[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <1346750457-12385-3-git-send-email-walken@google.com>
Date: Tue, 4 Sep 2012 02:20:52 -0700
From: Michel Lespinasse <walken@...gle.com>
To: linux-mm@...ck.org, riel@...hat.com, peterz@...radead.org,
aarcange@...hat.com, hughd@...gle.com, daniel.santos@...ox.com
Cc: linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: [PATCH 2/7] mm: fix potential anon_vma locking issue in mprotect()
This change fixes an anon_vma locking issue in the following situation:
- vma has no anon_vma
- next has an anon_vma
- vma is being shrunk / next is being expanded, due to an mprotect call
We need to take next's anon_vma lock to avoid races with rmap users
(such as page migration) while next is being expanded.
This change also removes an optimization which avoided taking anon_vma
lock during brk adjustments. We could probably make that optimization
work again, but the following anon rmap change would break it,
so I kept things as simple as possible here.
Signed-off-by: Michel Lespinasse <walken@...gle.com>
---
mm/mmap.c | 14 ++++++--------
1 files changed, 6 insertions(+), 8 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index cebc346ba0db..5e64c7dfc090 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -570,14 +570,12 @@ again: remove_next = 1 + (end > next->vm_end);
vma_adjust_trans_huge(vma, start, end, adjust_next);
- /*
- * When changing only vma->vm_end, we don't really need anon_vma
- * lock. This is a fairly rare case by itself, but the anon_vma
- * lock may be shared between many sibling processes. Skipping
- * the lock for brk adjustments makes a difference sometimes.
- */
- if (vma->anon_vma && (importer || start != vma->vm_start)) {
- anon_vma = vma->anon_vma;
+ anon_vma = vma->anon_vma;
+ if (!anon_vma && adjust_next)
+ anon_vma = next->anon_vma;
+ if (anon_vma) {
+ VM_BUG_ON(adjust_next && next->anon_vma &&
+ anon_vma != next->anon_vma);
anon_vma_lock(anon_vma);
}
--
1.7.7.3
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists