drbd: Basic refcounting for drbd_tconn

References hold by:
 * Each (running) drbd thread has a reference on tconn
 * Each mdev has a referenc on tconn
 * Beeing in the all_tconn list counts for one reference
 * Each after_conn_state_chg_work has a reference to tconn

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

drivers/block/drbd/drbd_int.h

@@ -828,6 +828,7 @@ enum {
 struct drbd_tconn {			/* is a resource from the config file */
 	char *name;			/* Resource name */
 	struct list_head all_tconn;	/* linked on global drbd_tconns */
+	struct kref kref;
 	struct idr volumes;		/* <tconn, vnr> to mdev mapping */
 	enum drbd_conns cstate;		/* Only C_STANDALONE to C_WF_REPORT_PARAMS */
 	unsigned susp:1;		/* IO suspended by user */
@@ -1378,8 +1379,8 @@ extern int conn_lowest_minor(struct drbd_tconn *tconn);
 enum drbd_ret_code conn_new_minor(struct drbd_tconn *tconn, unsigned int minor, int vnr);
 extern void drbd_delete_device(struct drbd_conf *mdev);
 
-struct drbd_tconn *drbd_new_tconn(const char *name);
-extern void drbd_free_tconn(struct drbd_tconn *tconn);
+struct drbd_tconn *conn_create(const char *name);
+extern void conn_destroy(struct kref *kref);
 struct drbd_tconn *conn_by_name(const char *name);
 extern void conn_free_crypto(struct drbd_tconn *tconn);
 

drivers/block/drbd/drbd_main.c

@@ -509,6 +509,8 @@ restart:
 	conn_info(tconn, "Terminating %s\n", current->comm);
 
 	/* Release mod reference taken when thread was started */
+
+	kref_put(&tconn->kref, &conn_destroy);
 	module_put(THIS_MODULE);
 	return retval;
 }
@@ -546,6 +548,8 @@ int drbd_thread_start(struct drbd_thread *thi)
 			return false;
 		}
 
+		kref_get(&thi->tconn->kref);
+
 		init_completion(&thi->stop);
 		thi->reset_cpu_mask = 1;
 		thi->t_state = RUNNING;
@@ -558,6 +562,7 @@ int drbd_thread_start(struct drbd_thread *thi)
 		if (IS_ERR(nt)) {
 			conn_err(tconn, "Couldn't start thread\n");
 
+			kref_put(&tconn->kref, &conn_destroy);
 			module_put(THIS_MODULE);
 			return false;
 		}
@@ -2237,6 +2242,8 @@ static void drbd_release_all_peer_reqs(struct drbd_conf *mdev)
 /* caution. no locking. */
 void drbd_delete_device(struct drbd_conf *mdev)
 {
+	struct drbd_tconn *tconn = mdev->tconn;
+
 	idr_remove(&mdev->tconn->volumes, mdev->vnr);
 	idr_remove(&minors, mdev_to_minor(mdev));
 	synchronize_rcu();
@@ -2272,6 +2279,8 @@ void drbd_delete_device(struct drbd_conf *mdev)
 	put_disk(mdev->vdisk);
 	blk_cleanup_queue(mdev->rq_queue);
 	kfree(mdev);
+
+	kref_put(&tconn->kref, &conn_destroy);
 }
 
 static void drbd_cleanup(void)
@@ -2409,7 +2418,7 @@ void conn_free_crypto(struct drbd_tconn *tconn)
 	tconn->int_dig_vv = NULL;
 }
 
-struct drbd_tconn *drbd_new_tconn(const char *name)
+struct drbd_tconn *conn_create(const char *name)
 {
 	struct drbd_tconn *tconn;
 
@@ -2455,6 +2464,7 @@ struct drbd_tconn *drbd_new_tconn(const char *name)
 	};
 
 	down_write(&drbd_cfg_rwsem);
+	kref_init(&tconn->kref);
 	list_add_tail(&tconn->all_tconn, &drbd_tconns);
 	up_write(&drbd_cfg_rwsem);
 
@@ -2471,9 +2481,10 @@ fail:
 	return NULL;
 }
 
-void drbd_free_tconn(struct drbd_tconn *tconn)
+void conn_destroy(struct kref *kref)
 {
-	list_del(&tconn->all_tconn);
+	struct drbd_tconn *tconn = container_of(kref, struct drbd_tconn, kref);
+
 	idr_destroy(&tconn->volumes);
 
 	free_cpumask_var(tconn->cpu_mask);
@@ -2503,7 +2514,9 @@ enum drbd_ret_code conn_new_minor(struct drbd_tconn *tconn, unsigned int minor,
 	if (!mdev)
 		return ERR_NOMEM;
 
+	kref_get(&tconn->kref);
 	mdev->tconn = tconn;
+
 	mdev->minor = minor;
 	mdev->vnr = vnr;
 
@@ -2605,6 +2618,7 @@ out_no_disk:
 	blk_cleanup_queue(q);
 out_no_q:
 	kfree(mdev);
+	kref_put(&tconn->kref, &conn_destroy);
 	return err;
 }
 

drivers/block/drbd/drbd_nl.c

@@ -479,6 +479,7 @@ static int _try_outdate_peer_async(void *data)
 
 	conn_try_outdate_peer(tconn);
 
+	kref_put(&tconn->kref, &conn_destroy);
 	return 0;
 }
 
@@ -486,9 +487,12 @@ void conn_try_outdate_peer_async(struct drbd_tconn *tconn)
 {
 	struct task_struct *opa;
 
+	kref_get(&tconn->kref);
 	opa = kthread_run(_try_outdate_peer_async, tconn, "drbd_async_h");
-	if (IS_ERR(opa))
+	if (IS_ERR(opa)) {
 		conn_err(tconn, "out of mem, failed to invoke fence-peer helper\n");
+		kref_put(&tconn->kref, &conn_destroy);
+	}
 }
 
 enum drbd_state_rv
@@ -2627,7 +2631,7 @@ int get_one_status(struct sk_buff *skb, struct netlink_callback *cb)
 	 * on each iteration.
 	 */
 
-	/* synchronize with drbd_new_tconn/drbd_free_tconn */
+	/* synchronize with conn_create()/conn_destroy() */
 	down_read(&drbd_cfg_rwsem);
 	/* revalidate iterator position */
 	list_for_each_entry(tmp, &drbd_tconns, all_tconn) {
@@ -2932,7 +2936,7 @@ int drbd_adm_create_connection(struct sk_buff *skb, struct genl_info *info)
 		goto out;
 	}
 
-	if (!drbd_new_tconn(adm_ctx.conn_name))
+	if (!conn_create(adm_ctx.conn_name))
 		retcode = ERR_NOMEM;
 out:
 	drbd_adm_finish(info, retcode);
@@ -3005,10 +3009,6 @@ int drbd_adm_delete_minor(struct sk_buff *skb, struct genl_info *info)
 	down_write(&drbd_cfg_rwsem);
 	retcode = adm_delete_minor(adm_ctx.mdev);
 	up_write(&drbd_cfg_rwsem);
-	/* if this was the last volume of this connection,
-	 * this will terminate all threads */
-	if (retcode == NO_ERROR)
-		conn_reconfig_done(adm_ctx.tconn);
 out:
 	drbd_adm_finish(info, retcode);
 	return 0;
@@ -3078,7 +3078,9 @@ int drbd_adm_down(struct sk_buff *skb, struct genl_info *info)
 
 	/* delete connection */
 	if (conn_lowest_minor(adm_ctx.tconn) < 0) {
-		drbd_free_tconn(adm_ctx.tconn);
+		list_del(&adm_ctx.tconn->all_tconn);
+		kref_put(&adm_ctx.tconn->kref, &conn_destroy);
+
 		retcode = NO_ERROR;
 	} else {
 		/* "can not happen" */
@@ -3107,7 +3109,9 @@ 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) {
-		drbd_free_tconn(adm_ctx.tconn);
+		list_del(&adm_ctx.tconn->all_tconn);
+		kref_put(&adm_ctx.tconn->kref, &conn_destroy);
+
 		retcode = NO_ERROR;
 	} else {
 		retcode = ERR_CONN_IN_USE;

drivers/block/drbd/drbd_state.c

@@ -1460,6 +1460,7 @@ static int w_after_conn_state_ch(struct drbd_work *w, int unused)
 
 	//conn_err(tconn, STATE_FMT, STATE_ARGS("nms", nms));
 	after_all_state_ch(tconn);
+	kref_put(&tconn->kref, &conn_destroy);
 
 	return 0;
 }
@@ -1686,6 +1687,7 @@ _conn_request_state(struct drbd_tconn *tconn, union drbd_state mask, union drbd_
 		acscw->ns_max = ns_max;
 		acscw->flags = flags;
 		acscw->w.cb = w_after_conn_state_ch;
+		kref_get(&tconn->kref);
 		acscw->w.tconn = tconn;
 		drbd_queue_work(&tconn->data.work, &acscw->w);
 	} else {