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authorKonstantin Khlebnikov <koct9i@gmail.com>2015-01-11 16:54:06 +0300
committerBen Hutchings <ben@decadent.org.uk>2015-02-20 00:49:36 +0000
commit36323bf0f2f903867d705d8c8bd956a06a5a7be4 (patch)
treed3fc8fece6efa2757d6d59e442f57c9f3d778d47 /mm
parented19644d090c3e2162d5488594336ec43da23d38 (diff)
mm: fix corner case in anon_vma endless growing prevention
commit b800c91a0517071156e772d4fb329ad33590da62 upstream. 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> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> [bwh: Backported to 3.2: vma_adjust() didn't use a variable to propagate the error code from anon_vma_clone(); change that at the same time] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'mm')
-rw-r--r--mm/mmap.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index a3446759fe8e..13b5685db36d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -537,9 +537,14 @@ again: remove_next = 1 + (end > next->vm_end);
* shrinking vma had, to cover any anon pages imported.
*/
if (exporter && exporter->anon_vma && !importer->anon_vma) {
- if (anon_vma_clone(importer, exporter))
- return -ENOMEM;
+ int error;
+
importer->anon_vma = exporter->anon_vma;
+ error = anon_vma_clone(importer, exporter);
+ if (error) {
+ importer->anon_vma = NULL;
+ return error;
+ }
}
}