dm snapshot persistent: fix missing cleanup in persistent_ctr error path

If an unsupported option is given then the early return from
persistent_ctr() leaked memory allocated for the 'pstore' and never
destroyed the 'metadata_wq'.

Fixes: b0d3cc011e53 ("dm snapshot: add new persistent store option to support overflow")
Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-snap-persistent.c

@@ -847,6 +847,7 @@ static void persistent_drop_snapshot(struct dm_exception_store *store)
 static int persistent_ctr(struct dm_exception_store *store, char *options)
 {
 	struct pstore *ps;
+	int r;
 
 	/* allocate the pstore */
 	ps = kzalloc(sizeof(*ps), GFP_KERNEL);
@@ -868,9 +869,9 @@ static int persistent_ctr(struct dm_exception_store *store, char *options)
 
 	ps->metadata_wq = alloc_workqueue("ksnaphd", WQ_MEM_RECLAIM, 0);
 	if (!ps->metadata_wq) {
-		kfree(ps);
 		DMERR("couldn't start header metadata update thread");
-		return -ENOMEM;
+		r = -ENOMEM;
+		goto err_workqueue;
 	}
 
 	if (options) {
@@ -879,13 +880,21 @@ static int persistent_ctr(struct dm_exception_store *store, char *options)
 			store->userspace_supports_overflow = true;
 		else {
 			DMERR("Unsupported persistent store option: %s", options);
-			return -EINVAL;
+			r = -EINVAL;
+			goto err_options;
 		}
 	}
 
 	store->context = ps;
 
 	return 0;
+
+err_options:
+	destroy_workqueue(ps->metadata_wq);
+err_workqueue:
+	kfree(ps);
+
+	return r;
 }
 
 static unsigned persistent_status(struct dm_exception_store *store,