[PATCH 1/5] lockdep: Introduce lockdep_unregister_key_nosync()

[Bart Van Assche <bvanassche@acm.org>]

Add a variant of lockdep_unregister_key() that doesn't sleep and hence
that may be called from inside RCU callbacks.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 include/linux/lockdep.h  |  5 +++++
 kernel/locking/lockdep.c | 22 +++++++++++++++++++---
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 67964dc4db95..afb3f0ec7304 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -117,6 +117,7 @@ do {							\
 } while (0)
 
 extern void lockdep_register_key(struct lock_class_key *key);
+extern void lockdep_unregister_key_nosync(struct lock_class_key *key);
 extern void lockdep_unregister_key(struct lock_class_key *key);
 
 /*
@@ -372,6 +373,10 @@ static inline void lockdep_register_key(struct lock_class_key *key)
 {
 }
 
+static inline void lockdep_unregister_key_nosync(struct lock_class_key *key)
+{
+}
+
 static inline void lockdep_unregister_key(struct lock_class_key *key)
 {
 }
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 4470680f0226..6e0423df9ebe 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -6558,8 +6558,11 @@ void lockdep_reset_lock(struct lockdep_map *lock)
  * Unlike lockdep_register_key(), a search is always done to find a matching
  * key irrespective of debug_locks to avoid potential invalid access to freed
  * memory in lock_class entry.
+ *
+ * Does not call synchronize_rcu(). The caller is responsible for making sure
+ * that memory is only freed after concurrent accesses have finished.
  */
-void lockdep_unregister_key(struct lock_class_key *key)
+void lockdep_unregister_key_nosync(struct lock_class_key *key)
 {
 	struct hlist_head *hash_head = keyhashentry(key);
 	struct lock_class_key *k;
@@ -6568,8 +6571,6 @@ void lockdep_unregister_key(struct lock_class_key *key)
 	bool found = false;
 	bool need_callback = false;
 
-	might_sleep();
-
 	if (WARN_ON_ONCE(static_obj(key)))
 		return;
 
@@ -6594,6 +6595,21 @@ void lockdep_unregister_key(struct lock_class_key *key)
 
 	if (need_callback)
 		call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
+}
+EXPORT_SYMBOL_GPL(lockdep_unregister_key_nosync);
+
+/*
+ * Unregister a dynamically allocated key.
+ *
+ * Unlike lockdep_register_key(), a search is always done to find a matching
+ * key irrespective of debug_locks to avoid potential invalid access to freed
+ * memory in lock_class entry.
+ */
+void lockdep_unregister_key(struct lock_class_key *key)
+{
+	might_sleep();
+
+	lockdep_unregister_key_nosync(key);
 
 	/* Wait until is_dynamic_key() has finished accessing k->hash_entry. */
 	synchronize_rcu();