[patch 10/26] futex: Fix locking imbalance

Greg KH
2009-10-09T23:21:12Z

[-- Attachment #1: futex-fix-locking-imbalance.patch --]
[-- Type: text/plain, Size: 1258 bytes --]

2.6.31-stable review patch. If anyone has any objections, please let us know.

------------------
From: Thomas Gleixner <tglx@linutronix.de>

commit eaaea8036d0261d87d7072c5bc88c7ea730c18ac upstream.

Rich reported a lock imbalance in the futex code:

http://bugzilla.kernel.org/show_bug.cgi?id=14288

It's caused by the displacement of the retry_private label in
futex_wake_op(). The code unlocks the hash bucket locks in the
error handling path and retries without locking them again which
makes the next unlock fail.

Move retry_private so we lock the hash bucket locks when we retry.

Reported-by: Rich Ercolany <rercola@acm.jhu.edu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Darren Hart <dvhltc@us.ibm.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
kernel/futex.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -912,8 +912,8 @@ retry:
hb1 = hash_futex(&key1);
hb2 = hash_futex(&key2);

- double_lock_hb(hb1, hb2);
retry_private:
+ double_lock_hb(hb1, hb2);
op_ret = futex_atomic_op_inuser(op, uaddr2);
if (unlikely(op_ret < 0)) {