From b800c91a0517071156e772d4fb329ad33590da62 Mon Sep 17 00:00:00 2001
From: Konstantin Khlebnikov <koct9i@gmail.com>
Date: Sun, 11 Jan 2015 16:54:06 +0300
Subject: 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>
---
mm/mmap.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
(limited to 'mm')
diff --git a/mm/mmap.c b/mm/mmap.c
index 0bb74ca2139d..7f684d5a8087 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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