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SubjectRe: [PATCH 09/16] freezer: make freezing indicate freeze condition in effect
On 08/19, Tejun Heo wrote:
>
> 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.

but this looks racy.

> @@ -44,7 +48,7 @@ bool __refrigerator(bool check_kthr_stop)
>
> for (;;) {
> set_current_state(TASK_UNINTERRUPTIBLE);
> - if (!frozen(current) ||
> + if (!freezing(current) ||
> (check_kthr_stop && kthread_should_stop()))
> break;
> was_frozen = true;
> @@ -54,6 +58,11 @@ bool __refrigerator(bool check_kthr_stop)
> /* Remove the accounting blocker */
> current->flags &= ~PF_FREEZING;
>
> + /* leave FROZEN */
> + spin_lock_irq(&freezer_lock);
> + current->flags &= ~PF_FROZEN;
> + spin_unlock_irq(&freezer_lock);

What if freezing() is true again when we are going to clear
PF_FROZEN?

In this case the 2nd try_to_freeze_tasks() can see this task
as already frozen and return success while it is going to run.

Oleg.



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