On Mon 12-09-16 20:32:13, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > On Sat 10-09-16 02:28:40, Tetsuo Handa wrote:
> > > Commit c32b3cbe0d067a9c ("oom, PM: make OOM detection in the freezer path
> > > raceless") inserted a WARN_ON() into pagefault_out_of_memory() in order
> > > to warn when we raced with disabling the OOM killer. But emitting same
> > > backtrace forever after the OOM killer/reaper are disabled is pointless
> > > because the system is already OOM livelocked.
> >
> > How that would that be forever? Pagefaults are not GFP_NOFAIL and the
> > killed task would just enter the exit path.
>
> Indeed, there is
>
> /* Avoid allocations with no watermarks from looping endlessly */
> if (test_thread_flag(TIF_MEMDIE) && !(gfp_mask & __GFP_NOFAIL))
> goto nopage;
>
> check.
>
> I don't know if pagefaults can happen after entering do_exit().
It can via g-u-p but callers should be able to handle the failure.
[...]
> Subject: [PATCH v2] mm: Don't emit warning from pagefault_out_of_memory()
> Date: Sat, 10 Sep 2016 02:28:40 +0900
> Message-Id: <1473442120-7246-1-git-send-email-penguin-kernel@xxxxxxxxxxxxxxxxxxx>
>
> Commit c32b3cbe0d067a9c ("oom, PM: make OOM detection in the freezer path
> raceless") inserted a WARN_ON() into pagefault_out_of_memory() in order
> to warn when we raced with disabling the OOM killer.
>
> Now, patch "oom, suspend: fix oom_killer_disable vs. pm suspend properly"
> introduced a timeout for oom_killer_disable(). Even if we raced with
> disabling the OOM killer and the system is OOM livelocked, the OOM killer
> will be enabled eventually (in 20 seconds by default) and the OOM livelock
> will be solved. Therefore, we no longer need to warn when we raced with
> disabling the OOM killer.
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
> ---
> mm/oom_kill.c | 12 +-----------
> 1 file changed, 1 insertion(+), 11 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 0034baf..f284e92 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -1069,16 +1069,6 @@ void pagefault_out_of_memory(void)
>
> if (!mutex_trylock(&oom_lock))
> return;
> -
> - if (!out_of_memory(&oc)) {
> - /*
> - * There shouldn't be any user tasks runnable while the
> - * OOM killer is disabled, so the current task has to
> - * be a racing OOM victim for which oom_killer_disable()
> - * is waiting for.
> - */
> - WARN_ON(test_thread_flag(TIF_MEMDIE));
> - }
> -
> + out_of_memory(&oc);
> mutex_unlock(&oom_lock);
> }
> --
> 1.8.3.1
--
Michal Hocko
SUSE Labs
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