Add down_timeout and change ACPI to use it

ACPI currently emulates a timeout for semaphores with calls to
down_trylock and sleep.  This produces horrible behaviour in terms of
fairness and excessive wakeups.  Now that we have a unified semaphore
implementation, adding a real down_trylock is almost trivial.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

1 files changed, 35 insertions, 7 deletions

diff --git a/kernel/semaphore.c b/kernel/semaphore.c
index 2da2aed950f..5a12a855898 100644
--- a/kernel/semaphore.c
+++ b/kernel/semaphore.c
@@ -35,6 +35,7 @@
 static noinline void __down(struct semaphore *sem);
 static noinline int __down_interruptible(struct semaphore *sem);
 static noinline int __down_killable(struct semaphore *sem);
+static noinline int __down_timeout(struct semaphore *sem, long jiffies);
 static noinline void __up(struct semaphore *sem);
 
 void down(struct semaphore *sem)
@@ -104,6 +105,20 @@ int down_trylock(struct semaphore *sem)
 }
 EXPORT_SYMBOL(down_trylock);
 
+int down_timeout(struct semaphore *sem, long jiffies)
+{
+        unsigned long flags;
+        int result = 0;
+
+        spin_lock_irqsave(&sem->lock, flags);
+        if (unlikely(sem->count-- <= 0))
+                result = __down_timeout(sem, jiffies);
+        spin_unlock_irqrestore(&sem->lock, flags);
+
+        return result;
+}
+EXPORT_SYMBOL(down_timeout);
+
 void up(struct semaphore *sem)
 {
         unsigned long flags;
@@ -142,10 +157,12 @@ static noinline void __sched __up_down_common(struct semaphore *sem)
 }
 
 /*
- * Because this function is inlined, the 'state' parameter will be constant,
- * and thus optimised away by the compiler.
+ * Because this function is inlined, the 'state' parameter will be
+ * constant, and thus optimised away by the compiler.  Likewise the
+ * 'timeout' parameter for the cases without timeouts.
  */
-static inline int __sched __down_common(struct semaphore *sem, long state)
+static inline int __sched __down_common(struct semaphore *sem, long state,
+                                                                long timeout)
 {
         int result = 0;
         struct task_struct *task = current;
@@ -160,14 +177,20 @@ static inline int __sched __down_common(struct semaphore *sem, long state)
                         goto interrupted;
                 if (state == TASK_KILLABLE && fatal_signal_pending(task))
                         goto interrupted;
+                if (timeout <= 0)
+                        goto timed_out;
                 __set_task_state(task, state);
                 spin_unlock_irq(&sem->lock);
-                schedule();
+                timeout = schedule_timeout(timeout);
                 spin_lock_irq(&sem->lock);
                 if (waiter.up)
                         goto woken;
         }
 
+ timed_out:
+        list_del(&waiter.list);
+        result = -ETIME;
+        goto woken;
  interrupted:
         list_del(&waiter.list);
         result = -EINTR;
@@ -187,17 +210,22 @@ static inline int __sched __down_common(struct semaphore *sem, long state)
 
 static noinline void __sched __down(struct semaphore *sem)
 {
-        __down_common(sem, TASK_UNINTERRUPTIBLE);
+        __down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
 }
 
 static noinline int __sched __down_interruptible(struct semaphore *sem)
 {
-        return __down_common(sem, TASK_INTERRUPTIBLE);
+        return __down_common(sem, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
 }
 
 static noinline int __sched __down_killable(struct semaphore *sem)
 {
-        return __down_common(sem, TASK_KILLABLE);
+        return __down_common(sem, TASK_KILLABLE, MAX_SCHEDULE_TIMEOUT);
+}
+
+static noinline int __sched __down_timeout(struct semaphore *sem, long jiffies)
+{
+        return __down_common(sem, TASK_UNINTERRUPTIBLE, jiffies);
 }
 
 static noinline void __sched __up(struct semaphore *sem)