[tip:locking/core] locking/lockdep: Make concurrent lockdep_reset_lock() calls safe

[tip-bot for Bart Van Assche]

Commit-ID:  786fa29e9cb6810e21ab0d9c41a81d81d54d1d1b
Gitweb:     https://git.kernel.org/tip/786fa29e9cb6810e21ab0d9c41a81d81d54d1d1b
Author:     Bart Van Assche <bvanassche@xxxxxxx>
AuthorDate: Thu, 6 Dec 2018 17:11:36 -0800
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 11 Dec 2018 14:54:55 +0100

locking/lockdep: Make concurrent lockdep_reset_lock() calls safe

Since zap_class() removes items from the all_lock_classes list and the
classhash_table, protect all zap_class() calls against concurrent
data structure modifications with the graph lock.

Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: johannes.berg@xxxxxxxxx
Cc: tj@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20181207011148.251812-13-bvanassche@xxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/locking/lockdep.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 346b5a1fd062..737d2dd3ea56 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -4122,6 +4122,9 @@ void lockdep_reset(void)
 	raw_local_irq_restore(flags);
 }
 
+/*
+ * Remove all references to a lock class. The caller must hold the graph lock.
+ */
 static void zap_class(struct lock_class *class)
 {
 	int i;
@@ -4229,6 +4232,7 @@ void lockdep_reset_lock(struct lockdep_map *lock)
 	int j, locked;
 
 	raw_local_irq_save(flags);
+	locked = graph_lock();
 
 	/*
 	 * Remove all classes this lock might have:
@@ -4245,7 +4249,6 @@ void lockdep_reset_lock(struct lockdep_map *lock)
 	 * Debug check: in the end all mapped classes should
 	 * be gone.
 	 */
-	locked = graph_lock();
 	if (unlikely(lock_class_cache_is_registered(lock))) {
 		if (debug_locks_off_graph_unlock()) {
 			/*