Commit b800c91a authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Linus Torvalds

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 7a3ef208 ("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: default avatarKonstantin Khlebnikov <koct9i@gmail.com>
Reported-and-tested-by: default avatarChris Clayton <chris2553@googlemail.com>
Reported-and-tested-by: default avatarOded Gabbay <oded.gabbay@amd.com>
Reported-and-tested-by: default avatarChih-Wei Huang <cwhuang@android-x86.org>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Acked-by: default avatarVlastimil 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 7a3ef208Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 690eac53
......@@ -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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