[PATCH 4/6] Introduce down_killable()

[Matthew Wilcox <matthew@wil.cx>]

down_killable() is the functional counterpart of mutex_lock_killable.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
---
 include/linux/semaphore.h |    6 ++++++
 kernel/semaphore.c        |   22 ++++++++++++++++++++++
 2 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h
index b3c691b..88f2a28 100644
--- a/include/linux/semaphore.h
+++ b/include/linux/semaphore.h
@@ -62,6 +62,12 @@ 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
  * function may be called from any context, including interrupt and softirq.
diff --git a/kernel/semaphore.c b/kernel/semaphore.c
index d5a7270..2da2aed 100644
--- a/kernel/semaphore.c
+++ b/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)))
-- 
1.5.4.3