rcu: Add documentation for raw SRCU read-side primitives

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / kernel / rcutiny.c

/*
 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
 *
 * 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 IBM Corporation, 2008
 *
 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 *
 * For detailed explanation of Read-Copy Update mechanism see -
 *		Documentation/RCU
 */
#include <linux/completion.h>
#include <linux/interrupt.h>
#include <linux/notifier.h>
#include <linux/rcupdate.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/init.h>
#include <linux/time.h>
#include <linux/cpu.h>
#include <linux/prefetch.h>

#ifdef CONFIG_RCU_TRACE
#include <trace/events/rcu.h>
#endif /* #else #ifdef CONFIG_RCU_TRACE */

#include "rcu.h"

/* Forward declarations for rcutiny_plugin.h. */
struct rcu_ctrlblk;
static void invoke_rcu_callbacks(void);
static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
static void rcu_process_callbacks(struct softirq_action *unused);
static void __call_rcu(struct rcu_head *head,
		       void (*func)(struct rcu_head *rcu),
		       struct rcu_ctrlblk *rcp);

#include "rcutiny_plugin.h"

static long long rcu_dynticks_nesting = LLONG_MAX / 2;

/* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
static void rcu_idle_enter_common(void)
{
	if (rcu_dynticks_nesting) {
		RCU_TRACE(trace_rcu_dyntick("--=", rcu_dynticks_nesting));
		return;
	}
	RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting));
	if (!idle_cpu(smp_processor_id())) {
		WARN_ON_ONCE(1);	/* must be idle task! */
		RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
					    rcu_dynticks_nesting));
		ftrace_dump(DUMP_ALL);
	}
	rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
}

/*
 * Enter idle, which is an extended quiescent state if we have fully
 * entered that mode (i.e., if the new value of dynticks_nesting is zero).
 */
void rcu_idle_enter(void)
{
	unsigned long flags;

	local_irq_save(flags);
	rcu_dynticks_nesting = 0;
	rcu_idle_enter_common();
	local_irq_restore(flags);
}

/*
 * Exit an interrupt handler towards idle.
 */
void rcu_irq_exit(void)
{
	unsigned long flags;

	local_irq_save(flags);
	rcu_dynticks_nesting--;
	WARN_ON_ONCE(rcu_dynticks_nesting < 0);
	rcu_idle_enter_common();
	local_irq_restore(flags);
}

/* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
static void rcu_idle_exit_common(long long oldval)
{
	if (oldval) {
		RCU_TRACE(trace_rcu_dyntick("++=", rcu_dynticks_nesting));
		return;
	}
	RCU_TRACE(trace_rcu_dyntick("End", oldval));
	if (!idle_cpu(smp_processor_id())) {
		WARN_ON_ONCE(1);	/* must be idle task! */
		RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
			  oldval));
		ftrace_dump(DUMP_ALL);
	}
}

/*
 * Exit idle, so that we are no longer in an extended quiescent state.
 */
void rcu_idle_exit(void)
{
	unsigned long flags;
	long long oldval;

	local_irq_save(flags);
	oldval = rcu_dynticks_nesting;
	WARN_ON_ONCE(oldval != 0);
	rcu_dynticks_nesting = LLONG_MAX / 2;
	rcu_idle_exit_common(oldval);
	local_irq_restore(flags);
}

/*
 * Enter an interrupt handler, moving away from idle.
 */
void rcu_irq_enter(void)
{
	unsigned long flags;
	long long oldval;

	local_irq_save(flags);
	oldval = rcu_dynticks_nesting;
	rcu_dynticks_nesting++;
	WARN_ON_ONCE(rcu_dynticks_nesting == 0);
	rcu_idle_exit_common(oldval);
	local_irq_restore(flags);
}

#ifdef CONFIG_PROVE_RCU

/*
 * Test whether RCU thinks that the current CPU is idle.
 */
int rcu_is_cpu_idle(void)
{
	return !rcu_dynticks_nesting;
}
EXPORT_SYMBOL(rcu_is_cpu_idle);

#endif /* #ifdef CONFIG_PROVE_RCU */

/*
 * Test whether the current CPU was interrupted from idle.  Nested
 * interrupts don't count, we must be running at the first interrupt
 * level.
 */
int rcu_is_cpu_rrupt_from_idle(void)
{
	return rcu_dynticks_nesting <= 0;
}

/*
 * Helper function for rcu_sched_qs() and rcu_bh_qs().
 * Also irqs are disabled to avoid confusion due to interrupt handlers
 * invoking call_rcu().
 */
static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
{
	if (rcp->rcucblist != NULL &&
	    rcp->donetail != rcp->curtail) {
		rcp->donetail = rcp->curtail;
		return 1;
	}

	return 0;
}

/*
 * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
 * are at it, given that any rcu quiescent state is also an rcu_bh
 * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
 */
void rcu_sched_qs(int cpu)
{
	unsigned long flags;

	local_irq_save(flags);
	if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
	    rcu_qsctr_help(&rcu_bh_ctrlblk))
		invoke_rcu_callbacks();
	local_irq_restore(flags);
}

/*
 * Record an rcu_bh quiescent state.
 */
void rcu_bh_qs(int cpu)
{
	unsigned long flags;

	local_irq_save(flags);
	if (rcu_qsctr_help(&rcu_bh_ctrlblk))
		invoke_rcu_callbacks();
	local_irq_restore(flags);
}

/*
 * Check to see if the scheduling-clock interrupt came from an extended
 * quiescent state, and, if so, tell RCU about it.  This function must
 * be called from hardirq context.  It is normally called from the
 * scheduling-clock interrupt.
 */
void rcu_check_callbacks(int cpu, int user)
{
	if (user || rcu_is_cpu_rrupt_from_idle())
		rcu_sched_qs(cpu);
	else if (!in_softirq())
		rcu_bh_qs(cpu);
	rcu_preempt_check_callbacks();
}

/*
 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
 * whose grace period has elapsed.
 */
static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
{
	char *rn = NULL;
	struct rcu_head *next, *list;
	unsigned long flags;
	RCU_TRACE(int cb_count = 0);

	/* If no RCU callbacks ready to invoke, just return. */
	if (&rcp->rcucblist == rcp->donetail) {
		RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
		RCU_TRACE(trace_rcu_batch_end(rcp->name, 0));
		return;
	}

	/* Move the ready-to-invoke callbacks to a local list. */
	local_irq_save(flags);
	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
	list = rcp->rcucblist;
	rcp->rcucblist = *rcp->donetail;
	*rcp->donetail = NULL;
	if (rcp->curtail == rcp->donetail)
		rcp->curtail = &rcp->rcucblist;
	rcu_preempt_remove_callbacks(rcp);
	rcp->donetail = &rcp->rcucblist;
	local_irq_restore(flags);

	/* Invoke the callbacks on the local list. */
	RCU_TRACE(rn = rcp->name);
	while (list) {
		next = list->next;
		prefetch(next);
		debug_rcu_head_unqueue(list);
		local_bh_disable();
		__rcu_reclaim(rn, list);
		local_bh_enable();
		list = next;
		RCU_TRACE(cb_count++);
	}
	RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
	RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count));
}

static void rcu_process_callbacks(struct softirq_action *unused)
{
	__rcu_process_callbacks(&rcu_sched_ctrlblk);
	__rcu_process_callbacks(&rcu_bh_ctrlblk);
	rcu_preempt_process_callbacks();
}

/*
 * Wait for a grace period to elapse.  But it is illegal to invoke
 * synchronize_sched() from within an RCU read-side critical section.
 * Therefore, any legal call to synchronize_sched() is a quiescent
 * state, and so on a UP system, synchronize_sched() need do nothing.
 * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 * benefits of doing might_sleep() to reduce latency.)
 *
 * Cool, huh?  (Due to Josh Triplett.)
 *
 * But we want to make this a static inline later.  The cond_resched()
 * currently makes this problematic.
 */
void synchronize_sched(void)
{
	cond_resched();
}
EXPORT_SYMBOL_GPL(synchronize_sched);

/*
 * Helper function for call_rcu() and call_rcu_bh().
 */
static void __call_rcu(struct rcu_head *head,
		       void (*func)(struct rcu_head *rcu),
		       struct rcu_ctrlblk *rcp)
{
	unsigned long flags;

	debug_rcu_head_queue(head);
	head->func = func;
	head->next = NULL;

	local_irq_save(flags);
	*rcp->curtail = head;
	rcp->curtail = &head->next;
	RCU_TRACE(rcp->qlen++);
	local_irq_restore(flags);
}

/*
 * Post an RCU callback to be invoked after the end of an RCU-sched grace
 * period.  But since we have but one CPU, that would be after any
 * quiescent state.
 */
void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
	__call_rcu(head, func, &rcu_sched_ctrlblk);
}
EXPORT_SYMBOL_GPL(call_rcu_sched);

/*
 * Post an RCU bottom-half callback to be invoked after any subsequent
 * quiescent state.
 */
void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
	__call_rcu(head, func, &rcu_bh_ctrlblk);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);