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

On Thu, 11 Mar 2021 13:12:25 -0800 Xie He wrote:

On Thu, Mar 11, 2021 at 12:43 PM Jakub Kicinski [off-list ref] wrote:

quoted

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.