On Fri, 2014-05-23 at 08:49 +0200, Michal Kazior wrote: > > But you'll WARN_ON() if they're actually not at the same time and you > > grab a beacon (or for the template case, call csa_update) in the > > meantime, right? I'd really like to have all those driver requirements > > (e.g. to stop beaconing) better documented. > > Good point. I suppose it should be stated in the docs that once you > reach ieee80211_csa_is_complete() being true you must not call > ieee80211_beacon_get() nor ieee80211_csa_update_counter(). ath9k and > ath10k conform to this. Right, it's still a bit strange that you just have to stop beaconing. Dunno. I guess I don't care all that much since our driver won't support multiple AP interfaces anyway :-) > I wonder what driver should be supposed to look at before starting to > beacon again? csa_active isn't well protected to be depended upon. If > we should create a ieee80211_csa_is_active() that just checks if > beacon->csa_counter_offset[0] != 0 (assuming my other csa counter > patches are applied) then it's still racy: > a) rcu_dereference() across ieee80211_csa_is_active(), _is_complete() > and _beacon_get() can yield different beacon pointers > b) cs_count <= 1 yields no beacon update (thus no counters/offsets, > meaning both _csa_is_complete and _csa_is_active() are `false` thus > suggesting driver can beacon as if nothing happened) > > We could fix (b) by simply not treating cs_count <= 1 so special and > update the beacon anyway. For (a) to work we'd need either make a > single-call do-all function or introduce an additional call and a > generic pointer/structure to be passed to other functions so that a > beacon pointer is consistent across calls. You could technically just return NULL in this period, but I don't know how well drivers would cope with that (though technically they have to cope with it due to memory allocation failures anyway) johannes -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
