linux-kernel - [PATCH 3.2 045/102] futex: Unlock hb->lock in futex_wait_requeue

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Date:	Sat, 01 Nov 2014 22:28:03 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Dave " Trinity " Jones" <davej@...hat.com>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	"Davidlohr Bueso" <dave@...olabs.net>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Darren Hart" <dvhart@...ux.intel.com>
Subject: [PATCH 3.2 045/102] futex: Unlock hb->lock in futex_wait_requeue_pi()
 error path

3.2.64-rc1 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>
[bwh: Backported to 3.2: queue_unlock() takes two parameters]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/futex.c | 1 +
 1 file changed, 1 insertion(+)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2460,6 +2460,7 @@ static int futex_wait_requeue_pi(u32 __u
 	 * shared futexes. We need to compare the keys:
 	 */
 	if (match_futex(&q.key, &key2)) {
+		queue_unlock(&q, hb);
 		ret = -EINVAL;
 		goto out_put_keys;
 	}

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