Re: [PATCH] usb: cdc-wdm: close race between read and workqueue

[Oliver Neukum]

On 15.04.24 11:26, Bjørn Mork wrote:
> Oliver Neukum <oneukum@xxxxxxxx> writes:
> > On 15.04.24 08:47, Bjørn Mork wrote:
> >
> > > urb from service_outstanding_interrupt(). That's why it was added. See
> > > the explanation Robert wrote when introducing it:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/usb/class/cdc-wdm.c?id=c1da59dad0ebd3f9bd238f3fff82b1f7ffda7829
> >
> > Well, the explanation is correct in that we must read
> > data available. However, if the RESPONDING flag is set
> > and the URB submitted, we are already doing so.
>
> Sounds reasonable.  Except that the bug proves we didn't.

Why? I am afraid I do not get that part.
 
> If you are right that service_outstanding_interrupt can race againts
> itself (and I don't doubt that), then I guess this could also happen
> between failure to submit the URB and clearing the flag?

Yes, it can. In fact in this case the behavior should not change.
I am afraid we have a misunderstanding. It seems to me that in the
unchanged driver the result of service_outstanding_interrupt()
is undefined.
Please explain.

	Regards
		Oliver