[PATCH pm-freezer 3/4] freezer: check freezing() before leaving FROZEN state
Oleg Nesterov
oleg at redhat.com
Mon Aug 29 10:12:28 PDT 2011
On 08/29, Oleg Nesterov wrote:
>
> On 08/29, Tejun Heo wrote:
> >
> > --- work.orig/kernel/freezer.c
> > +++ work/kernel/freezer.c
> > @@ -60,6 +60,7 @@ bool __refrigerator(bool check_kthr_stop
> > */
> > spin_lock_irq(&freezer_lock);
> > current->flags |= PF_FROZEN;
> > +refreeze:
> > spin_unlock_irq(&freezer_lock);
> >
> > save = current->state;
> > @@ -78,8 +79,10 @@ bool __refrigerator(bool check_kthr_stop
> > schedule();
> > }
> >
> > - /* leave FROZEN */
> > + /* leave FROZEN after checking freezing() holding freezer_lock */
> > spin_lock_irq(&freezer_lock);
> > + if (freezing(current))
> > + goto refreeze;
>
> Looks like, you should move "save = current->state" up then.
Hmm. And afaics there is another problem. This can "livelock" if
check_kthr_stop && kthread_should_stop().
May be we should consolidate the freezer_lock's sections, something
like below?
Hmm. But I got lost a bit. Why do we need freezer_lock to set/clear
PF_FROZEN ? OK, the code below takes freezer_lock for freezing().
Is there any other reason?
Oleg.
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;
save = current->state;
pr_debug("%s entered refrigerator\n", current->comm);
for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);
spin_lock_irq(&freezer_lock);
current->flags |= PF_FROZEN;
if (!freezing(current) ||
(check_kthr_stop && kthread_should_stop()))
current->flags &= ~PF_FROZEN;
spin_unlock_irq(&freezer_lock);
if (!current->flags & PF_FROZEN)
break;
was_frozen = true;
schedule();
}
spin_lock_irq(¤t->sighand->siglock);
recalc_sigpending(); /* We sent fake signal, clean it up */
spin_unlock_irq(¤t->sighand->siglock);
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;
}
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