[PATCH] maple_tree: Stop flooding logs when debug_locks is set to zero

[Liam R. Howlett (Oracle)]

When lockdep detects an issue, it sets debug_locks to 0 disabling
further reports.  The newly added maple tree sequence counting on locks
to detect errors is not taking this nor the fact that lock_is_held() can
return -1 (unknown state) into account.  The resulting action is a flood
of logging of not matching sequence numbers being reported on failure.

__lock_sequnece() will return u32 ~0 when debug_locks is zero, and the
real sequnece count cannot return such a high value as it is less than
32bits.

By always updating the sequence number, regardless of lock state and by
ignoring ~0 value in the sequence number will avoid ever printing a
WARN_ON when this condition is hit.

Signed-off-by: Liam R. Howlett (Oracle) <liam@xxxxxxxxxxxxx>
---
 lib/maple_tree.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 06cc05b79fbdc..2280be62235ca 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -1173,6 +1173,8 @@ static void mas_lock_check(struct ma_state *mas)
 {
 #ifdef CONFIG_LOCKDEP
 	struct lockdep_map *map;
+	u32 seq;
+
 	if (!mas_is_active(mas))
 		return;
 
@@ -1184,8 +1186,12 @@ static void mas_lock_check(struct ma_state *mas)
 #endif /* CONFIG_RCU_STRICT_GRACE_PERIOD */
 
 	map = mas_lockdep_map(mas);
-	if (map && lock_is_held(map))
-		WARN_ON_ONCE(mas->ld_seq != lock_sequence(map));
+	if (!map)
+		return;
+
+	seq = lock_sequence(map);
+	if (seq != UINT_MAX && mas->ld_seq != UINT_MAX)
+		WARN_ON_ONCE(mas->ld_seq != seq);
 #endif /* CONFIG_LOCKDEP */
 
 }
@@ -1203,8 +1209,8 @@ static void mas_init_lock_check(struct ma_state *mas)
 #endif /* CONFIG_RCU_STRICT_GRACE_PERIOD */
 
 	map = mas_lockdep_map(mas);
-	if (map && lock_is_held(map))
-		mas->ld_seq = lock_sequence(mas_lockdep_map(mas));
+	if (map) /* Update regardless of lock state */
+		mas->ld_seq = lock_sequence(map);
 #endif /* CONFIG_LOCKDEP */
 
 }
-- 
2.47.3


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