Hi
On Mon, May 12, 2014 at 8:43 PM, Felix Fietkau <n...@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).
Thanks
David
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