futex: Drop refcount if requeue_pi() acquired the rtmutex

Orabug: 23330599

[ Upstream commit fb75a4282d0d9a3c7c44d940582c2d226cf3acfb ]

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@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Darren Hart <darren@dvhart.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Bhuvanesh_Surachari@mentor.com
Cc: Andy Lowe <Andy_Lowe@mentor.com>
Link: http://lkml.kernel.org/r/20151219200607.178132067@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
(cherry picked from commit e70aade221a271f91e2d71901b2d602df2faee15)

Signed-off-by: Dan Duval <dan.duval@oracle.com>

diff --git a/kernel/futex.c b/kernel/futex.c
index 2579e407ff67d039106207f78a466f824e515db6..f3043db6d36f1260920c9aca3cf241389e11c3e7 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2632,6 +2632,11 @@ 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 {