linux-kernel - Re: [PATCH] mm, oom: Fix race when selecting process to kill

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Message-ID: <CAA25o9QG2BOmV5MoXCH73sadKoRD6wPivKq6TLvEem8GhZeXGg@mail.gmail.com>
Date:	Tue, 5 Nov 2013 20:45:07 -0800
From:	Luigi Semenzato <semenzato@...gle.com>
To:	Sameer Nanda <snanda@...omium.org>, msb@...ebook.com
Cc:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>, mhocko@...e.cz,
	Johannes Weiner <hannes@...xchg.org>,
	Rusty Russell <rusty@...tcorp.com.au>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, oom: Fix race when selecting process to kill

It's interesting that this was known for 3+ years, but nobody bothered
adding a small warning to the code.

We noticed this because it's actually happening on Chromebooks in the
field.  We try to minimize OOM kills, but we can deal with them.  Of
course, a hung kernel we cannot deal with.

On Tue, Nov 5, 2013 at 7:04 PM, Sameer Nanda <snanda@...omium.org> wrote:
>
>
>
> On Tue, Nov 5, 2013 at 5:27 PM, David Rientjes <rientjes@...gle.com> wrote:
>>
>> On Tue, 5 Nov 2013, Luigi Semenzato wrote:
>>
>> > It's not enough to hold a reference to the task struct, because it can
>> > still be taken out of the circular list of threads.  The RCU
>> > assumptions don't hold in that case.
>> >
>>
>> Could you please post a proper bug report that isolates this at the cause?
>
>
> We've been running into this issue on Chrome OS. crbug.com/256326 has
> additional
> details.  The issue manifests itself as a soft lockup.
>
> The kernel we've been seeing this on is 3.8.
>
> We have a pretty consistent repro currently.  Happy to try out other
> suggestions
> for a fix.
>
>>
>>
>> Thanks.
>
>
>
>
> --
> Sameer
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