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>
diff --git a/kernel/semaphore.c b/kernel/semaphore.c
index 2da2aed..5a12a85 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 @@
}
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 @@
}
/*
- * 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 @@
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 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)
