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

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 <redacted>

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?