Re: [PATCH] mm,oom: use per signal_struct flag rather than clear TIF_MEMDIE

[Oleg Nesterov <oleg@redhat.com>]

On 06/25, Tetsuo Handa wrote:
>
> Oleg Nesterov wrote:
> > And in any case I don't understand this patch but I have to admit that
> > I failed to force myself to read the changelog and the actual change ;)
> > In any case I agree that we should not set MMF_MEMDIE if ->mm == NULL,
> > and if we ensure this then I do not understand why we can't rely on
> > MMF_OOM_REAPED. Ignoring the obvious races, if ->oom_victims != 0 then
> > find_lock_task_mm() should succed.
>
> Since we are using
>
>   mm = current->mm;
>   current->mm = NULL;
>   __mmput(mm); (may block for unbounded period waiting for somebody else's memory allocation)
>   exit_oom_victim(current);
>
> sequence, we won't be able to make find_lock_task_mm(tsk) != NULL when
> tsk->signal->oom_victims != 0 unless we change this sequence.

Ah, but this is clear, note the "Ignoring the obvious races" above.
Can't we fix this race? I am a bit lost, but iirc we want this anyway
to ensure that we do not set TIF_MEMDIE if ->mm == NULL ?

Hmm. Although I am not sure I really understand the "may block for
unbounded period ..." above. Do you mean khugepaged_exit?

Oleg.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>