| From | lizf@kernel ... | Subject | [PATCH 3.4 099/176] mm: fix corner case in anon_vma endless growing prevention | Date | Thu, 9 Apr 2015 16:45:47 +0800 |
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From: Konstantin Khlebnikov <koct9i@gmail.com>
3.4.107-rc1 review patch. If anyone has any objections, please let me know.
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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> [lizf: Backported to 3.4: define variable @error and return this instead of returning -ENOMEM] Signed-off-by: Zefan Li <lizefan@huawei.com> --- mm/mmap.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c index 84dc5fc..f880ca1 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -567,9 +567,14 @@ 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; + } } } -- 1.9.1
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