drbd: Take a reference on tconn when finding a tconn by name

Rule #3 of kref.txt

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

Author: Philipp-Reisner

drivers/block/drbd/drbd_int.h

@@ -1381,7 +1381,7 @@ extern void drbd_delete_device(struct drbd_conf *mdev);
 
 struct drbd_tconn *conn_create(const char *name);
 extern void conn_destroy(struct kref *kref);
-struct drbd_tconn *conn_by_name(const char *name);
+struct drbd_tconn *conn_get_by_name(const char *name);
 extern void conn_free_crypto(struct drbd_tconn *tconn);
 
 extern int proc_details;

drivers/block/drbd/drbd_main.c

@@ -2362,7 +2362,7 @@ static void drbd_init_workqueue(struct drbd_work_queue* wq)
 	INIT_LIST_HEAD(&wq->q);
 }
 
-struct drbd_tconn *conn_by_name(const char *name)
+struct drbd_tconn *conn_get_by_name(const char *name)
 {
 	struct drbd_tconn *tconn;
 
@@ -2371,8 +2371,10 @@ struct drbd_tconn *conn_by_name(const char *name)
 
 	down_read(&drbd_cfg_rwsem);
 	list_for_each_entry(tconn, &drbd_tconns, all_tconn) {
-		if (!strcmp(tconn->name, name))
+		if (!strcmp(tconn->name, name)) {
+			kref_get(&tconn->kref);
 			goto found;
+		}
 	}
 	tconn = NULL;
 found:

drivers/block/drbd/drbd_nl.c

@@ -195,7 +195,7 @@ static int drbd_adm_prepare(struct sk_buff *skb, struct genl_info *info,
 
 	adm_ctx.minor = d_in->minor;
 	adm_ctx.mdev = minor_to_mdev(d_in->minor);
-	adm_ctx.tconn = conn_by_name(adm_ctx.conn_name);
+	adm_ctx.tconn = conn_get_by_name(adm_ctx.conn_name);
 
 	if (!adm_ctx.mdev && (flags & DRBD_ADM_NEED_MINOR)) {
 		drbd_msg_put_info("unknown minor");
@@ -223,8 +223,7 @@ static int drbd_adm_prepare(struct sk_buff *skb, struct genl_info *info,
 		drbd_msg_put_info("minor exists as different volume");
 		return ERR_INVALID_REQUEST;
 	}
-	if (adm_ctx.mdev && !adm_ctx.tconn)
-		adm_ctx.tconn = adm_ctx.mdev->tconn;
+
 	return NO_ERROR;
 
 fail:
@@ -238,6 +237,11 @@ static int drbd_adm_finish(struct genl_info *info, int retcode)
 	struct nlattr *nla;
 	const char *conn_name = NULL;
 
+	if (adm_ctx.tconn) {
+		kref_put(&adm_ctx.tconn->kref, &conn_destroy);
+		adm_ctx.tconn = NULL;
+	}
+
 	if (!adm_ctx.reply_skb)
 		return -ENOMEM;
 
@@ -2748,10 +2752,13 @@ int drbd_adm_get_status_all(struct sk_buff *skb, struct netlink_callback *cb)
 	if (!nla)
 		return -EINVAL;
 	conn_name = nla_data(nla);
-	tconn = conn_by_name(conn_name);
+	tconn = conn_get_by_name(conn_name);
+
 	if (!tconn)
 		return -ENODEV;
 
+	kref_put(&tconn->kref, &conn_destroy); /* get_one_status() (re)validates tconn by itself */
+
 	/* prime iterators, and set "filter" mode mark:
 	 * only dump this tconn. */
 	cb->args[0] = (long)tconn;