linux-kernel - [PATCH 3.16 245/357] futex: Unlock hb->lock in futex_wait_requeue

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Date:	Fri,  3 Oct 2014 14:30:31 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org,
	"=?UTF-8?q?Dave=20 \"Trinity\" =20Jones?=" <davej@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Darren Hart <dvhart@...ux.intel.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: [PATCH 3.16 245/357] futex: Unlock hb->lock in futex_wait_requeue_pi() error path

3.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Thomas Gleixner <tglx@...utronix.de>

commit 13c42c2f43b19aab3195f2d357db00d1e885eaa8 upstream.

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>
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1409112318500.4178@nanos
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2628,6 +2628,7 @@ static int futex_wait_requeue_pi(u32 __u
 	 * 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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