From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: mhocko@kernel.org
Cc: linux-mm@kvack.org, rientjes@google.com, oleg@redhat.com,
vdavydov@parallels.com, akpm@linux-foundation.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 07/10] mm, oom: fortify task_will_free_mem
Date: Sat, 11 Jun 2016 17:10:03 +0900 [thread overview]
Message-ID: <201606111710.IGF51027.OJLSOQtHVOFFFM@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20160609142026.GF24777@dhcp22.suse.cz>
Michal Hocko wrote:
> > Also, I think setting TIF_MEMDIE on p when find_lock_task_mm(p) != p is
> > wrong. While oom_reap_task() will anyway clear TIF_MEMDIE even if we set
> > TIF_MEMDIE on p when p->mm == NULL, it is not true for CONFIG_MMU=n case.
>
> Yes this would be racy for !CONFIG_MMU but does it actually matter?
I don't know because I've never used CONFIG_MMU=n kernels. But I think it
actually matters. You fixed this race by commit 83363b917a2982dd ("oom:
make sure that TIF_MEMDIE is set under task_lock").
> > > @@ -940,14 +968,10 @@ bool out_of_memory(struct oom_control *oc)
> > > * If current has a pending SIGKILL or is exiting, then automatically
> > > * select it. The goal is to allow it to allocate so that it may
> > > * quickly exit and free its memory.
> > > - *
> > > - * But don't select if current has already released its mm and cleared
> > > - * TIF_MEMDIE flag at exit_mm(), otherwise an OOM livelock may occur.
> > > */
> > > - if (current->mm &&
> > > - (fatal_signal_pending(current) || task_will_free_mem(current))) {
> > > + if (task_will_free_mem(current)) {
> >
> > Setting TIF_MEMDIE on current when current->mm == NULL and
> > find_lock_task_mm(current) != NULL is wrong.
>
> Why? Or is this still about the !CONFIG_MMU?
Yes, mainly about CONFIG_MMU=n kernels. This change reintroduces possibility
of failing to clear TIF_MEMDIE which was fixed by commit d7a94e7e11badf84
("oom: don't count on mm-less current process").
I was also thinking about possibility of the OOM reaper failing to clear
TIF_MEMDIE due to race with PM/freezing. That is, TIF_MEMDIE is set on a
thread which already released mm, then try_to_freeze_tasks(true) from
freeze_processes() freezes such thread, then oom_reap_task() fails to
clear TIF_MEMDIE from such thread due to oom_killer_disabled == true, then
subsequent memory allocation fails and hibernation aborts, then all threads
are thawed, but TIF_MEMDIE thread won't clear TIF_MEMDIE, and finally the
system locks up because nobody will clear TIF_MEMDIE.
But as I posted in other thread, we can use an approach which does not
introduce possibility of failing to clear TIF_MEMDIE due to race with
PM/freezing. So, this is purely about CONFIG_MMU=n kernels.
next prev parent reply other threads:[~2016-06-11 8:10 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-09 11:52 [PATCH 0/10 -v4] Handle oom bypass more gracefully Michal Hocko
2016-06-09 11:52 ` [PATCH 01/10] proc, oom: drop bogus task_lock and mm check Michal Hocko
2016-06-09 11:52 ` [PATCH 02/10] proc, oom: drop bogus sighand lock Michal Hocko
2016-06-09 11:52 ` [PATCH 03/10] proc, oom_adj: extract oom_score_adj setting into a helper Michal Hocko
2016-06-09 11:52 ` [PATCH 04/10] mm, oom_adj: make sure processes sharing mm have same view of oom_score_adj Michal Hocko
2016-06-15 15:03 ` Oleg Nesterov
2016-06-09 11:52 ` [PATCH 05/10] mm, oom: skip vforked tasks from being selected Michal Hocko
2016-06-15 14:51 ` Oleg Nesterov
2016-06-16 6:24 ` Michal Hocko
2016-06-09 11:52 ` [PATCH 06/10] mm, oom: kill all tasks sharing the mm Michal Hocko
2016-06-09 11:52 ` [PATCH 07/10] mm, oom: fortify task_will_free_mem Michal Hocko
2016-06-09 13:18 ` Tetsuo Handa
2016-06-09 14:20 ` Michal Hocko
2016-06-11 8:10 ` Tetsuo Handa [this message]
2016-06-13 11:27 ` Michal Hocko
2016-06-16 12:54 ` Tetsuo Handa
2016-06-16 14:29 ` Michal Hocko
2016-06-16 15:40 ` Tetsuo Handa
2016-06-16 15:53 ` Michal Hocko
2016-06-17 11:38 ` Tetsuo Handa
2016-06-17 12:26 ` Michal Hocko
2016-06-17 13:12 ` Tetsuo Handa
2016-06-17 13:29 ` Michal Hocko
2016-06-09 11:52 ` [PATCH 08/10] mm, oom: task_will_free_mem should skip oom_reaped tasks Michal Hocko
2016-06-17 11:35 ` Tetsuo Handa
2016-06-17 12:56 ` Michal Hocko
2016-06-09 11:52 ` [PATCH 09/10] mm, oom_reaper: do not attempt to reap a task more than twice Michal Hocko
2016-06-15 14:48 ` Oleg Nesterov
2016-06-16 6:28 ` Michal Hocko
2016-06-09 11:52 ` [PATCH 10/10] mm, oom: hide mm which is shared with kthread or global init Michal Hocko
2016-06-09 15:15 ` Tetsuo Handa
2016-06-09 15:41 ` Michal Hocko
2016-06-16 13:15 ` Tetsuo Handa
2016-06-16 13:36 ` Tetsuo Handa
2016-06-15 14:37 ` Oleg Nesterov
2016-06-16 6:31 ` Michal Hocko
2016-06-13 11:23 ` [PATCH 0/10 -v4] Handle oom bypass more gracefully Michal Hocko
2016-06-13 14:13 ` Michal Hocko
2016-06-14 20:17 ` Oleg Nesterov
2016-06-14 20:44 ` Oleg Nesterov
2016-06-16 6:33 ` Michal Hocko
2016-06-15 15:09 ` Oleg Nesterov
2016-06-16 6:34 ` Michal Hocko
-- strict thread matches above, loose matches on Subject: below --
2016-06-20 12:43 [PATCH 0/10 -v5] " Michal Hocko
2016-06-20 12:43 ` [PATCH 07/10] mm, oom: fortify task_will_free_mem Michal Hocko
2016-06-03 9:16 [PATCH 0/10 -v3] Handle oom bypass more gracefully Michal Hocko
2016-06-03 9:16 ` [PATCH 07/10] mm, oom: fortify task_will_free_mem Michal Hocko
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