2285 2286 2287 2288 2289 2290 2291 2292 2293 2294 2295 2296 2297 2298 2299 2300 2301 2302 2303 2304 2305 2306 2307 2308 2309 2310 2311 2312 2313 2314 2315 2316 2317 2318 2319
}

#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
}

#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */

/* Initiate the stall-info list. */
static void print_cpu_stall_info_begin(void)
{
	printk(KERN_CONT "\n");
}

/*
 * Print out diagnostic information for the specified stalled CPU.
 *
 * If the specified CPU is aware of the current RCU grace period
 * (flavor specified by rsp), then print the number of scheduling
 * clock interrupts the CPU has taken during the time that it has
 * been aware.  Otherwise, print the number of RCU grace periods
 * that this CPU is ignorant of, for example, "1" if the CPU was
 * aware of the previous grace period.
 *
 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
 */
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
	char fast_no_hz[72];
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
	struct rcu_dynticks *rdtp = rdp->dynticks;
	char *ticks_title;
	unsigned long ticks_value;

	if (rsp->gpnum == rdp->gpnum) {
		ticks_title = "ticks this GP";
		ticks_value = rdp->ticks_this_gp;
	} else {
		ticks_title = "GPs behind";
		ticks_value = rsp->gpnum - rdp->gpnum;
	}
	print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
	printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d %s\n",
	       cpu, ticks_value, ticks_title,
	       atomic_read(&rdtp->dynticks) & 0xfff,
	       rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
	       fast_no_hz);
}

/* Terminate the stall-info list. */
static void print_cpu_stall_info_end(void)
{
	printk(KERN_ERR "\t");
}

/* Zero ->ticks_this_gp for all flavors of RCU. */
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
	rdp->ticks_this_gp = 0;
}

/* Increment ->ticks_this_gp for all flavors of RCU. */
static void increment_cpu_stall_ticks(void)
{
	__get_cpu_var(rcu_sched_data).ticks_this_gp++;
	__get_cpu_var(rcu_bh_data).ticks_this_gp++;
#ifdef CONFIG_TREE_PREEMPT_RCU
	__get_cpu_var(rcu_preempt_data).ticks_this_gp++;
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

static void print_cpu_stall_info_begin(void)
{
	printk(KERN_CONT " {");
}

static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
	printk(KERN_CONT " %d", cpu);
}

static void print_cpu_stall_info_end(void)
{
	printk(KERN_CONT "} ");
}

static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
}

static void increment_cpu_stall_ticks(void)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */