Re: [PATCH 1/3 for 2.6.38] oom: oom_kill_process: don't set TIF_MEMDIE if !p->mm

[Oleg Nesterov <oleg@redhat.com>]

On 03/14, David Rientjes wrote:
>
> On Mon, 14 Mar 2011, Oleg Nesterov wrote:
>
> > oom_kill_process() simply sets TIF_MEMDIE and returns if PF_EXITING.
> > This is very wrong by many reasons. In particular, this thread can
> > be the dead group leader. Check p->mm != NULL.
> >
>
> This is true only for the oom_kill_allocating_task sysctl where it is
> required in all cases to kill current; current won't be triggering the oom
> killer if it's dead.
>
> oom_kill_process() is called with the thread selected by
> select_bad_process() and that function will not return any thread if any
> eligible task is found to be PF_EXITING and is not current, or any
> eligible task is found to have TIF_MEMDIE.
>
> In other words, for this conditional to be true in oom_kill_process(),
> then p must be current and so it cannot be the dead group leader as
> specified in your changelog unless PF_EXITING gets set between
> select_bad_process() and the oom_kill_process() call: we don't care about
> that since it's in the exit path and we therefore want to give it access
> to memory reserves to quickly exit anyway and the check for PF_EXITING in
> select_bad_process() prevents any infinite loop of that task getting
> constantly reselected if it's dead.

Confused. I sent the test-case. OK, may be you meant the code in -mm,
but I meant the current code.

Oleg.