Re: Re: [RFC][PATCH -mm 5/6] Freezer: Use freezing timeout more efficiently

Oleg Nesterov
2007-07-10T18:50:59Z

On 07/10, Rafael J. Wysocki wrote:
>
> + if (todo && freeze_user_space && !time_after(jiffies, end_time)) {
> + /*
> + * Some tasks have not been able to freeze. They might be stuck
> + * in TASK_UNINTERRUPTIBLE waiting for the frozen tasks. Try to
> + * thaw the tasks that have frozen without clearing the freeze
> + * requests of the remaining tasks and repeat.
> + */
> + read_lock(&tasklist_lock);
> + do_each_thread(g, p) {
> + if (frozen(p)) {
> + p->flags &= ~PF_FROZEN;
> + wake_up_process(p);

I just noticed we don't use thaw_process(), this means that the retry doesn't
play well with wait_event_freezable() introduced in the previous patch.

Suppose that kthread_stop(T) hangs and blocks the freezer, and T does

while (!kthread_should_stop()) {
wait_event_freezable(...);
do_something();
}

and it is freezed. We clear PF_FROZEN but not TIF_FREEZE, wait_event_freezable
checks freezing() and goes to refrigerator again.

Another problem is that we only count UNINTERRUPTIBLE tasks to make a decision
about retry, while wait_event_freezable() sleeps NTERRUPTIBLE.

Oleg.