From: Andrew Morton <akpm@linux-foundation.org>
To: Michel Lespinasse <walken@google.com>
Cc: linux-mm@kvack.org, aarcange@redhat.com
Subject: Re: [PATCH] mm: fix potential anon_vma locking issue in mprotect()
Date: Tue, 4 Sep 2012 16:46:36 -0700 [thread overview]
Message-ID: <20120904164636.158d8012.akpm@linux-foundation.org> (raw)
In-Reply-To: <1346801989-18274-1-git-send-email-walken@google.com>
On Tue, 4 Sep 2012 16:39:49 -0700
Michel Lespinasse <walken@google.com> wrote:
> This change fixes an anon_vma locking issue in the following situation:
> - vma has no anon_vma
> - next has an anon_vma
> - vma is being shrunk / next is being expanded, due to an mprotect call
>
> We need to take next's anon_vma lock to avoid races with rmap users
> (such as page migration) while next is being expanded.
>
> ...
>
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -578,8 +578,12 @@ again: remove_next = 1 + (end > next->vm_end);
> */
> if (vma->anon_vma && (importer || start != vma->vm_start)) {
> anon_vma = vma->anon_vma;
> + VM_BUG_ON(adjust_next && next->anon_vma &&
> + anon_vma != next->anon_vma);
> + } else if (adjust_next && next->anon_vma)
> + anon_vma = next->anon_vma;
> + if (anon_vma)
> anon_vma_lock(anon_vma);
> - }
>
> if (root) {
> flush_dcache_mmap_lock(mapping);
hm, OK. How serious was that bug? I'm suspecting "only needed in
3.7".
If we want to fix this in 3.6 and perhaps -stable, I'm a bit worried
about that new VM_BUG_ON(). Not that I don't trust you or anything,
but these things tend to go bang when people least expected it.
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next prev parent reply other threads:[~2012-09-04 23:46 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-04 23:39 [PATCH] mm: fix potential anon_vma locking issue in mprotect() Michel Lespinasse
2012-09-04 23:45 ` Andrea Arcangeli
2012-09-04 23:46 ` Andrew Morton [this message]
2012-09-05 0:02 ` Michel Lespinasse
2012-09-05 10:11 ` Andrea Arcangeli
2012-09-05 19:24 ` Hugh Dickins
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