linux-kernel - [tip:locking/urgent] futex: Unlock hb-> lock in futex_wait_requeue

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Date:	Fri, 12 Sep 2014 13:10:16 -0700
From:	tip-bot for Thomas Gleixner <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	a.p.zijlstra@...llo.nl, dvhart@...ux.intel.com, davej@...hat.com,
	dave@...olabs.net, tglx@...utronix.de
Subject: [tip:locking/urgent] futex: Unlock hb->
 lock in futex_wait_requeue_pi() error path

Commit-ID:  13c42c2f43b19aab3195f2d357db00d1e885eaa8
Gitweb:     http://git.kernel.org/tip/13c42c2f43b19aab3195f2d357db00d1e885eaa8
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Thu, 11 Sep 2014 23:44:35 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 12 Sep 2014 22:04:36 +0200

futex: Unlock hb->lock in futex_wait_requeue_pi() error path

futex_wait_requeue_pi() calls futex_wait_setup(). If
futex_wait_setup() succeeds it returns with hb->lock held and
preemption disabled. Now the sanity check after this does:

        if (match_futex(&q.key, &key2)) {
	   	ret = -EINVAL;
		goto out_put_keys;
	}

which releases the keys but does not release hb->lock.

So we happily return to user space with hb->lock held and therefor
preemption disabled.

Unlock hb->lock before taking the exit route.

Reported-by: Dave "Trinity" Jones <davej@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Darren Hart <dvhart@...ux.intel.com>
Reviewed-by: Davidlohr Bueso <dave@...olabs.net>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: stable@...r.kernel.org
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1409112318500.4178@nanos
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/futex.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index d3a9d94..815d7af 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2592,6 +2592,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
 	 * shared futexes. We need to compare the keys:
 	 */
 	if (match_futex(&q.key, &key2)) {
+		queue_unlock(hb);
 		ret = -EINVAL;
 		goto out_put_keys;
 	}
--
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