Re: [PATCH] nvme-tcp: Use __dev_get_by_name instead dev_get_by_name for OPT_HOST_IFACE

[Christoph Hellwig <hch@lst.de>]

I've applied the slightly updated version below to make it a little
more clear what is going on:

---
From 9de7d173c10b6be09fe9d5b7010ef182465897a1 Mon Sep 17 00:00:00 2001
From: Prabhakar Kushwaha <pkushwaha@marvell.com>
Date: Fri, 18 Jun 2021 16:39:56 +0300
Subject: nvme-tcp: use __dev_get_by_name instead dev_get_by_name for
 OPT_HOST_IFACE

dev_get_by_name() finds network device by name but it also increases the
reference count.

If a nvme-tcp queue is present and the network device driver is removed
before nvme_tcp, we will face the following continuous log:

  "kernel:unregister_netdevice: waiting for <eth> to become free. Usage count = 2"

And rmmod further halts. Similar case arises during reboot/shutdown
with nvme-tcp queue present and both never completes.

To fix this, use __dev_get_by_name() which finds network device by
name without increasing any reference counter.

Fixes: 3ede8f72a9a2 ("nvme-tcp: allow selecting the network interface for connections")
Signed-off-by: Omkar Kulkarni <okulkarni@marvell.com>
Signed-off-by: Shai Malin <smalin@marvell.com>
Signed-off-by: Prabhakar Kushwaha <pkushwaha@marvell.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
[hch: remove the ->ndev member entirely]
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/nvme/host/tcp.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index c7bd37103cf4..2b46c6e0226f 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -123,7 +123,6 @@ struct nvme_tcp_ctrl {
 	struct blk_mq_tag_set	admin_tag_set;
 	struct sockaddr_storage addr;
 	struct sockaddr_storage src_addr;
-	struct net_device	*ndev;
 	struct nvme_ctrl	ctrl;
 
 	struct work_struct	err_work;
@@ -2533,8 +2532,7 @@ static struct nvme_ctrl *nvme_tcp_create_ctrl(struct device *dev,
 	}
 
 	if (opts->mask & NVMF_OPT_HOST_IFACE) {
-		ctrl->ndev = dev_get_by_name(&init_net, opts->host_iface);
-		if (!ctrl->ndev) {
+		if (!__dev_get_by_name(&init_net, opts->host_iface)) {
 			pr_err("invalid interface passed: %s\n",
 			       opts->host_iface);
 			ret = -ENODEV;
-- 
2.30.2


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