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Subject[PATCH RT 1/3] rt: Move migrate_disable up in trylocks
3.12.15-rt26-rc1 stable review patch.
If anyone has any objections, please let me know.

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

From: Steven Rostedt <rostedt@goodmis.org>

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>
---
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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