Re: [PATCH net] net: lapbether: Prevent racing when checking whether the netif is running

[Jakub Kicinski]

On Wed, 10 Mar 2021 23:23:09 -0800 Xie He wrote:
> There are two "netif_running" checks in this driver. One is in
> "lapbeth_xmit" and the other is in "lapbeth_rcv". They serve to make
> sure that the LAPB APIs called in these functions are called before
> "lapb_unregister" is called by the "ndo_stop" function.
> 
> However, these "netif_running" checks are unreliable, because it's
> possible that immediately after "netif_running" returns true, "ndo_stop"
> is called (which causes "lapb_unregister" to be called).
> 
> This patch adds locking to make sure "lapbeth_xmit" and "lapbeth_rcv" can
> reliably check and ensure the netif is running while doing their work.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Xie He <xie.he.0141@xxxxxxxxx>

Is this a theoretical issues or do you see a path where it triggers?

Who are the callers sending frames to a device which went down?