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From: Dmitry Vyukov <dvyukov@google.com>
Date: Wed, 25 Nov 2015 14:08:41 +0100
Message-ID: <CACT4Y+Zn+mK37-mvqDQTyt1Psp6HT2heT0e937SO24F7V1q7PA@mail.gmail.com>
Subject: Re: WARNING in handle_mm_fault
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To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Michal Hocko <mhocko@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>, cgroups@vger.kernel.org, "linux-mm@kvack.org" <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>, syzkaller <syzkaller@googlegroups.com>, Kostya Serebryany <kcc@google.com>, Alexander Potapenko <glider@google.com>, Sasha Levin <sasha.levin@oracle.com>, Eric Dumazet <edumazet@google.com>, Greg Thelen <gthelen@google.com>, Tejun Heo <tj@kernel.org>, Peter Zijlstra <peterz@infradead.org>

On Wed, Nov 25, 2015 at 11:51 AM, Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
> On 2015/11/25 17:44, Michal Hocko wrote:
>> Sasha has reported the same thing some time ago
>> http://www.spinics.net/lists/cgroups/msg14075.html. Tejun had a theory
>> http://www.spinics.net/lists/cgroups/msg14078.html but we never got down
>> to the solution.
>
> Did you check assembly code?
> https://gcc.gnu.org/ml/gcc/2012-02/msg00005.html

If the race described in
http://www.spinics.net/lists/cgroups/msg14078.html does actually
happen, then there is nothing to check.
https://gcc.gnu.org/ml/gcc/2012-02/msg00005.html talks about different
memory locations, if there is store-widening involving different
memory locations, then this is a compiler bug. But the race happens on
a single memory location, in such case the code is buggy.

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