Re: [PATCH net] net: Defer netdev KOBJ_ADD uevent until the device is published

[Jakub Kicinski]

On Tue, 4 Aug 2026 18:51:01 +0300 Dragos Tatulea wrote:
> netdev_register_kobject() calls device_add(), which emits KOBJ_ADD and
> wakes udev, but register_netdevice() only makes the device findable by
> name later, in list_netdevice().  A udev worker that reacts to the uevent
> can therefore run against a device that no lookup can find yet.
> 
> This used to be harmless because the ethtool ioctl took the rtnl_lock
> when looking the device up, and register_netdevice() runs under rtnl, so
> the worker simply blocked until registration finished. The commit in the
> fixes tag moved the lookup out from under rtnl for ops-locked drivers.
> Now there is a short window in register_netdevice() between
> netdev_register_kobject() until list_netdevice() when the device is not
> findable by name.
> 
> This was reproduced with the mlx5 driver on a kernel with KASAN enabled
> during devlink reload: systemd-udevd's net_driver builtin gets -ENODEV
> from ETHTOOL_GDRVINFO, which was preventing interface renaming.
> 
> Suppress the uevent in netdev_register_kobject() and emit it from
> register_netdevice() next to rtmsg_ifinfo(). This is the last point in
> register_netdevice() where no error can happen, so only fully registered
> devices are announced: the registration error paths never reach it, and
> the device_del() that unwinds them stays silent as well, leaving
> userspace with neither an add nor a remove.
> 
> Fixes: f994752b1127 ("net: ethtool: optionally skip rtnl_lock on IOCTL path")
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Dragos Tatulea <dtatulea@xxxxxxxxxx>
> Reviewed-by: Shahar Shitrit <shshitrit@xxxxxxxxxx>

LGTM, one nit..

>  net/core/dev.c       |  1 +
>  net/core/net-sysfs.c | 16 ++++++++++++++++
>  net/core/net-sysfs.h |  1 +
>  3 files changed, 18 insertions(+)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index c1c1be1a6962..32cc092d5d11 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -11499,6 +11499,7 @@ int register_netdevice(struct net_device *dev)
>  	 *	Prevent userspace races by waiting until the network
>  	 *	device is fully setup before sending notifications.
>  	 */
> +	netdev_uevent_add(dev);
>  	if (!(dev->rtnl_link_ops && dev->rtnl_link_initializing))
>  		rtmsg_ifinfo(RTM_NEWLINK, dev, ~0U, GFP_KERNEL, 0, NULL);
>  
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index 0e71c9ed41e8..9a403259a3d0 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -2334,6 +2334,11 @@ int netdev_register_kobject(struct net_device *ndev)
>  		*groups++ = &wireless_group;
>  #endif /* CONFIG_SYSFS */
>  
> +	/* Hold back the KOBJ_ADD uevent until the device is discoverable
> +	 * by name.

nit: maybe just say "until the device is listed" ?
Or there's some less than obvious relevance of the name lookup 
vs ifindex lookup?

> +	 */
> +	dev_set_uevent_suppress(dev, 1);
> +
>  	error = device_add(dev);
>  	if (error)
>  		return error;
> @@ -2349,6 +2354,17 @@ int netdev_register_kobject(struct net_device *ndev)
>  	return error;
>  }
>  
> +/* Announce a fully registered device to userspace. This pairs with the uevent
> + * suppression from netdev_register_kobject();

nit: s/;/./ ?

> + */
> +void netdev_uevent_add(struct net_device *ndev)
> +{
> +	struct device *dev = &ndev->dev;
> +
> +	dev_set_uevent_suppress(dev, 0);
> +	kobject_uevent(&dev->kobj, KOBJ_ADD);
> +}

Please wait for Clashiko to cross-review before posting v2.
-- 
pw-bot: cr