rtmutex-break-out-early-on-first-run.patch

From 78795f419d2e51a3a2d7e41fc8ef419cfe98a8d8 Mon Sep 17 00:00:00 2001
From: Steven Rostedt <srostedt@redhat.com>
Date: Fri, 3 Jul 2009 08:44:23 -0500
Subject: [PATCH] rtmutex: break out early on first run

commit c3c6a61dbff1c6fbbe9a9134e86c2bf19f6671e1 in tip.

Lock stealing and non cmpxchg will always go into the slow path.
This patch detects the fact that we didn't go through the work of
blocking and will exit early.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index f4c5cde..4d53d03 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -768,6 +768,7 @@ rt_spin_lock_slowlock(struct rt_mutex *lock)
 	struct rt_mutex_waiter waiter;
 	unsigned long saved_state, state, flags;
 	struct task_struct *orig_owner;
+	int missed = 0;
 
 	debug_rt_mutex_init_waiter(&waiter);
 	waiter.task = NULL;
@@ -792,8 +793,14 @@ rt_spin_lock_slowlock(struct rt_mutex *lock)
 		int saved_lock_depth = current->lock_depth;
 
 		/* Try to acquire the lock */
-		if (do_try_to_take_rt_mutex(lock, STEAL_LATERAL))
+		if (do_try_to_take_rt_mutex(lock, STEAL_LATERAL)) {
+			/* If we never blocked break out now */
+			if (!missed)
+				goto unlock;
 			break;
+		}
+		missed = 1;
+
 		/*
 		 * waiter.task is NULL the first time we come here and
 		 * when we have been woken up by the previous owner
@@ -850,6 +857,7 @@ rt_spin_lock_slowlock(struct rt_mutex *lock)
 	 */
 	fixup_rt_mutex_waiters(lock);
 
+ unlock:
 	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 
 	debug_rt_mutex_free_waiter(&waiter);
-- 
1.7.1.1