[PATCH 4.9 91/93] futex: Add missing error handling to FUTEX_REQUEUE_PI

[Greg Kroah-Hartman]

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

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

From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

commit 9bbb25afeb182502ca4f2c4f3f88af0681b34cae upstream.

Thomas spotted that fixup_pi_state_owner() can return errors and we
fail to unlock the rt_mutex in that case.

Reported-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Darren Hart <dvhart@xxxxxxxxxxxxxxx>
Cc: juri.lelli@xxxxxxx
Cc: bigeasy@xxxxxxxxxxxxx
Cc: xlpang@xxxxxxxxxx
Cc: rostedt@xxxxxxxxxxx
Cc: mathieu.desnoyers@xxxxxxxxxxxx
Cc: jdesfossez@xxxxxxxxxxxx
Cc: dvhart@xxxxxxxxxxxxx
Cc: bristot@xxxxxxxxxx
Link: http://lkml.kernel.org/r/20170304093558.867401760@xxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/futex.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2896,6 +2896,8 @@ 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);
+			if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current)
+				rt_mutex_unlock(&q.pi_state->pi_mutex);
 			/*
 			 * Drop the reference to the pi state which
 			 * the requeue_pi() code acquired for us.