On Sat 09-01-16 20:04:45, Tetsuo Handa wrote:
> While oom_killer_disable() is called by freeze_processes() after all user
> threads except the current thread are frozen, it is possible that kernel
> threads invoke the OOM killer and sends SIGKILL to the current thread due
> to sharing the thawed victim's memory. Therefore, checking for SIGKILL is
> preferable than TIF_MEMDIE.
OK, this sounds like a good idea. Reducing TIF_MEMDIE usage outside of
the oom/mm proper is indeed desirable.
> Also, it is possible that the thawed victim fails to terminate due to
> invisible dependency. Therefore, waiting with timeout is preferable.
> The timeout is copied from __usermodehelper_disable() called by
> freeze_processes().
__usermodehelper_disable and oom_killer_disable do follow a similar
pattern so it is probably a good idea to handle them the same way. I
would just ask this to be in a separate patch and ideally share the same
constant rather than a magic constant.
Thanks!
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> ---
> mm/oom_kill.c | 18 ++++++++----------
> 1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index b8a4210..bafa6b2 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -612,21 +612,19 @@ void exit_oom_victim(void)
> bool oom_killer_disable(void)
> {
> /*
> - * Make sure to not race with an ongoing OOM killer
> - * and that the current is not the victim.
> + * Make sure to not race with an ongoing OOM killer. Check that the
> + * current is not killed (possibly due to sharing the victim's memory).
> */
> - mutex_lock(&oom_lock);
> - if (test_thread_flag(TIF_MEMDIE)) {
> - mutex_unlock(&oom_lock);
> + if (mutex_lock_killable(&oom_lock))
> return false;
> - }
> -
> oom_killer_disabled = true;
> mutex_unlock(&oom_lock);
>
> - wait_event(oom_victims_wait, !atomic_read(&oom_victims));
> -
> - return true;
> + /* Do not wait forever in case existing victims got stuck. */
> + if (!wait_event_timeout(oom_victims_wait, !atomic_read(&oom_victims),
> + 5 * HZ))
> + oom_killer_disabled = false;
> + return oom_killer_disabled;
> }
>
> /**
> --
> 1.8.3.1
>
> --
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--
Michal Hocko
SUSE Labs
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