linux-kernel - Re: FYI: mmap

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Message-ID: <1278586173.1900.50.camel@laptop>
Date:	Thu, 08 Jul 2010 12:49:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	linux-mm <linux-mm@...ck.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Divyesh Shah <dpshah@...gle.com>, Ingo Molnar <mingo@...e.hu>
Subject: Re: FYI: mmap_sem OOM patch

On Thu, 2010-07-08 at 03:39 -0700, Michel Lespinasse wrote:
> 
> 
>         One way to fix this is to have T4 wake from the oom queue and return an
>         allocation failure instead of insisting on going oom itself when T1
>         decides to take down the task.
> 
> How would you have T4 figure out the deadlock situation ? T1 is taking down T2, not T4... 

If T2 and T4 share a mmap_sem they belong to the same process. OOM takes
down the whole process by sending around signals of sorts (SIGKILL?), so
if T4 gets a fatal signal while it is waiting to enter the oom thingy,
have it abort and return an allocation failure.

That alloc failure (along with a pending fatal signal) will very likely
lead to the release of its mmap_sem (if not, there's more things to
cure).

At which point the cycle is broken an stuff continues as it was
intended.
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