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On 01/11/2015 08:54 AM, Konstantin Khlebnikov 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@xxxxxxxxx> Fixes:
> 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy")
> Tested-by: Chris Clayton <chris2553@xxxxxxxxxxxxxx> Tested-by: Oded
> Gabbay <oded.gabbay@xxxxxxx> Cc: Daniel Forrest
> <dan.forrest@xxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxx> Cc:
> Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
- --
All rights reversed
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