Introduce down_killable()

down_killable() is the functional counterpart of mutex_lock_killable.
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

include/linux/semaphore.h

@@ -61,6 +61,12 @@ extern void down(struct semaphore *sem);
  */
 extern int __must_check down_interruptible(struct semaphore *sem);
 
+/*
+ * As down_interruptible(), except the sleep may only be interrupted by
+ * signals which are fatal to this process.
+ */
+extern int __must_check down_killable(struct semaphore *sem);
+
 /*
  * As down(), except this function will not sleep.  It will return 0 if it
  * acquired the semaphore and 1 if the semaphore was contended.  This

kernel/semaphore.c

@@ -34,6 +34,7 @@
 
 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 void __up(struct semaphore *sem);
 
 void down(struct semaphore *sem)
@@ -61,6 +62,20 @@ int down_interruptible(struct semaphore *sem)
 }
 EXPORT_SYMBOL(down_interruptible);
 
+int down_killable(struct semaphore *sem)
+{
+	unsigned long flags;
+	int result = 0;
+
+	spin_lock_irqsave(&sem->lock, flags);
+	if (unlikely(sem->count-- <= 0))
+		result = __down_killable(sem);
+	spin_unlock_irqrestore(&sem->lock, flags);
+
+	return result;
+}
+EXPORT_SYMBOL(down_killable);
+
 /**
  * down_trylock - try to acquire the semaphore, without waiting
  * @sem: the semaphore to be acquired
@@ -143,6 +158,8 @@ static inline int __sched __down_common(struct semaphore *sem, long state)
 	for (;;) {
 		if (state == TASK_INTERRUPTIBLE && signal_pending(task))
 			goto interrupted;
+		if (state == TASK_KILLABLE && fatal_signal_pending(task))
+			goto interrupted;
 		__set_task_state(task, state);
 		spin_unlock_irq(&sem->lock);
 		schedule();
@@ -178,6 +195,11 @@ static noinline int __sched __down_interruptible(struct semaphore *sem)
 	return __down_common(sem, TASK_INTERRUPTIBLE);
 }
 
+static noinline int __sched __down_killable(struct semaphore *sem)
+{
+	return __down_common(sem, TASK_KILLABLE);
+}
+
 static noinline void __sched __up(struct semaphore *sem)
 {
 	if (unlikely(list_empty(&sem->wait_list)))