net: Use rtnl_net_dev_lock() in register_netdevice_notifier_dev_net().

Breno Leitao reported the splat below. [0]

Commit 65161fb ("net: Fix dev_net(dev) race in
unregister_netdevice_notifier_dev_net().") added the
DEBUG_NET_WARN_ON_ONCE(), assuming that the netdev is not
registered before register_netdevice_notifier_dev_net().

But the assumption was simply wrong.

Let's use rtnl_net_dev_lock() in register_netdevice_notifier_dev_net().

[0]:
WARNING: CPU: 25 PID: 849 at net/core/dev.c:2150 register_netdevice_notifier_dev_net (net/core/dev.c:2150)
 <TASK>
 ? __warn (kernel/panic.c:242 kernel/panic.c:748)
 ? register_netdevice_notifier_dev_net (net/core/dev.c:2150)
 ? register_netdevice_notifier_dev_net (net/core/dev.c:2150)
 ? report_bug (lib/bug.c:? lib/bug.c:219)
 ? handle_bug (arch/x86/kernel/traps.c:285)
 ? exc_invalid_op (arch/x86/kernel/traps.c:309)
 ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:621)
 ? register_netdevice_notifier_dev_net (net/core/dev.c:2150)
 ? register_netdevice_notifier_dev_net (./include/net/net_namespace.h:406 ./include/linux/netdevice.h:2663 net/core/dev.c:2144)
 mlx5e_mdev_notifier_event+0x9f/0xf0 mlx5_ib
 notifier_call_chain.llvm.12241336988804114627 (kernel/notifier.c:85)
 blocking_notifier_call_chain (kernel/notifier.c:380)
 mlx5_core_uplink_netdev_event_replay (drivers/net/ethernet/mellanox/mlx5/core/main.c:352)
 mlx5_ib_roce_init.llvm.12447516292400117075+0x1c6/0x550 mlx5_ib
 mlx5r_probe+0x375/0x6a0 mlx5_ib
 ? kernfs_put (./include/linux/instrumented.h:96 ./include/linux/atomic/atomic-arch-fallback.h:2278 ./include/linux/atomic/atomic-instrumented.h:1384 fs/kernfs/dir.c:557)
 ? auxiliary_match_id (drivers/base/auxiliary.c:174)
 ? mlx5r_mp_remove+0x160/0x160 mlx5_ib
 really_probe (drivers/base/dd.c:? drivers/base/dd.c:658)
 driver_probe_device (drivers/base/dd.c:830)
 __driver_attach (drivers/base/dd.c:1217)
 bus_for_each_dev (drivers/base/bus.c:369)
 ? driver_attach (drivers/base/dd.c:1157)
 bus_add_driver (drivers/base/bus.c:679)
 driver_register (drivers/base/driver.c:249)

Fixes: 7fb1073 ("net: Hold rtnl_net_lock() in (un)?register_netdevice_notifier_dev_net().")
Reported-by: Breno Leitao <leitao@debian.org>
Closes: https://lore.kernel.org/netdev/20250224-noisy-cordial-roadrunner-fad40c@leitao/
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Tested-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20250225211023.96448-1-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: q2ven

net/core/dev.c

@@ -2141,21 +2141,15 @@ int register_netdevice_notifier_dev_net(struct net_device *dev,
 					struct notifier_block *nb,
 					struct netdev_net_notifier *nn)
 {
-	struct net *net = dev_net(dev);
 	int err;
 
-	/* rtnl_net_lock() assumes dev is not yet published by
-	 * register_netdevice().
-	 */
-	DEBUG_NET_WARN_ON_ONCE(!list_empty(&dev->dev_list));
-
-	rtnl_net_lock(net);
-	err = __register_netdevice_notifier_net(net, nb, false);
+	rtnl_net_dev_lock(dev);
+	err = __register_netdevice_notifier_net(dev_net(dev), nb, false);
 	if (!err) {
 		nn->nb = nb;
 		list_add(&nn->list, &dev->net_notifier_list);
 	}
-	rtnl_net_unlock(net);
+	rtnl_net_dev_unlock(dev);
 
 	return err;
 }