linux-kernel - [PATCH -next 2/3] nbd: factor out a helper to get nbd_config without holding 'config

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Date:   Fri,  7 Jul 2023 11:15:35 +0800
From:   Zhong Jinghua <zhongjinghua@...weicloud.com>
To:     josef@...icpanda.com, axboe@...nel.dk
Cc:     linux-block@...r.kernel.org, nbd@...er.debian.org,
        linux-kernel@...r.kernel.org, zhongjinghua@...weicloud.com,
        yi.zhang@...wei.com, yukuai3@...wei.com
Subject: [PATCH -next 2/3] nbd: factor out a helper to get nbd_config without holding 'config_lock'

From: Zhong Jinghua <zhongjinghua@...wei.com>

There are no functional changes, just to make code cleaner and prepare
to fix null-ptr-dereference while accessing 'nbd->config'.

Signed-off-by: Zhong Jinghua <zhongjinghua@...wei.com>
---
 drivers/block/nbd.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index cd6d78914954..7186a9a49445 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -393,6 +393,14 @@ static u32 req_to_nbd_cmd_type(struct request *req)
 	}
 }
 
+static struct nbd_config *nbd_get_config_unlocked(struct nbd_device *nbd)
+{
+	if (refcount_inc_not_zero(&nbd->config_refs))
+		return nbd->config;
+
+	return NULL;
+}
+
 static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req)
 {
 	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
@@ -407,13 +415,13 @@ static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req)
 		return BLK_EH_DONE;
 	}
 
-	if (!refcount_inc_not_zero(&nbd->config_refs)) {
+	config = nbd_get_config_unlocked(nbd);
+	if (!config) {
 		cmd->status = BLK_STS_TIMEOUT;
 		__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
 		mutex_unlock(&cmd->lock);
 		goto done;
 	}
-	config = nbd->config;
 
 	if (config->num_connections > 1 ||
 	    (config->num_connections == 1 && nbd->tag_set.timeout)) {
@@ -975,12 +983,12 @@ static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)
 	struct nbd_sock *nsock;
 	int ret;
 
-	if (!refcount_inc_not_zero(&nbd->config_refs)) {
+	config = nbd_get_config_unlocked(nbd);
+	if (!config) {
 		dev_err_ratelimited(disk_to_dev(nbd->disk),
 				    "Socks array is empty\n");
 		return -EINVAL;
 	}
-	config = nbd->config;
 
 	if (index >= config->num_connections) {
 		dev_err_ratelimited(disk_to_dev(nbd->disk),
@@ -1556,6 +1564,7 @@ static int nbd_alloc_and_init_config(struct nbd_device *nbd)
 static int nbd_open(struct block_device *bdev, fmode_t mode)
 {
 	struct nbd_device *nbd;
+	struct nbd_config *config;
 	int ret = 0;
 
 	mutex_lock(&nbd_index_mutex);
@@ -1568,7 +1577,9 @@ static int nbd_open(struct block_device *bdev, fmode_t mode)
 		ret = -ENXIO;
 		goto out;
 	}
-	if (!refcount_inc_not_zero(&nbd->config_refs)) {
+
+	config = nbd_get_config_unlocked(nbd);
+	if (!config) {
 		mutex_lock(&nbd->config_lock);
 		if (refcount_inc_not_zero(&nbd->config_refs)) {
 			mutex_unlock(&nbd->config_lock);
@@ -1584,7 +1595,7 @@ static int nbd_open(struct block_device *bdev, fmode_t mode)
 		mutex_unlock(&nbd->config_lock);
 		if (max_part)
 			set_bit(GD_NEED_PART_SCAN, &bdev->bd_disk->state);
-	} else if (nbd_disconnected(nbd->config)) {
+	} else if (nbd_disconnected(config)) {
 		if (max_part)
 			set_bit(GD_NEED_PART_SCAN, &bdev->bd_disk->state);
 	}
@@ -2194,7 +2205,8 @@ static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
 	}
 	mutex_unlock(&nbd_index_mutex);
 
-	if (!refcount_inc_not_zero(&nbd->config_refs)) {
+	config = nbd_get_config_unlocked(nbd);
+	if (!config) {
 		dev_err(nbd_to_dev(nbd),
 			"not configured, cannot reconfigure\n");
 		nbd_put(nbd);
@@ -2202,7 +2214,6 @@ static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
 	}
 
 	mutex_lock(&nbd->config_lock);
-	config = nbd->config;
 	if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
 	    !nbd->pid) {
 		dev_err(nbd_to_dev(nbd),
-- 
2.31.1