diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index ddd2ed7..8d32f9d 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -40,6 +40,7 @@
 #include <linux/major.h>
 #include <linux/blkdev.h>
 #include <linux/genhd.h>
+#include <linux/idr.h>
 #include <net/tcp.h>
 #include <linux/lru_cache.h>
 #include <linux/prefetch.h>
@@ -916,8 +917,9 @@
 	char *name;			/* Resource name */
 	struct list_head all_tconn;	/* List of all drbd_tconn, prot by global_state_lock */
 	struct drbd_conf *volume0;	/* TODO: Remove me again */
-	unsigned long flags;
+	struct idr volumes;             /* <tconn, vnr> to mdev mapping */
 
+	unsigned long flags;
 	struct net_conf *net_conf;	/* protected by get_net_conf() and put_net_conf() */
 	atomic_t net_cnt;		/* Users of net_conf */
 	wait_queue_head_t net_cnt_wait;
diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 01749e97..254e5c1 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -2183,6 +2183,7 @@
 
 	atomic_set(&tconn->net_cnt, 0);
 	init_waitqueue_head(&tconn->net_cnt_wait);
+	idr_init(&tconn->volumes);
 
 	write_lock_irq(&global_state_lock);
 	list_add(&tconn->all_tconn, &drbd_tconns);
@@ -2202,6 +2203,7 @@
 	write_lock_irq(&global_state_lock);
 	list_del(&tconn->all_tconn);
 	write_unlock_irq(&global_state_lock);
+	idr_destroy(&tconn->volumes);
 
 	kfree(tconn->name);
 	kfree(tconn->int_dig_out);
@@ -2216,6 +2218,7 @@
 	struct gendisk *disk;
 	struct request_queue *q;
 	char conn_name[9]; /* drbd1234N */
+	int vnr;
 
 	/* GFP_KERNEL, we are outside of all write-out paths */
 	mdev = kzalloc(sizeof(struct drbd_conf), GFP_KERNEL);
@@ -2225,7 +2228,14 @@
 	mdev->tconn = drbd_new_tconn(conn_name);
 	if (!mdev->tconn)
 		goto out_no_tconn;
-
+	if (!idr_pre_get(&mdev->tconn->volumes, GFP_KERNEL))
+		goto out_no_cpumask;
+	if (idr_get_new(&mdev->tconn->volumes, mdev, &vnr))
+		goto out_no_cpumask;
+	if (vnr != 0) {
+		dev_err(DEV, "vnr = %d\n", vnr);
+		goto out_no_cpumask;
+	}
 	if (!zalloc_cpumask_var(&mdev->cpu_mask, GFP_KERNEL))
 		goto out_no_cpumask;