Re: Panic with wifi + usb in latest FreeBSD-current

On Sun, Sep 13, 2020 at 11:31 PM Adrian Chadd <adrian.chadd_at_gmail.com>
wrote:

> On Sun, 13 Sep 2020 at 22:34, Warner Losh <imp_at_bsdimp.com> wrote:
>
> >
> >
> > On Sun, Sep 13, 2020, 11:29 PM Adrian Chadd <adrian.chadd_at_gmail.com>
> > wrote:
> >
> >> Yeah, this was also reported in #freebsd-wireless today.
> >>
> >> Is there a lock being held in the rtwn path that shouldn't be?
> >>
> >
> > I'll check in the morning... this was like the 20th thing to go wrong
> this
> > weekend,  so I copied the panic down, send the email and grabbed a beer
> and
> > turned it off...
> >
>
> Ok. I checked the driver and the usb stack; nothing in the change lists
> obviously stands out to me at 11pm on a Sunday.
>
> Can you see if any locks are held? or an epoch? Something smells fishy.
> (defining EPOCH_TRACE will dump the list of epochs, if I'm reading the
> subr_sleepqueue.c code correctly.)
>
> Ok, so, since I dug a bit more on a hunch, I bet the NET epoch is being
> held - it's grabbed in rtwn_bulk_rx_callback, and rtwn_rx_common is reading
> some registers as part of processing the receive queue. I bet that act of
> reading registers over blocking USB is causing things to explode.
>
> If it is net epoch then we're going to have to think of a better design
> pattern here to migrate all of these here wifi drivers to, because I
> guarantee you they're all behaving poorly in this newer world order.
>
>
>
> Thanks,
>
>
> -adrian
>
While I have not seen panics, performance of my rtwn has simply cratered.
Trying to move files to my new laptop, which has an rtwn, it crawls at
about 1.5 Mbps. Before I built an updated kernel, I was seeing 60M. Of
course, this is complicated by the continual kernel lockups I keep getting,
so I really didn't think much about it until I saw Warner's note.
--
Kevin Oberman, Part time kid herder and retired Network Engineer
E-mail: rkoberman_at_gmail.com
PGP Fingerprint: D03FB98AFA78E3B78C1694B318AB39EF1B055683