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authorThomas Gleixner <tglx@linutronix.de>2014-06-10 22:53:40 +0200
committerThomas Gleixner <tglx@linutronix.de>2014-06-21 22:05:30 +0200
commit88f2b4c15e561bb5c28709d666364f273bf54b98 (patch)
tree7afc35714df46561b18b78bb39e70d7cbaafabe3 /kernel/locking
parentfddeca638ed428d447d60fc0942a094814073cc6 (diff)
rtmutex: Simplify rtmutex_slowtrylock()
Oleg noticed that rtmutex_slowtrylock() has a pointless check for rt_mutex_owner(lock) != current. To avoid calling try_to_take_rtmutex() we really want to check whether the lock has an owner at all or whether the trylock failed because the owner is NULL, but the RT_MUTEX_HAS_WAITERS bit is set. This covers the lock is owned by caller situation as well. We can actually do this check lockless. trylock is taking a chance whether we take lock->wait_lock to do the check or not. Add comments to the function while at it. Reported-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/rtmutex.c31
1 files changed, 20 insertions, 11 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index fc605941b9b8..50bc93b3552f 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -960,22 +960,31 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
/*
* Slow path try-lock function:
*/
-static inline int
-rt_mutex_slowtrylock(struct rt_mutex *lock)
+static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
{
- int ret = 0;
+ int ret;
+
+ /*
+ * If the lock already has an owner we fail to get the lock.
+ * This can be done without taking the @lock->wait_lock as
+ * it is only being read, and this is a trylock anyway.
+ */
+ if (rt_mutex_owner(lock))
+ return 0;
+ /*
+ * The mutex has currently no owner. Lock the wait lock and
+ * try to acquire the lock.
+ */
raw_spin_lock(&lock->wait_lock);
- if (likely(rt_mutex_owner(lock) != current)) {
+ ret = try_to_take_rt_mutex(lock, current, NULL);
- ret = try_to_take_rt_mutex(lock, current, NULL);
- /*
- * try_to_take_rt_mutex() sets the lock waiters
- * bit unconditionally. Clean this up.
- */
- fixup_rt_mutex_waiters(lock);
- }
+ /*
+ * try_to_take_rt_mutex() sets the lock waiters bit
+ * unconditionally. Clean this up.
+ */
+ fixup_rt_mutex_waiters(lock);
raw_spin_unlock(&lock->wait_lock);