From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nick Piggin <npiggin@suse.de>
Subject: Re: [patch 9/9] mm: fix pagecache write deadlocks
Date: Tue, 6 Feb 2007 06:53:28 +0100
Message-ID: <20070206055328.GD16647@wotan.suse.de>
References: <20070204104609.GA29943@wotan.suse.de> <20070204025602.a5f8c53a.akpm@linux-foundation.org> <20070204110317.GA9034@wotan.suse.de> <20070204031549.203f7b47.akpm@linux-foundation.org> <20070204151051.GB12771@wotan.suse.de> <20070204103620.33c24cad.akpm@linux-foundation.org> <20070206022549.GB31476@wotan.suse.de> <20070206044146.GA11856@wotan.suse.de> <20070205213006.0ea2d918.akpm@linux-foundation.org> <20070206054905.GC16647@wotan.suse.de>
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On Tue, Feb 06, 2007 at 06:49:05AM +0100, Nick Piggin wrote:
> > - If the get_user() doesn't fault, and if we're copying from and to the
> >   same page, we know that we've locked it, so nobody will be able to unmap
> >   it while we're copying from it.
> > 
> > Close, but no cigar!  This is still vulnerable to Hugh's ab/ba deadlock
> > scenario.
> 
> Yes I considered this too. Hard isn't it?

BTW, there are two different abba deadlocks. It's all documented in the
patch 9/9 description.