mutex_lock_interruptible(): add __must_check

It's not sane to use mutex_lock_interruptible() and to then ignore the result.

Ditto down_interruptible(), but I'm lazy.

Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mutex.h

@@ -121,11 +121,12 @@ static inline int fastcall mutex_is_locked(struct mutex *lock)
  * Also see Documentation/mutex-design.txt.
  */
 extern void fastcall mutex_lock(struct mutex *lock);
-extern int fastcall mutex_lock_interruptible(struct mutex *lock);
+extern int __must_check fastcall mutex_lock_interruptible(struct mutex *lock);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
-extern int mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass);
+extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
+					unsigned int subclass);
 #else
 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)