null_blk: fix ida error handling in null_add_dev()

There needs to be some error checking if ida_simple_get() fails.
Also call ida_free() if there are errors later.

Fixes: 94bc02e3 ("nullb: use ida to manage index")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/YtEhXsr6vJeoiYhd@kiliSigned-off-by: NJens Axboe <axboe@kernel.dk>

drivers/block/null_blk/main.c

@@ -2090,8 +2090,13 @@ static int null_add_dev(struct nullb_device *dev)
 	blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, nullb->q);
 
 	mutex_lock(&lock);
-	nullb->index = ida_simple_get(&nullb_indexes, 0, 0, GFP_KERNEL);
-	dev->index = nullb->index;
+	rv = ida_simple_get(&nullb_indexes, 0, 0, GFP_KERNEL);
+	if (rv < 0) {
+		mutex_unlock(&lock);
+		goto out_cleanup_zone;
+	}
+	nullb->index = rv;
+	dev->index = rv;
 	mutex_unlock(&lock);
 
 	blk_queue_logical_block_size(nullb->q, dev->blocksize);
@@ -2117,7 +2122,7 @@ static int null_add_dev(struct nullb_device *dev)
 
 	rv = null_gendisk_register(nullb);
 	if (rv)
-		goto out_cleanup_zone;
+		goto out_ida_free;
 
 	mutex_lock(&lock);
 	list_add_tail(&nullb->list, &nullb_list);
@@ -2126,6 +2131,9 @@ static int null_add_dev(struct nullb_device *dev)
 	pr_info("disk %s created\n", nullb->disk_name);
 
 	return 0;
+
+out_ida_free:
+	ida_free(&nullb_indexes, nullb->index);
 out_cleanup_zone:
 	null_free_zoned_dev(dev);
 out_cleanup_disk: