rcutiny.c

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/*
 * 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 <[email protected]>
 *
 * 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 = DYNTICK_TASK_EXIT_IDLE;

/* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
static void rcu_idle_enter_common(long long newval)
{
    if (newval) {
        RCU_TRACE(trace_rcu_dyntick("--=",
                        rcu_dynticks_nesting, newval));
        rcu_dynticks_nesting = newval;
        return;
    }
    RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting, newval));
    if (!is_idle_task(current)) {
        struct task_struct *idle = idle_task(smp_processor_id());

        RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
                        rcu_dynticks_nesting, newval));
        ftrace_dump(DUMP_ALL);
        WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
              current->pid, current->comm,
              idle->pid, idle->comm); /* must be idle task! */
    }
    rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
    barrier();
    rcu_dynticks_nesting = newval;
}

/*
 * 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;
    long long newval;

    local_irq_save(flags);
    WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
    if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
        DYNTICK_TASK_NEST_VALUE)
        newval = 0;
    else
        newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE;
    rcu_idle_enter_common(newval);
    local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_enter);

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

    local_irq_save(flags);
    newval = rcu_dynticks_nesting - 1;
    WARN_ON_ONCE(newval < 0);
    rcu_idle_enter_common(newval);
    local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_irq_exit);

/* 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("++=",
                        oldval, rcu_dynticks_nesting));
        return;
    }
    RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
    if (!is_idle_task(current)) {
        struct task_struct *idle = idle_task(smp_processor_id());

        RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
              oldval, rcu_dynticks_nesting));
        ftrace_dump(DUMP_ALL);
        WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
              current->pid, current->comm,
              idle->pid, idle->comm); /* must be idle task! */
    }
}

/*
 * 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(rcu_dynticks_nesting < 0);
    if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
        rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
    else
        rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
    rcu_idle_exit_common(oldval);
    local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_exit);

/*
 * 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);
}
EXPORT_SYMBOL_GPL(rcu_irq_enter);

#ifdef CONFIG_DEBUG_LOCK_ALLOC

/*
 * 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_DEBUG_LOCK_ALLOC */

/*
 * 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, 0, -1));
        RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
                          ACCESS_ONCE(rcp->rcucblist),
                          need_resched(),
                          is_idle_task(current),
                          rcu_is_callbacks_kthread()));
        return;
    }

    /* Move the ready-to-invoke callbacks to a local list. */
    local_irq_save(flags);
    RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -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, 0, need_resched(),
                      is_idle_task(current),
                      rcu_is_callbacks_kthread()));
}

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)
{
    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_sched() in RCU read-side critical section");
    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);