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

[Jakub Kicinski]

On Thu, 11 Mar 2021 13:12:25 -0800 Xie He wrote:
> On Thu, Mar 11, 2021 at 12:43 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
> >
> > 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?  
> 
> This is a theoretical issue. I didn't see this issue in practice.
> 
> When "__dev_queue_xmit" and "sch_direct_xmit" call
> "dev_hard_start_xmit", there appears to be no locking mechanism
> preventing the netif from going down while "dev_hard_start_xmit" is
> doing its work.

Normally driver's ndo_stop() calls netif_tx_disable() which takes TX
locks, so unless your driver is lockless (LLTX) there should be no xmit
calls after that point.