On Tue, May 13, 2014 at 11:09:48AM +0200, David Herrmann wrote:
> Hi
> 
> On Tue, May 13, 2014 at 11:00 AM, Rajkumar Manoharan
> <rmanohar@qti.qualcomm.com> wrote:
> > On Tue, May 13, 2014 at 08:50:00AM +0200, David Herrmann wrote:
> >> Hi
> >>
> >> On Mon, May 12, 2014 at 8:43 PM, Felix Fietkau <nbd@openwrt.org> wrote:
> >> > I looked into it again, the scenario where I assumed that this problem
> >> > could occur didn't turn out to be true. I have no idea how this crash
> >> > can occur.
> >>
> >> The only path that can set ah->caldata to NULL is through:
> >>
> >> ieee80211_hw_config()
> >>   ath9k_htc_config()
> >>     ath9k_htc_set_channel()
> >>       ath9k_hw_reset()
> >>
> >> This happens whenever IEEE80211_CONF_OFFCHANNEL is set.
> >>
> >> Now mac80211 is way to big for me to review right now and
> >> ieee80211_hw_config() is used quite often. Given that the described
> >> call-path does no synchronization against ath9k_htc_ani_work(), all
> >> the callers of mac80211_hw_config(OFFCHANNEL) must guarantee that no
> >> ani-work is running. Is that intentional? I cannot see any of those
> >> functions calling into ath9k_htc_stop_ani(). This might of course be
> >> implicit.
> >>
> >> One call-path I see is:
> >> ieee80211_scan_cancel()
> >>   cancel_delayed_work()
> >>
> >> We cannot use cancel_delayed_work_sync() here due to locking issues.
> >> However, this obviously races against any following
> >> set_channel(OFFCHANNEL) request.
> >>
> >> If there's anything I can do to debug this, let me know. I tried
> >> adding some printk()'s into the hot-path and it turns out to no longer
> >> fail then. So this really seems to be a quite small race (given that a
> >> bunch of simple printk()s is slow enough to work around it).
> >
> > David,
> >
> > Are you using USB devices? What is the PID/VID? I have not looked at
> > HTC driver perspective.
> 
> Yes, I'm using the htc driver. I thought that was clear by pointing at
> ar9002, but I was wrong, sorry. lsusb information is:
>   'Bus 003 Device 056: ID 0411:017f BUFFALO INC. (formerly MelCo.,
> Inc.) Sony UWA-BR100 802.11abgn Wireless Adapter [Atheros
> AR7010+AR9280]'
>
Unlike ath9k driver, the ani work is stopped in sw_scan_start callback
for htc driver. So during scan process, ani work is stopped well before
calling set_channel. But in case of p2p_listen operation, set_channel can be
called by sw_roc without stopping ani.

Can you please test with attached change?

-Rajkumar