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Date: Wed, 6 Jan 2016 08:44:53 -0500
From: Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH v4.4-rc7] sched: move sched lock synchronized bitfields
 in task_struct into ->atomic_flags
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>, Ingo Molnar <mingo@redhat.com>, Sasha Levin <sasha.levin@oracle.com>, Andrew Morton <akpm@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>, cgroups <cgroups@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Vladimir Davydov <vdavydov@parallels.com>, kernel-team <kernel-team@fb.com>, Dmitry Vyukov <dvyukov@google.com>, Peter Zijlstra <peterz@infradead.org>

On Thu, Dec 31, 2015 at 09:56:28PM -0500, Tejun Heo wrote:
> task_struct has a cluster of unsigned bitfields.  Some are updated
> under scheduler locks while others are updated only by the task
> itself.  Currently, the two classes of bitfields aren't distinguished
> and end up on the same word which can lead to clobbering when there
> are simultaneous read-modify-write attempts.  While difficult to prove
> definitely, it's likely that the resulting inconsistency led to low
> frqeuency failures such as wrong memcg_may_oom state or loadavg
> underflow due to clobbered sched_contributes_to_load.

Ping.

-- 
tejun

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