On 01/11/2015 02:54 PM, 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 <[email protected]>
> Fixes: 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy")
> Tested-by: Chris Clayton <[email protected]>
> Tested-by: Oded Gabbay <[email protected]>
> Cc: Daniel Forrest <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Rik van Riel <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
> ---
> mm/mmap.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 7b36aa7..12616c5 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -778,10 +778,12 @@ again: remove_next = 1 + (end >
> next->vm_end);
> if (exporter && exporter->anon_vma && !importer->anon_vma) {
> int error;
>
> + importer->anon_vma = exporter->anon_vma;
> error = anon_vma_clone(importer, exporter);
> - if (error)
> + if (error) {
> + importer->anon_vma = NULL;
> return error;
> - importer->anon_vma = exporter->anon_vma;
> + }
> }
> }
>
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to [email protected]. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"[email protected]";> [email protected] </a>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
