Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1756196Ab0GHLG7 (ORCPT <rfc822;w@1wt.eu>);
	Thu, 8 Jul 2010 07:06:59 -0400
Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:49965 "EHLO
	fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1754323Ab0GHLG6 (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 8 Jul 2010 07:06:58 -0400
X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Peter Zijlstra <peterz@infradead.org>
Subject: Re: FYI: mmap_sem OOM patch
Cc: kosaki.motohiro@jp.fujitsu.com, Michel Lespinasse <walken@google.com>,
       linux-mm <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
       Divyesh Shah <dpshah@google.com>, Ingo Molnar <mingo@elte.hu>
In-Reply-To: <1278586921.1900.67.camel@laptop>
References: <20100708195421.CD48.A69D9226@jp.fujitsu.com> <1278586921.1900.67.camel@laptop>
Message-Id: <20100708200324.CD4B.A69D9226@jp.fujitsu.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit
X-Mailer: Becky! ver. 2.50.07 [ja]
Date: Thu,  8 Jul 2010 20:06:52 +0900 (JST)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1703
Lines: 45

> On Thu, 2010-07-08 at 19:57 +0900, KOSAKI Motohiro wrote:
> > > 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.
> > 
> > Now, I've reread current code. I think mmotm already have this.
> 
> <snip code>
> 
> [ small note on that we really should kill __GFP_NOFAIL, its utter
> deadlock potential ]

I disagree. __GFP_NOFAIL mean this allocation failure can makes really
dangerous result. Instead, OOM-Killer should try to kill next process.
I think.

> > Thought?
> 
> So either its not working or google never tried that code?

Michel?


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/