linux-kernel - [tip:core/urgent] futex: Fix locking imbalance

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Message-ID: <tip-bfeed8fcf9970d2c3bcd7950124e77fd49930e36@git.kernel.org>
Date:	Sun, 4 Oct 2009 15:48:40 GMT
From:	tip-bot for Thomas Gleixner <tglx@...utronix.de>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, dvhltc@...ibm.com, hpa@...or.com,
	mingo@...hat.com, a.p.zijlstra@...llo.nl, rercola@....jhu.edu,
	stable@...nel.org, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:core/urgent] futex: Fix locking imbalance

Commit-ID:  bfeed8fcf9970d2c3bcd7950124e77fd49930e36
Gitweb:     http://git.kernel.org/tip/bfeed8fcf9970d2c3bcd7950124e77fd49930e36
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Sun, 4 Oct 2009 09:34:17 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Sun, 4 Oct 2009 17:46:13 +0200

futex: Fix locking imbalance

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@....jhu.edu>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Darren Hart <dvhltc@...ibm.com>
Cc: stable-2.6.31 <stable@...nel.org>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 kernel/futex.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 463af2e..1e176f3 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -916,8 +916,8 @@ 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)) {
 
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