[PATCH v2 4/4] maple_tree: Be more strict about locking

[Liam R. Howlett]

Use lockdep to check the write path in the maple tree holds the lock in
write mode.

Introduce mt_write_lock_is_held() to check if the lock is held for
writing.  Update the necessary checks for rcu_dereference_protected() to
use the new write lock check.

Cc: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Liam R. Howlett <Liam.Howlett at oracle.com>
---
 include/linux/maple_tree.h |  7 ++++++-
 lib/maple_tree.c           | 10 ++++++++--
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
index 6618c1512886..43f18230cfa4 100644
--- a/include/linux/maple_tree.h
+++ b/include/linux/maple_tree.h
@@ -185,11 +185,16 @@ typedef struct lockdep_map *lockdep_map_p;
 #define mt_lock_is_held(mt)                                             \
 	(!(mt)->ma_external_lock || lock_is_held((mt)->ma_external_lock))
 
+#define mt_write_lock_is_held(mt)					\
+	(!(mt)->ma_external_lock ||					\
+	 lock_is_held_type((mt)->ma_external_lock, 0))
+
 #define mt_set_external_lock(mt, lock)					\
 	(mt)->ma_external_lock = &(lock)->dep_map
 #else
 typedef struct { /* nothing */ } lockdep_map_p;
-#define mt_lock_is_held(mt)	1
+#define mt_lock_is_held(mt)		1
+#define mt_write_lock_is_held(mt)	1
 #define mt_set_external_lock(mt, lock)	do { } while (0)
 #endif
 
diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index cef47ce8eddd..722c78077b25 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -777,6 +777,12 @@ static inline void __rcu **ma_slots(struct maple_node *mn, enum maple_type mt)
 	}
 }
 
+static inline bool mt_write_locked(const struct maple_tree *mt)
+{
+	return mt_external_lock(mt) ? mt_write_lock_is_held(mt) :
+		lockdep_is_held(&mt->ma_lock);
+}
+
 static inline bool mt_locked(const struct maple_tree *mt)
 {
 	return mt_external_lock(mt) ? mt_lock_is_held(mt) :
@@ -792,7 +798,7 @@ static inline void *mt_slot(const struct maple_tree *mt,
 static inline void *mt_slot_locked(struct maple_tree *mt, void __rcu **slots,
 				   unsigned char offset)
 {
-	return rcu_dereference_protected(slots[offset], mt_locked(mt));
+	return rcu_dereference_protected(slots[offset], mt_write_locked(mt));
 }
 /*
  * mas_slot_locked() - Get the slot value when holding the maple tree lock.
@@ -835,7 +841,7 @@ static inline void *mas_root(struct ma_state *mas)
 
 static inline void *mt_root_locked(struct maple_tree *mt)
 {
-	return rcu_dereference_protected(mt->ma_root, mt_locked(mt));
+	return rcu_dereference_protected(mt->ma_root, mt_write_locked(mt));
 }
 
 /*
-- 
2.39.2