linux-kernel - Re: [PATCH] ksm: fix race between ksmd and exiting task

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Date:	Thu, 2 Jun 2011 14:23:48 -0700
From:	Chris Wright <chrisw@...s-sol.org>
To:	Andrea Righi <andrea@...terlinux.com>
Cc:	Chris Wright <chrisw@...s-sol.org>, CAI Qian <caiqian@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	Izik Eidus <ieidus@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] ksm: fix race between ksmd and exiting task

* Andrea Righi (andrea@...terlinux.com) wrote:
> On Thu, Jun 02, 2011 at 10:35:49AM -0700, Chris Wright wrote:
> > Andrea Righi reported a case where an exiting task can race against
> > ksmd.
> > 
> > ksm_scan.mm_slot == the only registered mm
> > CPU 1 (bug program)		CPU 2 (ksmd)
> >  				list_empty() is false
> > lock
> > ksm_scan.mm_slot
> > list_del
> > unlock
> >  				slot == &ksm_mm_head (but list is now empty_)
> > 
> > Close this race by revalidating that the new slot is not simply the list
> > head again.
> 
> I confirm this fixes the problem on my side.
> 
> Tested-by: Andrea Righi <andrea@...terlinux.com>

Great, thanks for verifying.

thanks,
-chris
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