Re: [PATCH] net: usbnet: Avoid potential RCU stall on LINK_CHANGE event

Hi Jakub,

On 7/15/25 1:35 AM, Jakub Kicinski wrote:

On Thu, 10 Jul 2025 08:50:40 +0000 John Ernberg wrote:

quoted

Having a Gemalto Cinterion PLS83-W modem attached to USB and activating the
cellular data link would sometimes yield the following RCU stall, leading
to a system freeze:

Do you know which sub-driver it's using?

The modem uses cdc_ether (and option for the TTYs).

I'm worried that this is still racy.
Since usbnet_bh checks if carrier is ok and __handle_link_change()
checks the opposite something must be out of sync if both run.
Most likely something restored the carrier while we're still handling
the previous carrier loss.

There could definitely be other factors, I'll try to dig some in 
cdc_ether and see if something there could be causing problems for the 
usbnet core.
I honestly kinda stopped digging when I found unlink_urbs() being 
wrapped with a pause/unpause at another place tied to a commit seeing a 
similar issue.

Thanks! // John Ernberg