linux-kernel - [PATCH 3.2 18/87] futex: Drop refcount if requeue

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Message-ID: <lsq.1454975631.790407392@decadent.org.uk>
Date:	Mon, 08 Feb 2016 23:53:51 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Andy Lowe" <Andy_Lowe@...tor.com>,
	"Davidlohr Bueso" <dave@...olabs.net>,
	"Darren Hart" <darren@...art.com>,
	"Peter Zijlstra" <peterz@...radead.org>,
	Bhuvanesh_Surachari@...tor.com,
	"Thomas Gleixner" <tglx@...utronix.de>
Subject: [PATCH 3.2 18/87] futex: Drop refcount if requeue_pi() acquired
 the rtmutex

3.2.77-rc1 review patch.  If anyone has any objections, please let me know.

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

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

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: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/futex.c | 5 +++++
 1 file changed, 5 insertions(+)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2492,6 +2492,11 @@ static int futex_wait_requeue_pi(u32 __u
 		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 {