Re: [PATCHv2 net] usbnet: fix cyclical race on disconnect with work queue

[Oliver Neukum]

On 11.09.24 00:44, Jakub Kicinski wrote:

Hi,
 
> I have sort of an inverse question to what Paolo asked :)

This is getting interesting.

> AFAIU we need the double-cancel because checking the flag and
> scheduling are not atomic. But if we do that why the memory

Right.

> barriers? They make it seem like we're doing something clever
> with memory ordering, while really we're just depending on normal
> properties of the tasklet/timer/work APIs.

Good question. I added this because they are used in usbnet_defer_kevent()
which can be used in hard irq context. Are you saying I should check
whether this is actually needed?

> FTR disable_work_sync() would work nicely here but it'd be
> a PITA for backports.

So should I use it?
 
> Also - is this based on some report or syzbot? I'm a bit tempted
> to put this in net-next given how unlikely the race is vs how
> commonly used the driver is.

Having found the thing with the random MAC I decided to look
closely at the driver for overlooked stuff.

	Regards
		Oliver