linux-kernel - [PATCH 3.12 139/142] futex: Drop refcount if requeue

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Message-Id: <5dfda55780189a40f546d994cb0fcae788805d01.1456308281.git.jslaby@suse.cz>
Date:	Wed, 24 Feb 2016 11:05:34 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Darren Hart <darren@...art.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Bhuvanesh_Surachari@...tor.com, Andy Lowe <Andy_Lowe@...tor.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 139/142] futex: Drop refcount if requeue_pi() acquired the rtmutex

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

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

===============

commit fb75a4282d0d9a3c7c44d940582c2d226cf3acfb upstream.

If the proxy lock in the requeue loop acquires the rtmutex for a
waiter then it acquired also refcount on the pi_state related to the
futex, but the waiter side does not drop the reference count.

Add the missing free_pi_state() call.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Darren Hart <darren@...art.com>
Cc: Davidlohr Bueso <dave@...olabs.net>
Cc: Bhuvanesh_Surachari@...tor.com
Cc: Andy Lowe <Andy_Lowe@...tor.com>
Link: http://lkml.kernel.org/r/20151219200607.178132067@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 kernel/futex.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index 3ee1b3ce78df..509bdd404414 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2497,6 +2497,11 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
 		if (q.pi_state && (q.pi_state->owner != current)) {
 			spin_lock(q.lock_ptr);
 			ret = fixup_pi_state_owner(uaddr2, &q, current);
+			/*
+			 * Drop the reference to the pi state which
+			 * the requeue_pi() code acquired for us.
+			 */
+			free_pi_state(q.pi_state);
 			spin_unlock(q.lock_ptr);
 		}
 	} else {
-- 
2.7.1