1 files changed, 104 insertions, 17 deletions

diff --git a/kernel/mutex.c b/kernel/mutex.c
index 4f45d4b658ef..5d79781394a3 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -10,6 +10,11 @@
  * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
  * David Howells for suggestions and improvements.
  *
+ *  - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline
+ *    from the -rt tree, where it was originally implemented for rtmutexes
+ *    by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale
+ *    and Sven Dietrich.
+ *
  * Also see Documentation/mutex-design.txt.
  */
 #include <linux/mutex.h>
@@ -46,6 +51,7 @@ __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
         atomic_set(&lock->count, 1);
         spin_lock_init(&lock->wait_lock);
         INIT_LIST_HEAD(&lock->wait_list);
+        mutex_clear_owner(lock);
 
         debug_mutex_init(lock, name, key);
 }
@@ -91,6 +97,7 @@ void inline __sched mutex_lock(struct mutex *lock)
          * 'unlocked' into 'locked' state.
          */
         __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
+        mutex_set_owner(lock);
 }
 
 EXPORT_SYMBOL(mutex_lock);
@@ -115,6 +122,14 @@ void __sched mutex_unlock(struct mutex *lock)
          * The unlocking fastpath is the 0->1 transition from 'locked'
          * into 'unlocked' state:
          */
+#ifndef CONFIG_DEBUG_MUTEXES
+        /*
+         * When debugging is enabled we must not clear the owner before time,
+         * the slow path will always be taken, and that clears the owner field
+         * after verifying that it was indeed current.
+         */
+        mutex_clear_owner(lock);
+#endif
         __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
 }
 
@@ -129,21 +144,75 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 {
         struct task_struct *task = current;
         struct mutex_waiter waiter;
-        unsigned int old_val;
         unsigned long flags;
 
+        preempt_disable();
+        mutex_acquire(&lock->dep_map, subclass, 0, ip);
+#if defined(CONFIG_SMP) && !defined(CONFIG_DEBUG_MUTEXES)
+        /*
+         * Optimistic spinning.
+         *
+         * We try to spin for acquisition when we find that there are no
+         * pending waiters and the lock owner is currently running on a
+         * (different) CPU.
+         *
+         * The rationale is that if the lock owner is running, it is likely to
+         * release the lock soon.
+         *
+         * Since this needs the lock owner, and this mutex implementation
+         * doesn't track the owner atomically in the lock field, we need to
+         * track it non-atomically.
+         *
+         * We can't do this for DEBUG_MUTEXES because that relies on wait_lock
+         * to serialize everything.
+         */
+
+        for (;;) {
+                struct thread_info *owner;
+
+                /*
+                 * If there's an owner, wait for it to either
+                 * release the lock or go to sleep.
+                 */
+                owner = ACCESS_ONCE(lock->owner);
+                if (owner && !mutex_spin_on_owner(lock, owner))
+                        break;
+
+                if (atomic_cmpxchg(&lock->count, 1, 0) == 1) {
+                        lock_acquired(&lock->dep_map, ip);
+                        mutex_set_owner(lock);
+                        preempt_enable();
+                        return 0;
+                }
+
+                /*
+                 * When there's no owner, we might have preempted between the
+                 * owner acquiring the lock and setting the owner field. If
+                 * we're an RT task that will live-lock because we won't let
+                 * the owner complete.
+                 */
+                if (!owner && (need_resched() || rt_task(task)))
+                        break;
+
+                /*
+                 * The cpu_relax() call is a compiler barrier which forces
+                 * everything in this loop to be re-loaded. We don't need
+                 * memory barriers as we'll eventually observe the right
+                 * values at the cost of a few extra spins.
+                 */
+                cpu_relax();
+        }
+#endif
         spin_lock_mutex(&lock->wait_lock, flags);
 
         debug_mutex_lock_common(lock, &waiter);
-        mutex_acquire(&lock->dep_map, subclass, 0, ip);
         debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
 
         /* add waiting tasks to the end of the waitqueue (FIFO): */
         list_add_tail(&waiter.list, &lock->wait_list);
         waiter.task = task;
 
-        old_val = atomic_xchg(&lock->count, -1);
-        if (old_val == 1)
+        if (atomic_xchg(&lock->count, -1) == 1)
                 goto done;
 
         lock_contended(&lock->dep_map, ip);
@@ -158,8 +227,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
                  * that when we release the lock, we properly wake up the
                  * other waiters:
                  */
-                old_val = atomic_xchg(&lock->count, -1);
-                if (old_val == 1)
+                if (atomic_xchg(&lock->count, -1) == 1)
                         break;
 
                 /*
@@ -173,21 +241,22 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
                         spin_unlock_mutex(&lock->wait_lock, flags);
 
                         debug_mutex_free_waiter(&waiter);
+                        preempt_enable();
                         return -EINTR;
                 }
                 __set_task_state(task, state);
 
                 /* didnt get the lock, go to sleep: */
                 spin_unlock_mutex(&lock->wait_lock, flags);
-                schedule();
+                __schedule();
                 spin_lock_mutex(&lock->wait_lock, flags);
         }
 
 done:
         lock_acquired(&lock->dep_map, ip);
         /* got the lock - rejoice! */
-        mutex_remove_waiter(lock, &waiter, task_thread_info(task));
-        debug_mutex_set_owner(lock, task_thread_info(task));
+        mutex_remove_waiter(lock, &waiter, current_thread_info());
+        mutex_set_owner(lock);
 
         /* set it to 0 if there are no waiters left: */
         if (likely(list_empty(&lock->wait_list)))
@@ -196,6 +265,7 @@ done:
         spin_unlock_mutex(&lock->wait_lock, flags);
 
         debug_mutex_free_waiter(&waiter);
+        preempt_enable();
 
         return 0;
 }
@@ -222,7 +292,8 @@ int __sched
 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
 {
         might_sleep();
-        return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass, _RET_IP_);
+        return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
+                                   subclass, _RET_IP_);
 }
 
 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
@@ -260,8 +331,6 @@ __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
                 wake_up_process(waiter->task);
         }
 
-        debug_mutex_clear_owner(lock);
-
         spin_unlock_mutex(&lock->wait_lock, flags);
 }
 
@@ -298,18 +367,30 @@ __mutex_lock_interruptible_slowpath(atomic_t *lock_count);
  */
 int __sched mutex_lock_interruptible(struct mutex *lock)
 {
+        int ret;
+
         might_sleep();
-        return __mutex_fastpath_lock_retval
+        ret =  __mutex_fastpath_lock_retval
                         (&lock->count, __mutex_lock_interruptible_slowpath);
+        if (!ret)
+                mutex_set_owner(lock);
+
+        return ret;
 }
 
 EXPORT_SYMBOL(mutex_lock_interruptible);
 
 int __sched mutex_lock_killable(struct mutex *lock)
 {
+        int ret;
+
         might_sleep();
-        return __mutex_fastpath_lock_retval
+        ret = __mutex_fastpath_lock_retval
                         (&lock->count, __mutex_lock_killable_slowpath);
+        if (!ret)
+                mutex_set_owner(lock);
+
+        return ret;
 }
 EXPORT_SYMBOL(mutex_lock_killable);
 
@@ -352,9 +433,10 @@ static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
 
         prev = atomic_xchg(&lock->count, -1);
         if (likely(prev == 1)) {
-                debug_mutex_set_owner(lock, current_thread_info());
+                mutex_set_owner(lock);
                 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
         }
+
         /* Set it back to 0 if there are no waiters: */
         if (likely(list_empty(&lock->wait_list)))
                 atomic_set(&lock->count, 0);
@@ -380,8 +462,13 @@ static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
  */
 int __sched mutex_trylock(struct mutex *lock)
 {
-        return __mutex_fastpath_trylock(&lock->count,
-                                        __mutex_trylock_slowpath);
+        int ret;
+
+        ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath);
+        if (ret)
+                mutex_set_owner(lock);
+
+        return ret;
 }
 
 EXPORT_SYMBOL(mutex_trylock);