Re: [patch] oom: thaw threads if oom killed thread is frozen before deferring

Oleg Nesterov
2011-09-29T12:09:33Z

On 09/29, Michal Hocko wrote:
>
> --- a/kernel/freezer.c
> +++ b/kernel/freezer.c
> @@ -48,6 +48,10 @@ void refrigerator(void)
> current->flags |= PF_FREEZING;
>
> for (;;) {
> + if (fatal_signal_pending(current)) {
> + current->flags &= ~PF_FROZEN;

We can't do this.

If PF_FROZEN was set, we must not modify current->flags, this can
race with, say, thaw_process().

OK, we can take task_lock(), but this doesn't close other races.
Say, a SIGKILL'ed task can do try_to_freeze(). Perhaps we should
simply call thaw_process() unconditionally, this also clears
TIF_FREEZE. Or check freezing() || frozen(). Afacis this solves
the race you described.

But of course this can't help if freeze_task() is called later.
May be freezable() should check TIF_MEMDIE...

Oleg.