maple_tree: relax lockdep checks for on-stack trees

To support early release of the maple tree locks, do not lockdep check the
lock if it is set to NULL.  This is intended for the special case on-stack
use of tracking entries and not for general use.

Link: https://lkml.kernel.org/r/20230714195551.894800-3-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oliver Sang <oliver.sang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/maple_tree.h

@@ -182,7 +182,9 @@ enum maple_type {
 
 #ifdef CONFIG_LOCKDEP
 typedef struct lockdep_map *lockdep_map_p;
-#define mt_lock_is_held(mt)	lock_is_held(mt->ma_external_lock)
+#define mt_lock_is_held(mt)                                             \
+	(!(mt)->ma_external_lock || lock_is_held((mt)->ma_external_lock))
+
 #define mt_set_external_lock(mt, lock)					\
 	(mt)->ma_external_lock = &(lock)->dep_map
 #else