nbd: fold nbd config initialization into nbd_alloc_config()

There are no functional changes, make the code cleaner and prepare to
fix null-ptr-dereference while accessing 'nbd->config'.
Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20231116162316.1740402-2-linan666@huaweicloud.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/nbd.c

@@ -1530,17 +1530,20 @@ static int nbd_ioctl(struct block_device *bdev, blk_mode_t mode,
 	return error;
 }
 
-static struct nbd_config *nbd_alloc_config(void)
+static int nbd_alloc_and_init_config(struct nbd_device *nbd)
 {
 	struct nbd_config *config;
 
+	if (WARN_ON(nbd->config))
+		return -EINVAL;
+
 	if (!try_module_get(THIS_MODULE))
-		return ERR_PTR(-ENODEV);
+		return -ENODEV;
 
 	config = kzalloc(sizeof(struct nbd_config), GFP_NOFS);
 	if (!config) {
 		module_put(THIS_MODULE);
-		return ERR_PTR(-ENOMEM);
+		return -ENOMEM;
 	}
 
 	atomic_set(&config->recv_threads, 0);
@@ -1548,7 +1551,10 @@ static struct nbd_config *nbd_alloc_config(void)
 	init_waitqueue_head(&config->conn_wait);
 	config->blksize_bits = NBD_DEF_BLKSIZE_BITS;
 	atomic_set(&config->live_connections, 0);
-	return config;
+	nbd->config = config;
+	refcount_set(&nbd->config_refs, 1);
+
+	return 0;
 }
 
 static int nbd_open(struct gendisk *disk, blk_mode_t mode)
@@ -1567,21 +1573,17 @@ static int nbd_open(struct gendisk *disk, blk_mode_t mode)
 		goto out;
 	}
 	if (!refcount_inc_not_zero(&nbd->config_refs)) {
-		struct nbd_config *config;
-
 		mutex_lock(&nbd->config_lock);
 		if (refcount_inc_not_zero(&nbd->config_refs)) {
 			mutex_unlock(&nbd->config_lock);
 			goto out;
 		}
-		config = nbd_alloc_config();
-		if (IS_ERR(config)) {
-			ret = PTR_ERR(config);
+		ret = nbd_alloc_and_init_config(nbd);
+		if (ret) {
 			mutex_unlock(&nbd->config_lock);
 			goto out;
 		}
-		nbd->config = config;
-		refcount_set(&nbd->config_refs, 1);
+
 		refcount_inc(&nbd->refs);
 		mutex_unlock(&nbd->config_lock);
 		if (max_part)
@@ -1990,22 +1992,17 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
 		pr_err("nbd%d already in use\n", index);
 		return -EBUSY;
 	}
-	if (WARN_ON(nbd->config)) {
-		mutex_unlock(&nbd->config_lock);
-		nbd_put(nbd);
-		return -EINVAL;
-	}
-	config = nbd_alloc_config();
-	if (IS_ERR(config)) {
+
+	ret = nbd_alloc_and_init_config(nbd);
+	if (ret) {
 		mutex_unlock(&nbd->config_lock);
 		nbd_put(nbd);
 		pr_err("couldn't allocate config\n");
-		return PTR_ERR(config);
+		return ret;
 	}
-	nbd->config = config;
-	refcount_set(&nbd->config_refs, 1);
-	set_bit(NBD_RT_BOUND, &config->runtime_flags);
 
+	config = nbd->config;
+	set_bit(NBD_RT_BOUND, &config->runtime_flags);
 	ret = nbd_genl_size_set(info, nbd);
 	if (ret)
 		goto out;