Messages in this thread Patch in this message | | | Subject | [PATCH] mm: fix corner case in anon_vma endless growing prevention | From | Konstantin Khlebnikov <> | Date | Sun, 11 Jan 2015 16:54:06 +0300 |
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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") 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> --- 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; + } } }
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