Add mutex_lock_killable

Similar to mutex_lock_interruptible, it can be interrupted by a fatal
signal only.

Signed-off-by: Liam R. Howlett <howlett@gmail.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 6014797..05c5903 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -125,15 +125,20 @@
 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
 					unsigned int subclass);
+extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
+					unsigned int subclass);
 
 #define mutex_lock(lock) mutex_lock_nested(lock, 0)
 #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
+#define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
 #else
 extern void fastcall mutex_lock(struct mutex *lock);
 extern int __must_check fastcall mutex_lock_interruptible(struct mutex *lock);
+extern int __must_check fastcall mutex_lock_killable(struct mutex *lock);
 
 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
+# define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
 #endif
 
 /*