maple_tree: change RCU checks to WARN_ON() instead of BUG_ON()

If RCU is enabled and the tree isn't locked, just warn the user and avoid
crashing the kernel.

Link: https://lkml.kernel.org/r/20230518145544.1722059-9-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: David Binderman <dcb314@hotmail.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Vernon Yang <vernon2gm@gmail.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/maple_tree.h

@@ -616,7 +616,7 @@ static inline void mt_clear_in_rcu(struct maple_tree *mt)
 		return;
 
 	if (mt_external_lock(mt)) {
-		BUG_ON(!mt_lock_is_held(mt));
+		WARN_ON(!mt_lock_is_held(mt));
 		mt->ma_flags &= ~MT_FLAGS_USE_RCU;
 	} else {
 		mtree_lock(mt);
@@ -635,7 +635,7 @@ static inline void mt_set_in_rcu(struct maple_tree *mt)
 		return;
 
 	if (mt_external_lock(mt)) {
-		BUG_ON(!mt_lock_is_held(mt));
+		WARN_ON(!mt_lock_is_held(mt));
 		mt->ma_flags |= MT_FLAGS_USE_RCU;
 	} else {
 		mtree_lock(mt);