From 61b4dcfedfffa3f36c3fd76fb414c67b5e3c960d Mon Sep 17 00:00:00 2001
From: Steven Rostedt <rostedt@goodmis.org>
Date: Tue, 29 Apr 2014 20:13:08 -0400
Subject: rt: Move migrate_disable up in trylocks

The changes to move the migrate_disable() down in the trylocks()
caused race conditions to appear in the cpu hotplug code. The
migrate disables must be done before any of the rtmutexes are
taken, otherwise a lock may be held that prevents hotplug from
moving forward.

Link: http://lkml.kernel.org/r/20140429201308.63292691@gandalf.local.home

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Nicholas Mc Guire <der.herr@hofr.at>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-rt-users <linux-rt-users@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Kacur <jkacur@redhat.com>
Cc: Clark Williams <williams@redhat.com>

diff --git a/kernel/rt.c b/kernel/rt.c
index 5d17727..5f44def 100644
--- a/kernel/rt.c
+++ b/kernel/rt.c
@@ -180,12 +180,15 @@ EXPORT_SYMBOL(_mutex_unlock);
  */
 int __lockfunc rt_write_trylock(rwlock_t *rwlock)
 {
-	int ret = rt_mutex_trylock(&rwlock->lock);
+	int ret;
+
+	migrate_disable();
+	ret = rt_mutex_trylock(&rwlock->lock);
 
-	if (ret) {
+	if (ret)
 		rwlock_acquire(&rwlock->dep_map, 0, 1, _RET_IP_);
-		migrate_disable();
-	}
+	else
+		migrate_enable();
 
 	return ret;
 }
@@ -212,11 +215,12 @@ int __lockfunc rt_read_trylock(rwlock_t *rwlock)
 	 * write locked.
 	 */
 	if (rt_mutex_owner(lock) != current) {
+		migrate_disable();
 		ret = rt_mutex_trylock(lock);
-		if (ret) {
+		if (ret)
 			rwlock_acquire(&rwlock->dep_map, 0, 1, _RET_IP_);
-			migrate_disable();
-		}
+		else
+			migrate_enable();
 	} else if (!rwlock->read_depth) {
 		ret = 0;
 	}
@@ -245,8 +249,8 @@ void __lockfunc rt_read_lock(rwlock_t *rwlock)
 	 */
 	if (rt_mutex_owner(lock) != current) {
 		rwlock_acquire(&rwlock->dep_map, 0, 0, _RET_IP_);
-		__rt_spin_lock(lock);
 		migrate_disable();
+		__rt_spin_lock(lock);
 	}
 	rwlock->read_depth++;
 }
-- 
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