rtmutex-Rearrange-the-code.patch

From 7c3df123e248a20ae083d51e720c415d52b092c9 Mon Sep 17 00:00:00 2001
From: Gregory Haskins <ghaskins@novell.com>
Date: Fri, 3 Jul 2009 08:44:20 -0500
Subject: [PATCH] rtmutex: Rearrange the code

commit 090e2db9b77d03d264b0a12048448ae49a907e0c in tip.

The current logic makes rather coarse adjustments to current->state since
it is planning on sleeping anyway.  We want to eventually move to an
adaptive (e.g. optional sleep) algorithm, so we tighten the scope of the
adjustments to bracket the schedule().  This should yield correct behavior
with or without the adaptive features that are added later in the series.
We add it here as a separate patch for greater review clarity on smaller
changes.

Signed-off-by: Gregory Haskins <ghaskins@novell.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 3a4e820..543e43c 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -656,6 +656,14 @@ rt_spin_lock_fastunlock(struct rt_mutex *lock,
 		slowfn(lock);
 }
 
+static inline void
+update_current(unsigned long new_state, unsigned long *saved_state)
+{
+	unsigned long state = xchg(&current->state, new_state);
+	if (unlikely(state == TASK_RUNNING))
+		*saved_state = TASK_RUNNING;
+}
+
 /*
  * Slow path lock function spin_lock style: this variant is very
  * careful not to miss any non-lock wakeups.
@@ -695,7 +703,7 @@ rt_spin_lock_slowlock(struct rt_mutex *lock)
 	 * saved_state accordingly. If we did not get a real wakeup
 	 * then we return with the saved state.
 	 */
-	saved_state = xchg(&current->state, TASK_UNINTERRUPTIBLE);
+	saved_state = current->state;
 
 	for (;;) {
 		int saved_lock_depth = current->lock_depth;
@@ -725,13 +733,14 @@ rt_spin_lock_slowlock(struct rt_mutex *lock)
 
 		debug_rt_mutex_print_deadlock(&waiter);
 
-		schedule_rt_mutex(lock);
+		update_current(TASK_UNINTERRUPTIBLE, &saved_state);
+		if (waiter.task)
+			schedule_rt_mutex(lock);
+		else
+			update_current(TASK_RUNNING_MUTEX, &saved_state);
 
 		raw_spin_lock_irqsave(&lock->wait_lock, flags);
 		current->lock_depth = saved_lock_depth;
-		state = xchg(&current->state, TASK_UNINTERRUPTIBLE);
-		if (unlikely(state == TASK_RUNNING))
-			saved_state = TASK_RUNNING;
 	}
 
 	state = xchg(&current->state, saved_state);
-- 
1.7.1.1