linux-kernel - [PATCH v3 12/24] locking/lockdep: Make concurrent lockdep_reset

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Date:   Thu,  6 Dec 2018 17:11:36 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     mingo@...hat.com
Cc:     peterz@...radead.org, tj@...nel.org, longman@...hat.com,
        johannes.berg@...el.com, linux-kernel@...r.kernel.org,
        Bart Van Assche <bvanassche@....org>,
        Johannes Berg <johannes@...solutions.net>
Subject: [PATCH v3 12/24] 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.

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Waiman Long <longman@...hat.com>
Cc: Johannes Berg <johannes@...solutions.net>
Signed-off-by: Bart Van Assche <bvanassche@....org>
---
 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()) {
 			/*
-- 
2.20.0.rc2.403.gdbc3b29805-goog