linux/kernel/freezer.c
Tejun Heo 6907483b4e freezer: make freezing indicate freeze condition in effect
Currently freezing (TIF_FREEZE) and frozen (PF_FROZEN) states are
interlocked - freezing is set to request freeze and when the task
actually freezes, it clears freezing and sets frozen.

This interlocking makes things more complex than necessary - freezing
doesn't mean there's freezing condition in effect and frozen doesn't
match the task actually entering and leaving frozen state (it's
cleared by the thawing task).

This patch makes freezing indicate that freeze condition is in effect.
A task enters and stays frozen if freezing.  This makes PF_FROZEN
manipulation done only by the task itself and prevents wakeup from
__thaw_task() leaking outside of refrigerator.

The only place which needs to tell freezing && !frozen is
try_to_freeze_task() to whine about tasks which don't enter frozen.
It's updated to test the condition explicitly.

With the change, frozen() state my linger after __thaw_task() until
the task wakes up and exits fridge.  This can trigger BUG_ON() in
update_if_frozen().  Work it around by testing freezing() && frozen()
instead of frozen().

-v2: Oleg pointed out missing re-check of freezing() when trying to
     clear FROZEN and possible spurious BUG_ON() trigger in
     update_if_frozen().  Both fixed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Menage <paul@paulmenage.org>
2011-11-21 12:32:24 -08:00

168 lines
4.2 KiB
C

/*
* kernel/freezer.c - Function to freeze a process
*
* Originally from kernel/power/process.c
*/
#include <linux/interrupt.h>
#include <linux/suspend.h>
#include <linux/export.h>
#include <linux/syscalls.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
/* protects freezing and frozen transitions */
static DEFINE_SPINLOCK(freezer_lock);
/* Refrigerator is place where frozen processes are stored :-). */
bool __refrigerator(bool check_kthr_stop)
{
/* Hmm, should we be allowed to suspend when there are realtime
processes around? */
bool was_frozen = false;
long save;
/*
* Enter FROZEN. If NOFREEZE, schedule immediate thawing by
* clearing freezing.
*/
spin_lock_irq(&freezer_lock);
repeat:
if (!freezing(current)) {
spin_unlock_irq(&freezer_lock);
return was_frozen;
}
if (current->flags & PF_NOFREEZE)
clear_freeze_flag(current);
current->flags |= PF_FROZEN;
spin_unlock_irq(&freezer_lock);
save = current->state;
pr_debug("%s entered refrigerator\n", current->comm);
spin_lock_irq(&current->sighand->siglock);
recalc_sigpending(); /* We sent fake signal, clean it up */
spin_unlock_irq(&current->sighand->siglock);
/* prevent accounting of that task to load */
current->flags |= PF_FREEZING;
for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (!freezing(current) ||
(check_kthr_stop && kthread_should_stop()))
break;
was_frozen = true;
schedule();
}
/* Remove the accounting blocker */
current->flags &= ~PF_FREEZING;
/* leave FROZEN */
spin_lock_irq(&freezer_lock);
if (freezing(current))
goto repeat;
current->flags &= ~PF_FROZEN;
spin_unlock_irq(&freezer_lock);
pr_debug("%s left refrigerator\n", current->comm);
/*
* Restore saved task state before returning. The mb'd version
* needs to be used; otherwise, it might silently break
* synchronization which depends on ordered task state change.
*/
set_current_state(save);
return was_frozen;
}
EXPORT_SYMBOL(__refrigerator);
static void fake_signal_wake_up(struct task_struct *p)
{
unsigned long flags;
spin_lock_irqsave(&p->sighand->siglock, flags);
signal_wake_up(p, 0);
spin_unlock_irqrestore(&p->sighand->siglock, flags);
}
/**
* freeze_task - send a freeze request to given task
* @p: task to send the request to
* @sig_only: if set, the request will only be sent if the task has the
* PF_FREEZER_NOSIG flag unset
* Return value: 'false', if @sig_only is set and the task has
* PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
*
* The freeze request is sent by setting the tasks's TIF_FREEZE flag and
* either sending a fake signal to it or waking it up, depending on whether
* or not it has PF_FREEZER_NOSIG set. If @sig_only is set and the task
* has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
* TIF_FREEZE flag will not be set.
*/
bool freeze_task(struct task_struct *p, bool sig_only)
{
unsigned long flags;
bool ret = false;
spin_lock_irqsave(&freezer_lock, flags);
if (sig_only && !should_send_signal(p))
goto out_unlock;
if (frozen(p))
goto out_unlock;
set_freeze_flag(p);
if (should_send_signal(p)) {
fake_signal_wake_up(p);
/*
* fake_signal_wake_up() goes through p's scheduler
* lock and guarantees that TASK_STOPPED/TRACED ->
* TASK_RUNNING transition can't race with task state
* testing in try_to_freeze_tasks().
*/
} else {
wake_up_state(p, TASK_INTERRUPTIBLE);
}
ret = true;
out_unlock:
spin_unlock_irqrestore(&freezer_lock, flags);
return ret;
}
void cancel_freezing(struct task_struct *p)
{
unsigned long flags;
spin_lock_irqsave(&freezer_lock, flags);
if (freezing(p)) {
pr_debug(" clean up: %s\n", p->comm);
clear_freeze_flag(p);
spin_lock(&p->sighand->siglock);
recalc_sigpending_and_wake(p);
spin_unlock(&p->sighand->siglock);
}
spin_unlock_irqrestore(&freezer_lock, flags);
}
void __thaw_task(struct task_struct *p)
{
unsigned long flags;
/*
* Clear freezing and kick @p if FROZEN. Clearing is guaranteed to
* be visible to @p as waking up implies wmb. Waking up inside
* freezer_lock also prevents wakeups from leaking outside
* refrigerator.
*/
spin_lock_irqsave(&freezer_lock, flags);
clear_freeze_flag(p);
if (frozen(p))
wake_up_process(p);
spin_unlock_irqrestore(&freezer_lock, flags);
}