Messages in this thread | | | Date | Mon, 12 Jan 2015 12:21:38 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] mm: fix corner case in anon_vma endless growing prevention |
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On Sun, 11 Jan 2015 16:54:06 +0300 Konstantin Khlebnikov <koct9i@gmail.com> wrote:
> Fix for BUG_ON(anon_vma->degree) splashes in unlink_anon_vmas() > ("kernel BUG at mm/rmap.c:399!"). > > Anon_vma_clone() is usually called for a copy of source vma in destination > argument. If source vma has anon_vma it should be already in dst->anon_vma. > NULL in dst->anon_vma is used as a sign that it's called from anon_vma_fork(). > In this case anon_vma_clone() finds anon_vma for reusing. > > Vma_adjust() calls it differently and this breaks anon_vma reusing logic: > anon_vma_clone() links vma to old anon_vma and updates degree counters but > vma_adjust() overrides vma->anon_vma right after that. As a result final > unlink_anon_vmas() decrements degree for wrong anon_vma. > > This patch assigns ->anon_vma before calling anon_vma_clone(). > > Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com> > Fixes: 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy")
I've asked Greg not to take 7a3ef208e662 into -stable because of this problem. So if you still think we should fix this in -stable, could you please prepare an updated patch and send it to Greg?
> Tested-by: Chris Clayton <chris2553@googlemail.com> > Tested-by: Oded Gabbay <oded.gabbay@amd.com> > Cc: Daniel Forrest <dan.forrest@ssec.wisc.edu> > Cc: Michal Hocko <mhocko@suse.cz> > Cc: Rik van Riel <riel@redhat.com>
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