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

Oleg Nesterov
2007-07-10T20:35:05Z

On 07/10, Rafael J. Wysocki wrote:
>
> On Tuesday, 10 July 2007 20:50, Oleg Nesterov wrote:
> >
> > 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
>
> The retry mechanism only applies to user land processes. :-)
>
> > 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.
>
> PF_FROZEN and TIF_FREEZE are mutually exclusive as long as the thawing is
> not racing with refrigerator().

Ah yes, I forgot. Thanks!

> > Another problem is that we only count UNINTERRUPTIBLE tasks to make a decision
> > about retry, while wait_event_freezable() sleeps NTERRUPTIBLE.
>
> The retry thing doesn't cover kernel threads, because they aren't supposed to
> block the freezer. They are supposed to freeze voluntarily and to know
> _exactly_ what they are doing.

Ok, I see... So, the plan is to eventually fix the "problematic" things like
kthread_stop(), yes? Unless I missed something again, we can't reliably
kthread_stop() the thread above even if it does

wait_event_freezable(my_condition || kthread_should_stop())

Oleg.