drbd: Use RCU for the drbd_tconns list

Preparing removal of drbd_cfg_rwsem

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_main.c

@@ -2341,7 +2341,7 @@ static void drbd_cleanup(void)
 	}
 
 	list_for_each_entry_safe(tconn, tmp, &drbd_tconns, all_tconn) {
-		list_del(&tconn->all_tconn);
+		list_del_rcu(&tconn->all_tconn);
 		synchronize_rcu();
 		kref_put(&tconn->kref, &conn_destroy);
 	}
@@ -2409,7 +2409,7 @@ struct drbd_tconn *conn_get_by_name(const char *name)
 		return NULL;
 
 	down_read(&drbd_cfg_rwsem);
-	list_for_each_entry(tconn, &drbd_tconns, all_tconn) {
+	list_for_each_entry_rcu(tconn, &drbd_tconns, all_tconn) {
 		if (!strcmp(tconn->name, name)) {
 			kref_get(&tconn->kref);
 			goto found;
@@ -2459,6 +2459,7 @@ void conn_free_crypto(struct drbd_tconn *tconn)
 	tconn->int_dig_vv = NULL;
 }
 
+/* caller must be under genl_lock() */
 struct drbd_tconn *conn_create(const char *name)
 {
 	struct drbd_tconn *tconn;
@@ -2503,7 +2504,7 @@ struct drbd_tconn *conn_create(const char *name)
 
 	down_write(&drbd_cfg_rwsem);
 	kref_init(&tconn->kref);
-	list_add_tail(&tconn->all_tconn, &drbd_tconns);
+	list_add_tail_rcu(&tconn->all_tconn, &drbd_tconns);
 	up_write(&drbd_cfg_rwsem);
 
 	return tconn;

drivers/block/drbd/drbd_nl.c

@@ -2674,7 +2674,7 @@ int get_one_status(struct sk_buff *skb, struct netlink_callback *cb)
 	/* synchronize with conn_create()/conn_destroy() */
 	down_read(&drbd_cfg_rwsem);
 	/* revalidate iterator position */
-	list_for_each_entry(tmp, &drbd_tconns, all_tconn) {
+	list_for_each_entry_rcu(tmp, &drbd_tconns, all_tconn) {
 		if (pos == NULL) {
 			/* first iteration */
 			pos = tmp;
@@ -2692,8 +2692,8 @@ next_tconn:
 		if (!mdev) {
 			/* No more volumes to dump on this tconn.
 			 * Advance tconn iterator. */
-			pos = list_entry(tconn->all_tconn.next,
-					struct drbd_tconn, all_tconn);
+			pos = list_entry_rcu(tconn->all_tconn.next,
+					     struct drbd_tconn, all_tconn);
 			/* Did we dump any volume on this tconn yet? */
 			if (volume != 0) {
 				/* If we reached the end of the list,
@@ -3130,7 +3130,8 @@ int drbd_adm_down(struct sk_buff *skb, struct genl_info *info)
 
 	/* delete connection */
 	if (conn_lowest_minor(adm_ctx.tconn) < 0) {
-		list_del(&adm_ctx.tconn->all_tconn);
+		list_del_rcu(&adm_ctx.tconn->all_tconn);
+		synchronize_rcu();
 		kref_put(&adm_ctx.tconn->kref, &conn_destroy);
 
 		retcode = NO_ERROR;
@@ -3160,7 +3161,8 @@ int drbd_adm_delete_connection(struct sk_buff *skb, struct genl_info *info)
 
 	down_write(&drbd_cfg_rwsem);
 	if (conn_lowest_minor(adm_ctx.tconn) < 0) {
-		list_del(&adm_ctx.tconn->all_tconn);
+		list_del_rcu(&adm_ctx.tconn->all_tconn);
+		synchronize_rcu();
 		kref_put(&adm_ctx.tconn->kref, &conn_destroy);
 
 		retcode = NO_ERROR;