On 2017-02-13 12:20:52 [+0100], Peter Zijlstra wrote:

quoted

--- a/include/linux/mutex_rt.h
+++ b/include/linux/mutex_rt.h

@@ -43,7 +43,12 @@ extern void __lockfunc _mutex_unlock(str
 #define mutex_lock_killable(l)		_mutex_lock_killable(l)
 #define mutex_trylock(l)		_mutex_trylock(l)
 #define mutex_unlock(l)			_mutex_unlock(l)
+
+#ifdef CONFIG_DEBUG_MUTEXES
 #define mutex_destroy(l)		rt_mutex_destroy(&(l)->lock)
+#else
+static inline void mutex_destroy(struct mutex *lock) {}
+#endif
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # define mutex_lock_nested(l, s)	_mutex_lock_nested(l, s)
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c

@@ -2027,8 +2027,7 @@ void rt_mutex_destroy(struct rt_mutex *l
 	lock->magic = NULL;
 #endif
 }
-
-EXPORT_SYMBOL_GPL(rt_mutex_destroy);
+EXPORT_SYMBOL(rt_mutex_destroy);

I don't understand:

$ git grep "EXPORT_SYMBOL.*mutex_destroy"
kernel/locking/mutex-debug.c:EXPORT_SYMBOL_GPL(mutex_destroy);
kernel/locking/rtmutex.c:EXPORT_SYMBOL_GPL(rt_mutex_destroy);

Your proposed patch makes it different from mainline.

as discussed off-list, I will drop that _GPL removal hunk and keep only
the (first) inline hunk.
!GPL users should compile with !CONFIG_DEBUG_MUTEXES and
!CONFIG_DEBUG_RT_MUTEXES so there should be no regression.

Sebastian