Subject: Re: [PATCH] ethtool: don't touch the parent device of a net device being unregistered

From: Jakub Kicinski <[email-masked]>
Date: Mon, 23 Mar 2026 15:08:27 -0700

On Mon, 23 Mar 2026 02:08:53 +0300 Alexander Popov wrote:
> Hello Andrew, let me describe the scenario that I see:
> 
>   - The netdev_run_todo() function handles the net devices in net_todo_list
>     in a loop and moves each of them into the NETREG_UNREGISTERED state:
>       netdev_lock(dev);
>       WRITE_ONCE(dev->reg_state, NETREG_UNREGISTERED);
>       netdev_unlock(dev);
> 
>   - Then netdev_run_todo() frees these net devices in another loop.
>     On each iteration, it chooses a device for freeing:
>       dev = netdev_wait_allrefs_any(&list);
> 
>   - At the same time, the ethnl_set_features() function calls
>     ethnl_parse_header_dev_get() for the child net device.
> 
>   - If the race condition succeeds, ethnl_set_features() takes the reference
>     to the child net device being unregistered. That makes netdev_run_todo()
>     free the parent first.

That's not sufficient detail. ethnl_parse_header_dev_get() is under RCU
and unregistration does an RCU sync after delisting the device. Also
not sure you're distinguishing struct net_device and struct device.

How did you hit this issue? What are the net devices involved?