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

Pull core/locking changes from Ingo Molnar:
 "Main changes:

   - another mutex optimization, from Davidlohr Bueso

   - improved lglock lockdep tracking, from Michel Lespinasse

   - [ assorted smaller updates, improvements, cleanups. ]"

* 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  generic-ipi/locking: Fix misleading smp_call_function_any() description
  hung_task debugging: Print more info when reporting the problem
  mutex: Avoid label warning when !CONFIG_MUTEX_SPIN_ON_OWNER
  mutex: Do not unnecessarily deal with waiters
  mutex: Fix/document access-once assumption in mutex_can_spin_on_owner()
  lglock: Update lockdep annotations to report recursive local locks
  lockdep: Introduce lock_acquire_exclusive()/shared() helper macros

1 files changed, 20 insertions, 23 deletions

diff --git a/kernel/mutex.c b/kernel/mutex.c
index a52ee7bb830d..6d647aedffea 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -209,11 +209,13 @@ int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
  */
 static inline int mutex_can_spin_on_owner(struct mutex *lock)
 {
+        struct task_struct *owner;
         int retval = 1;
 
         rcu_read_lock();
-        if (lock->owner)
-                retval = lock->owner->on_cpu;
+        owner = ACCESS_ONCE(lock->owner);
+        if (owner)
+                retval = owner->on_cpu;
         rcu_read_unlock();
         /*
          * if lock->owner is not set, the mutex owner may have just acquired
@@ -461,7 +463,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
                          * performed the optimistic spinning cannot be done.
                          */
                         if (ACCESS_ONCE(ww->ctx))
-                                break;
+                                goto slowpath;
                 }
 
                 /*
@@ -472,7 +474,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
                 owner = ACCESS_ONCE(lock->owner);
                 if (owner && !mutex_spin_on_owner(lock, owner)) {
                         mspin_unlock(MLOCK(lock), &node);
-                        break;
+                        goto slowpath;
                 }
 
                 if ((atomic_read(&lock->count) == 1) &&
@@ -499,7 +501,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
                  * the owner complete.
                  */
                 if (!owner && (need_resched() || rt_task(task)))
-                        break;
+                        goto slowpath;
 
                 /*
                  * The cpu_relax() call is a compiler barrier which forces
@@ -513,6 +515,10 @@ slowpath:
 #endif
         spin_lock_mutex(&lock->wait_lock, flags);
 
+        /* once more, can we acquire the lock? */
+        if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, 0) == 1))
+                goto skip_wait;
+
         debug_mutex_lock_common(lock, &waiter);
         debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
 
@@ -520,9 +526,6 @@ slowpath:
         list_add_tail(&waiter.list, &lock->wait_list);
         waiter.task = task;
 
-        if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, -1) == 1))
-                goto done;
-
         lock_contended(&lock->dep_map, ip);
 
         for (;;) {
@@ -536,7 +539,7 @@ slowpath:
                  * other waiters:
                  */
                 if (MUTEX_SHOW_NO_WAITER(lock) &&
-                   (atomic_xchg(&lock->count, -1) == 1))
+                    (atomic_xchg(&lock->count, -1) == 1))
                         break;
 
                 /*
@@ -561,24 +564,25 @@ slowpath:
                 schedule_preempt_disabled();
                 spin_lock_mutex(&lock->wait_lock, flags);
         }
+        mutex_remove_waiter(lock, &waiter, current_thread_info());
+        /* set it to 0 if there are no waiters left: */
+        if (likely(list_empty(&lock->wait_list)))
+                atomic_set(&lock->count, 0);
+        debug_mutex_free_waiter(&waiter);
 
-done:
+skip_wait:
+        /* got the lock - cleanup and rejoice! */
         lock_acquired(&lock->dep_map, ip);
-        /* got the lock - rejoice! */
-        mutex_remove_waiter(lock, &waiter, current_thread_info());
         mutex_set_owner(lock);
 
         if (!__builtin_constant_p(ww_ctx == NULL)) {
-                struct ww_mutex *ww = container_of(lock,
-                                                      struct ww_mutex,
-                                                      base);
+                struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
                 struct mutex_waiter *cur;
 
                 /*
                  * This branch gets optimized out for the common case,
                  * and is only important for ww_mutex_lock.
                  */
-
                 ww_mutex_lock_acquired(ww, ww_ctx);
                 ww->ctx = ww_ctx;
 
@@ -592,15 +596,8 @@ done:
                 }
         }
 
-        /* set it to 0 if there are no waiters left: */
-        if (likely(list_empty(&lock->wait_list)))
-                atomic_set(&lock->count, 0);
-
         spin_unlock_mutex(&lock->wait_lock, flags);
-
-        debug_mutex_free_waiter(&waiter);
         preempt_enable();
-
         return 0;
 
 err: