security: Apply lockdep-based checking to rcu_dereference() uses

Apply lockdep-ified RCU primitives to key_gc_keyring() and
keyring_destroy().

Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1266887105-1528-12-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

security/keys/gc.c

@@ -77,7 +77,8 @@ static bool key_gc_keyring(struct key *keyring, time_t limit)
 		goto dont_gc;
 
 	/* scan the keyring looking for dead keys */
-	klist = rcu_dereference(keyring->payload.subscriptions);
+	klist = rcu_dereference_check(keyring->payload.subscriptions,
+				      lockdep_is_held(&key_serial_lock));
 	if (!klist)
 		goto dont_gc;
 

security/keys/keyring.c

@@ -151,7 +151,9 @@ static void keyring_destroy(struct key *keyring)
 		write_unlock(&keyring_name_lock);
 	}
 
-	klist = rcu_dereference(keyring->payload.subscriptions);
+	klist = rcu_dereference_check(keyring->payload.subscriptions,
+				      rcu_read_lock_held() ||
+				      atomic_read(&keyring->usage) == 0);
 	if (klist) {
 		for (loop = klist->nkeys - 1; loop >= 0; loop--)
 			key_put(klist->keys[loop]);