Commit b800c91a0517071156e772d4fb329ad33590da62
Committed by
Linus Torvalds
1 parent
690eac53da
Exists in
ti-lsk-linux-4.1.y
and in
10 other branches
mm: fix corner case in anon_vma endless growing prevention
Fix for BUG_ON(anon_vma->degree) splashes in unlink_anon_vmas() ("kernel BUG at mm/rmap.c:399!") caused by commit 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy") 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> Reported-and-tested-by: Chris Clayton <chris2553@googlemail.com> Reported-and-tested-by: Oded Gabbay <oded.gabbay@amd.com> Reported-and-tested-by: Chih-Wei Huang <cwhuang@android-x86.org> Acked-by: Rik van Riel <riel@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Daniel Forrest <dan.forrest@ssec.wisc.edu> Cc: Michal Hocko <mhocko@suse.cz> Cc: stable@vger.kernel.org # to match back-porting of 7a3ef208e662 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Showing 1 changed file with 4 additions and 2 deletions Side-by-side Diff
mm/mmap.c
... | ... | @@ -778,10 +778,12 @@ |
778 | 778 | if (exporter && exporter->anon_vma && !importer->anon_vma) { |
779 | 779 | int error; |
780 | 780 | |
781 | + importer->anon_vma = exporter->anon_vma; | |
781 | 782 | error = anon_vma_clone(importer, exporter); |
782 | - if (error) | |
783 | + if (error) { | |
784 | + importer->anon_vma = NULL; | |
783 | 785 | return error; |
784 | - importer->anon_vma = exporter->anon_vma; | |
786 | + } | |
785 | 787 | } |
786 | 788 | } |
787 | 789 |