linux-kernel - Re: [PATCH 2/7] mm: fix potential anon

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Message-ID: <20120904221641.GL3334@redhat.com>
Date:	Wed, 5 Sep 2012 00:16:41 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	linux-mm@...ck.org, riel@...hat.com, peterz@...radead.org,
	hughd@...gle.com, daniel.santos@...ox.com,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 2/7] mm: fix potential anon_vma locking issue in
 mprotect()

On Tue, Sep 04, 2012 at 02:53:47PM -0700, Michel Lespinasse wrote:
> I think the minimal fix would actually be:
> 
>  	if (vma->anon_vma && (importer || start != vma->vm_start)) {
>  		anon_vma = vma->anon_vma;
> +	else if (next->anon_vma && adjust_next)
> +		anon_vma = next->anon_vma;

Right indeed. The last change required to the above is to check
adjust_next first.

> I suppose if we were to consider adding this fix to the stable series,
> we should probably do it in such a minimal way. I hadn't actually
> considered it, because I was only thinking about this patch series,
> and at patch 4/7 it becomes necessary to lock the anon_vma even if
> only the vm_end side gets modified (so we'd still end up with what I
> proposed in the end)

Ah, that fully explains you removed the optimization :). I was
reviewing the patch as a bugfix for upstream without noticing the
new requirements introduced by the later patches.

I would suggest to do the strict fix as above in as patch 1/8 and push
it in -mm, and to do only the optimization removal in 3/8. I think
we want it in -stable too later, so it'll make life easier to
cherry-pick the commit if it's merged independently.

Thanks!
Andrea
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