linux-kernel - [tip:locking/core] futex: Drop refcount if requeue

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Message-ID: <tip-fb75a4282d0d9a3c7c44d940582c2d226cf3acfb@git.kernel.org>
Date:	Sun, 20 Dec 2015 05:18:39 -0800
From:	tip-bot for Thomas Gleixner <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	Andy_Lowe@...tor.com, tglx@...utronix.de, hpa@...or.com,
	linux-kernel@...r.kernel.org, darren@...art.com, dave@...olabs.net,
	peterz@...radead.org, mingo@...nel.org
Subject: [tip:locking/core] futex: Drop refcount if requeue_pi()
  acquired the rtmutex

Commit-ID:  fb75a4282d0d9a3c7c44d940582c2d226cf3acfb
Gitweb:     http://git.kernel.org/tip/fb75a4282d0d9a3c7c44d940582c2d226cf3acfb
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Sat, 19 Dec 2015 20:07:38 +0000
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Sun, 20 Dec 2015 12:43:24 +0100

futex: Drop refcount if requeue_pi() acquired the rtmutex

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>
Cc: stable@...r.kernel.org
---
 kernel/futex.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index 684d754..24fbc77 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2755,6 +2755,11 @@ 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 {
--
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