patches/sched-ttwu-ensure-success-return-is-correct.patch

Subject: sched: ttwu: Return success when only changing the saved_state value
From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 13 Dec 2011 21:42:19 +0100

When a task blocks on a rt lock, it saves the current state in
p->saved_state, so a lock related wake up will not destroy the
original state.

When a real wakeup happens, while the task is running due to a lock
wakeup already, we update p->saved_state to TASK_RUNNING, but we do
not return success, which might cause another wakeup in the waitqueue
code and the task remains in the waitqueue list. Return success in
that case as well.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
---
 kernel/sched/core.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1445,8 +1445,10 @@ try_to_wake_up(struct task_struct *p, un
 		 * if the wakeup condition is true.
 		 */
 		if (!(wake_flags & WF_LOCK_SLEEPER)) {
-			if (p->saved_state & state)
+			if (p->saved_state & state) {
 				p->saved_state = TASK_RUNNING;
+				success = 1;
+			}
 		}
 		goto out;
 	}