linux-kernel - Re: [Patch] freezer: check OOM kill signal while being frozen

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Date:	Sat, 9 Aug 2014 11:00:18 +0900
From:	Kyungmin Park <kmpark@...radead.org>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>,
	Michal Hocko <mhocko@...e.cz>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [Patch] freezer: check OOM kill signal while being frozen

On Sat, Aug 9, 2014 at 9:46 AM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> There is a race condition between OOM killer and freezer when
> they try to operate on the same process, something like below:
>
>         Process A       Process B               Process C
> trigger oom
> B=oom_scan_process_thread()
>                                         cgroup_freezer_freeze(B)
>                         ...
>                         try_to_freeze()
>                         stay in D state
> oom_kill_process(B)
>
> In this case, process A triggers OOM and kernel selects process B
> as the victim, right before being killed process B was frozen by
> process C therefore went to D state, then kernel sent SIGKILL but
> it is already too late as process B will never care about pending
> signals any more. Fix this straightly by checking fatal pending signal
> from OOM killer, so that the frozen process will recover itself
> and then be killed finally.

Similar patch is posted and discussed but no conclusion.
http://marc.info/?t=137699769400004&r=1&w=1

Adding Bart,

Thank you,
Kyungmin Park
>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Michal Hocko <mhocko@...e.cz>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> ---
> diff --git a/kernel/freezer.c b/kernel/freezer.c
> index aa6a8aa..c6d189d 100644
> --- a/kernel/freezer.c
> +++ b/kernel/freezer.c
> @@ -68,7 +68,9 @@ bool __refrigerator(bool check_kthr_stop)
>                 spin_lock_irq(&freezer_lock);
>                 current->flags |= PF_FROZEN;
>                 if (!freezing(current) ||
> -                   (check_kthr_stop && kthread_should_stop()))
> +                   (check_kthr_stop && kthread_should_stop()) ||
> +                   (test_tsk_thread_flag(current, TIF_MEMDIE) &&
> +                        fatal_signal_pending(current)))
>                         current->flags &= ~PF_FROZEN;
>                 spin_unlock_irq(&freezer_lock);
>
> --
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