net: Defer netdev KOBJ_ADD uevent until the device is published

net: Defer netdev KOBJ_ADD uevent until the device is published

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")
Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Shahar Shitrit <shshitrit@nvidia.com>
Link: https://patch.msgid.link/20260806080758.2039586-2-dtatulea@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>