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    SubjectRe: [RFC PATCH(experimental) 2/2] Fix freezer-kthread_stop race
    On 04/19, Gautham R Shenoy wrote:
    >
    > @@ -63,12 +74,16 @@ void refrigerator(void)
    > recalc_sigpending(); /* We sent fake signal, clean it up */
    > spin_unlock_irq(&current->sighand->siglock);
    >
    > + task_lock(current);
    > for (;;) {
    > set_current_state(TASK_UNINTERRUPTIBLE);
    > if (!frozen(current))
    > break;
    > + task_unlock(current);
    > schedule();
    > + task_lock(current);
    > }
    > + task_unlock(current);
    > pr_debug("%s left refrigerator\n", current->comm);
    > current->state = save;

    Just curious, why this change?

    > +int hold_freezer_for_task(struct task_struct *p)
    > +{
    > + int ret = 0;
    > + spin_lock(&freezer_status.lock);
    > + if (freezer_status.count >= 0)
    > + {
    > + set_tsk_thread_flag(p, TIF_FREEZER_HELD);
    > + thaw_process(p);
    > + freezer_status.count++;
    > + ret = 1;
    > + }
    > + spin_unlock(&freezer_status.lock);
    > +
    > + return ret;
    > +}

    I think this can work if it is used only in kthread_stop(). But what if
    another task wants to do hold_freezer_for_task(p) ? freezer_status.count
    is recursive, but TIF_FREEZER_HELD is not. IOW, I believe this is not
    generic enough.

    Also, you are planning to add different freezing states (FE_HOTPLUG_CPU,
    FE_SUSPEND, etc). In that case each of them needs a separate .count, because
    it should be negative when try_to_freeze_tasks() returns. Now consider
    the case when we are doing freeze_processes(FE_A | FE_B) ...

    Oleg.

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