Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull core locking updates from Ingo Molnar:
 "The main changes are:

   - mutex, completions and rtmutex micro-optimizations
   - lock debugging fix
   - various cleanups in the MCS and the futex code"

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/rtmutex: Optimize setting task running after being blocked
  locking/rwsem: Use task->state helpers
  sched/completion: Add lock-free checking of the blocking case
  sched/completion: Remove unnecessary ->wait.lock serialization when reading completion state
  locking/mutex: Explicitly mark task as running after wakeup
  futex: Fix argument handling in futex_lock_pi() calls
  doc: Fix misnamed FUTEX_CMP_REQUEUE_PI op constants
  locking/Documentation: Update code path
  softirq/preempt: Add missing current->preempt_disable_ip update
  locking/osq: No need for load/acquire when acquire-polling
  locking/mcs: Better differentiate between MCS variants
  locking/mutex: Introduce ww_mutex_set_context_slowpath()
  locking/mutex: Move MCS related comments to proper location
  locking/mutex: Checking the stamp is WW only

1 files changed, 10 insertions, 8 deletions

diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 607f852b4d04..7052d3fd4e7b 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -268,6 +268,15 @@ bool try_wait_for_completion(struct completion *x)
         unsigned long flags;
         int ret = 1;
 
+        /*
+         * Since x->done will need to be locked only
+         * in the non-blocking case, we check x->done
+         * first without taking the lock so we can
+         * return early in the blocking case.
+         */
+        if (!ACCESS_ONCE(x->done))
+                return 0;
+
         spin_lock_irqsave(&x->wait.lock, flags);
         if (!x->done)
                 ret = 0;
@@ -288,13 +297,6 @@ EXPORT_SYMBOL(try_wait_for_completion);
  */
 bool completion_done(struct completion *x)
 {
-        unsigned long flags;
-        int ret = 1;
-
-        spin_lock_irqsave(&x->wait.lock, flags);
-        if (!x->done)
-                ret = 0;
-        spin_unlock_irqrestore(&x->wait.lock, flags);
-        return ret;
+        return !!ACCESS_ONCE(x->done);
 }
 EXPORT_SYMBOL(completion_done);