Hi Paul, I'm debugging a problem for a user (Florian) (http://bugzilla.intellinuxwireless.org/show_bug.cgi?id=2363) that turns out to be a mac80211 bug in 3.4, apparently introduced by an interaction between your commit commit 3117bbdb7899d43927c8ce4fe885ab7c1231c121 Author: Paul Stewart <pstew@xxxxxxxxxxxx> Date: Tue Mar 13 07:46:18 2012 -0700 mac80211: Don't let regulatory make us deaf and Rajkumar's commit commit 7cc44ed48d0ec0937c1f098642540b6c9ca38de5 Author: Rajkumar Manoharan <rmanohar@xxxxxxxxxxxxxxxx> Date: Fri Sep 16 15:32:34 2011 +0530 mac80211: Fix regression on queue stop during 2040 bss change The problem is that the code looks like this in 3.4, after both commits: if (beacon_htcap_ie && (prev_chantype != rx_channel_type)) { /* * Whenever the AP announces the HT mode change that can be * 40MHz intolerant or etc., it would be safer to stop tx * queues before doing hw config to avoid buffer overflow. */ ieee80211_stop_queues_by_reason(&sdata->local->hw, IEEE80211_QUEUE_STOP_REASON_CHTYPE_CHANGE); /* flush out all packets */ synchronize_net(); drv_flush(local, false); } /* channel_type change automatically detected */ ieee80211_hw_config(local, 0); if (prev_chantype != tx_channel_type) { rcu_read_lock(); sta = sta_info_get(sdata, bssid); if (sta) rate_control_rate_update(local, sband, sta, IEEE80211_RC_HT_CHANGED, tx_channel_type); rcu_read_unlock(); if (beacon_htcap_ie) ieee80211_wake_queues_by_reason(&sdata->local->hw, IEEE80211_QUEUE_STOP_REASON_CHTYPE_CHANGE); } In the tracing I got from Florian, I see that the AP is constantly switching between HT20 and HT40-. At some point, all this switching leads to all queues remaining stopped -- forever. The module has to be unloaded & reloaded for this to get fixed because the CHTYPE_CHANGE stop reason is never cleared and thus we never transmit any packets again. Clearly, the problem is that in the first if, we check beacon_htcap_ie as well as "prev_chantype != rx_channel_type", and in the second if that would wake the queues, it's "prev_chantype != tx_channel_type". Since RX and TX channel type can differ (which was the point of your commit), this can lead to queues being woken that weren't stopped (which is not a problem) or queues being stopped and never woken again (major issue). Now, the reason I'm writing all this in an email and not a commit log is that I don't know what the TX/RX channel type usage should be, or if maybe it should be "if (queues_stopped) wake_queues()" or something like that... Can you tell me what it should be? Thanks, 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
