On 22 May 2014 16:54, Johannes Berg <johannes@xxxxxxxxxxxxxxxx> wrote: > On Thu, 2014-05-22 at 16:07 +0200, Michal Kazior wrote: >> Channel switch finalization is now 2-step. First >> step is when driver calls csa_finish(), the other >> is when reservation is actually finalized (which >> be defered for in-place reservation). >> >> It is now safe to call ieee80211_csa_finish() more >> then once. > > 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. 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. Michał -- 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
