Johannes,
it seems I've encountered a bug in mac80211 RX aggregation handler.
The hw is a pair of stations using AR9580 (PCI ID 168c:0033) PCIe
adapters. Linux 5.4-rc4.
The driver shows the chip is Atheros AR9300 Rev:4.
I'm using (on both ends):
iw wlan0 set type ibss
ip link set wlan0 up
iw dev wlan0 ibss join $ESSID $FREQ HT20
The problem manifests itself after one of the stations is restarted
(or the ath9k driver is reloaded, or a station is out of range for
some time etc).
It appears that the mac80211 RX aggregation code sets a new aggregation
"session" at the remote station's request, but the head_seq_num
(the sequence number the receiver expects to receive) isn't reset.
I've added some debugging code to ___ieee80211_start_rx_ba_session()
and ieee80211_sta_manage_reorder_buf() and it produced the following:
Both stations boot and join the IBSS, packets get through:
[ 61.123131] AGG RX OK: ssn 1
[ 61.125346] SEQ OK: 1 vs 1
[ 61.125484] SEQ OK: 2 vs 2
[ 62.100841] SEQ OK: 3 vs 3
...
[ 180.124210] SEQ OK: 130 vs 130
[ 181.123888] SEQ OK: 131 vs 131
[ 182.126046] SEQ OK: 132 vs 132
Now I'm rebooting the remote station. It joins IBSS, packets can be seen
on mon0 monitoring interface (on the local station), but they aren't
arriving on wlan0:
[ 192.131102] SEQ BAD: 0 vs 133
[ 192.151243] AGG RX no change - OK: ssn 1
[ 192.242760] SEQ BAD: 1 vs 133
[ 193.133819] SEQ BAD: 2 vs 133
[ 193.272802] SEQ BAD: 3 vs 133
...
[ 421.272374] SEQ BAD: 130 vs 133
[ 421.303630] SEQ BAD: 131 vs 133
[ 422.327924] SEQ BAD: 132 vs 133
Then the sequence number catches up and the communication is
reestablished:
[ 423.167023] SEQ OK: 133 vs 133
[ 423.169061] SEQ OK: 134 vs 134
[ 423.351618] SEQ OK: 135 vs 135
I'll attach a patch in a separate mail but I'm not sure if it's
the optimal fix - one packet (the "SEQ BAD: 0 vs 133) is still dropped,
and I guess it won't work if the sender decides to not request
aggregation anymore.
Comments?
The debugging code:
--- a/net/mac80211/agg-rx.c
+++ b/net/mac80211/agg-rx.c
@@ -354,9 +354,10 @@ void ___ieee80211_start_rx_ba_session(struct sta_info *sta,
*/
rcu_read_lock();
tid_rx = rcu_dereference(sta->ampdu_mlme.tid_rx[tid]);
- if (tid_rx && tid_rx->timeout == timeout)
+ if (tid_rx && tid_rx->timeout == timeout) {
status = WLAN_STATUS_SUCCESS;
- else
+ printk(KERN_DEBUG "AGG RX no change - OK: ssn %u\n", start_seq_num);
+ } else
status = WLAN_STATUS_REQUEST_DECLINED;
rcu_read_unlock();
goto end;
@@ -434,6 +437,7 @@ void ___ieee80211_start_rx_ba_session(struct sta_info *sta,
tid_agg_rx->tid = tid;
tid_agg_rx->sta = sta;
status = WLAN_STATUS_SUCCESS;
+ printk(KERN_DEBUG "AGG RX OK: ssn %u\n", start_seq_num);
/* activate it for RX */
rcu_assign_pointer(sta->ampdu_mlme.tid_rx[tid], tid_agg_rx);
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -1298,9 +1298,11 @@ static bool ieee80211_sta_manage_reorder_buf(struct ieee80211_sub_if_data *sdata
/* frame with out of date sequence number */
if (ieee80211_sn_less(mpdu_seq_num, head_seq_num)) {
+ printk(KERN_DEBUG "SEQ BAD: %u vs %u\n", mpdu_seq_num, head_seq_num);
dev_kfree_skb(skb);
goto out;
- }
+ } else
+ printk(KERN_DEBUG "SEQ OK: %u vs %u\n", mpdu_seq_num, head_seq_num);
/*
* If frame the sequence number exceeds our buffering window
--
Krzysztof Hałasa
ŁUKASIEWICZ Research Network
Industrial Research Institute for Automation and Measurements PIAP
Al. Jerozolimskie 202, 02-486 Warsaw, Poland
