linux-kernel - Re: [PATCH 08 of 11] anon-vma-rwsem

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Date:	Wed, 7 May 2008 19:52:56 -0500
From:	Robin Holt <holt@....com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Christoph Lameter <clameter@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <andrea@...ranet.com>, steiner@....com,
	holt@....com, npiggin@...e.de, a.p.zijlstra@...llo.nl,
	kvm-devel@...ts.sourceforge.net, kanojsarcar@...oo.com,
	rdreier@...co.com, swise@...ngridcomputing.com,
	linux-kernel@...r.kernel.org, avi@...ranet.com, linux-mm@...ck.org,
	general@...ts.openfabrics.org, hugh@...itas.com,
	rusty@...tcorp.com.au, aliguori@...ibm.com, chrisw@...hat.com,
	marcelo@...ck.org, dada1@...mosbay.com, paulmck@...ibm.com
Subject: Re: [PATCH 08 of 11] anon-vma-rwsem

On Wed, May 07, 2008 at 05:03:30PM -0700, Linus Torvalds wrote:
> 
> 
> On Wed, 7 May 2008, Christoph Lameter wrote:
> > 
> > Multiple vmas may share the same mapping or refer to the same anonymous 
> > vma. The above code will deadlock since we may take some locks multiple 
> > times.
> 
> Ok, so that actually _is_ a problem. It would be easy enough to also add 
> just a flag to the vma (VM_MULTILOCKED), which is still cleaner than doing 
> a vmalloc and a whole sort thing, but if this is really rare, maybe Ben's 
> suggestion of just using stop-machine is actually the right one just 
> because it's _so_ simple.

Also, stop-machine will not work if we come to the conclusion that
i_mmap_lock and anon_vma->lock need to be sleepable locks.

Thanks,
Robin Holt
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