Michal Hocko wrote:
> Hi,
> I was thinking about this and I am more and more convinced that we
> shouldn't care about panic_on_oom=2 configuration for now and go with
> the simplest solution first. I have revisited my original patch and
> replaced delayed work by a timer based on the feedback from Tetsuo.
>
To me, obsolating panic_on_oom > 0 sounds cleaner.
> I think we can rely on timers. A downside would be that we cannot dump
> the full OOM report from the IRQ context because we rely on task_lock
> which is not IRQ safe. But I do not think we really need it. An OOM
> report will be in the log already most of the time and show_mem will
> tell us the current memory situation.
>
> What do you think?
We can rely on timers, but we can't rely on global timer.
> + if (sysctl_panic_on_oom_timeout) {
> + if (sysctl_panic_on_oom > 1) {
> + pr_warn("panic_on_oom_timeout is ignored for panic_on_oom=2\n");
> + } else {
> + /*
> + * Only schedule the delayed panic_on_oom when this is
> + * the first OOM triggered. oom_lock will protect us
> + * from races
> + */
> + if (atomic_read(&oom_victims))
> + return;
> +
> + mod_timer(&panic_on_oom_timer,
> + jiffies + (sysctl_panic_on_oom_timeout * HZ));
> + return;
> + }
> + }
Since this version uses global panic_on_oom_timer, you cannot handle
OOM race like below.
(1) p1 in memcg1 calls out_of_memory().
(2) 5 seconds of timeout is started by p1.
(3) p1 takes 3 seconds for some reason.
(4) p2 in memcg2 calls out_of_memory().
(5) p1 calls unmark_oom_victim() but timer continues.
(6) p2 takes 2 seconds for some reason.
(7) 5 seconds of timeout expires despite individual delay was less than
5 seconds.
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