[PATCH RT 1/3] rt: Move migrate_disable up in trylocks

[Steven Rostedt]

3.12.15-rt26-rc1 stable review patch.
If anyone has any objections, please let me know.

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

From: Steven Rostedt <rostedt@xxxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxx

Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
Cc: Nicholas Mc Guire <der.herr@xxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: linux-rt-users <linux-rt-users@xxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: John Kacur <jkacur@xxxxxxxxxx>
Cc: Clark Williams <williams@xxxxxxxxxx>
---
 kernel/rt.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

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++;
 }
-- 
1.8.5.3


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