From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>,
Oleg Nesterov <oleg@redhat.com>,
David Rientjes <rientjes@google.com>,
syzbot <syzbot+bab151e82a4e973fa325@syzkaller.appspotmail.com>,
cgroups@vger.kernel.org, hannes@cmpxchg.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
syzkaller-bugs@googlegroups.com,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: WARNING in try_charge
Date: Fri, 10 Aug 2018 06:05:19 +0900 [thread overview]
Message-ID: <56c95100-d7f9-b715-bdec-e8bb112e2630@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20180809150735.GA15611@dhcp22.suse.cz>
On 2018/08/10 0:07, Michal Hocko wrote:
> On Thu 09-08-18 22:57:43, Tetsuo Handa wrote:
>> >From b1f38168f14397c7af9c122cd8207663d96e02ec Mon Sep 17 00:00:00 2001
>> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>> Date: Thu, 9 Aug 2018 22:49:40 +0900
>> Subject: [PATCH] mm, oom: task_will_free_mem(current) should retry until
>> memory reserve fails
>>
>> Commit 696453e66630ad45 ("mm, oom: task_will_free_mem should skip
>> oom_reaped tasks") changed to select next OOM victim as soon as
>> MMF_OOM_SKIP is set. But we don't need to select next OOM victim as
>> long as ALLOC_OOM allocation can succeed. And syzbot is hitting WARN(1)
>> caused by this race window [1].
>
> It is not because the syzbot was exercising a completely different code
> path (memcg charge rather than the page allocator).
I know syzbot is hitting memcg charge path.
>
>> Since memcg OOM case uses forced charge if current thread is killed,
>> out_of_memory() can return true without selecting next OOM victim.
>> Therefore, this patch changes task_will_free_mem(current) to ignore
>> MMF_OOM_SKIP unless ALLOC_OOM allocation failed.
>
> And the patch is simply wrong for memcg.
>
Why? I think I should have done
-+ page = __alloc_pages_may_oom(gfp_mask, order, alloc_flags == ALLOC_OOM
-+ || (gfp_mask & __GFP_NOMEMALLOC), ac,
-+ &did_some_progress);
++ page = __alloc_pages_may_oom(gfp_mask, order, alloc_flags == ALLOC_OOM,
++ ac, &did_some_progress);
because nobody will use __GFP_NOMEMALLOC | __GFP_NOFAIL. But for memcg charge
path, task_will_free_mem(current, false) == true and out_of_memory() will return
true, which avoids unnecessary OOM killing.
Of course, this patch cannot avoid unnecessary OOM killing if out_of_memory()
is called by not yet killed process. But to mitigate it, what can we do other
than defer setting MMF_OOM_SKIP using a timeout based mechanism? Making
the OOM reaper unconditionally reclaim all memory is not a valid answer.
next prev parent reply other threads:[~2018-08-09 21:05 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-04 13:33 WARNING in try_charge syzbot
2018-08-04 13:45 ` Tetsuo Handa
2018-08-05 11:33 ` Tetsuo Handa
2018-08-05 8:14 ` syzbot
2018-08-06 9:15 ` Michal Hocko
2018-08-06 9:30 ` Dmitry Vyukov
2018-08-06 9:48 ` Michal Hocko
2018-08-06 10:34 ` Dmitry Vyukov
2018-08-06 11:02 ` Michal Hocko
2018-08-06 11:57 ` Dmitry Vyukov
2018-08-06 14:21 ` Michal Hocko
2018-08-06 14:58 ` Dmitry Vyukov
2018-08-06 17:30 ` Michal Hocko
2018-08-06 17:53 ` Dmitry Vyukov
2018-08-06 15:07 ` Dmitry Vyukov
2018-08-06 15:31 ` Johannes Weiner
2018-08-06 10:39 ` Dmitry Vyukov
2018-08-06 10:47 ` Tetsuo Handa
2018-08-06 11:09 ` Michal Hocko
2018-08-06 11:27 ` syzbot
2018-08-06 11:32 ` Michal Hocko
2018-08-06 11:58 ` Dmitry Vyukov
2018-08-06 14:41 ` Tetsuo Handa
2018-08-06 14:58 ` Michal Hocko
2018-08-06 15:12 ` Tetsuo Handa
2018-08-06 14:54 ` David Howells
2018-08-06 15:04 ` Tetsuo Handa
2018-08-06 11:00 ` syzbot
2018-08-06 15:32 ` Tetsuo Handa
2018-08-06 15:42 ` syzbot
2018-08-06 16:02 ` Tetsuo Handa
2018-08-06 17:44 ` Michal Hocko
2018-08-06 17:49 ` Dmitry Vyukov
2018-08-06 17:56 ` Michal Hocko
2018-08-06 18:13 ` Michal Hocko
2018-08-06 18:23 ` syzbot
2018-08-06 18:55 ` Michal Hocko
2018-08-06 19:12 ` syzbot
2018-08-06 19:45 ` Michal Hocko
2018-08-06 19:46 ` Michal Hocko
2018-08-07 11:18 ` Dmitry Vyukov
2018-08-07 11:25 ` Michal Hocko
2018-08-06 18:39 ` Michal Hocko
2018-08-06 20:26 ` Tetsuo Handa
2018-08-06 20:34 ` Michal Hocko
2018-08-06 20:46 ` Tetsuo Handa
2018-08-06 20:55 ` Michal Hocko
2018-08-06 21:50 ` Tetsuo Handa
2018-08-07 10:19 ` Tetsuo Handa
2018-08-09 13:57 ` Tetsuo Handa
2018-08-09 15:07 ` Michal Hocko
2018-08-09 21:05 ` Tetsuo Handa [this message]
2018-08-09 15:34 ` Johannes Weiner
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