Re: [PATCH v2] 802.11n IBSS: wlan0 stops receiving packets due to aggregation after sender reboot

[Sebastian Gottschall <s.gottschall@newmedia-net.de>]

35 km? for 802.11n with ht40 this is out of the ack timing range the 
chipset supports. so this should be considered at any troubles with 
connections

Am 29.10.2019 um 09:41 schrieb Koen Vandeputte:
>
> On 28.10.19 13:21, Johannes Berg wrote:
>> On Fri, 2019-10-25 at 12:21 +0200, Krzysztof Hałasa wrote:
>>> Fix a bug where 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.
>>>
>>> Spotted on a pair of AR9580 in IBSS mode.
>>>
>>> Signed-off-by: Krzysztof Halasa <khalasa@piap.pl>
>>>
>>> diff --git a/net/mac80211/agg-rx.c b/net/mac80211/agg-rx.c
>>> index 4d1c335e06e5..67733bd61297 100644
>>> --- a/net/mac80211/agg-rx.c
>>> +++ b/net/mac80211/agg-rx.c
>>> @@ -354,10 +354,13 @@ 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) {
>>> +                tid_rx->ssn = start_seq_num;
>>> +                tid_rx->head_seq_num = start_seq_num;
>>>                   status = WLAN_STATUS_SUCCESS;
>> This is wrong, this is the case of *updating an existing session*, we
>> must not reset the head SN then.
>>
>> I think you just got very lucky (or unlucky) to have the same dialog
>> token, because we start from 0 - maybe we should initialize it to a
>> random value to flush out such issues.
>>
>> Really what I think probably happened is that one of your stations lost
>> the connection to the other, and didn't tell it about it in any way - so
>> the other kept all the status alive.
>>
>> I suspect to make all this work well we need to not only have the fixes
>> I made recently to actually send and parse deauth frames, but also to
>> even send an auth and reset the state when we receive that, so if we
>> move out of range and even the deauth frame is lost, we can still reset
>> properly.
>>
>> In any case, this is not the right approach - we need to handle the
>> "lost connection" case better I suspect, but since you don't say what
>> really happened I don't really know that that's what you're seeing.
>>
>> johannes
>
> Hi all,
>
> I can confirm the issue as I'm also seeing this sometimes in the field 
> here.
>
> Sometimes when a devices goes out of range and then re-enters,
> the link refuses to "come up", as in rx looks to be "stuck" without 
> any reports in system log or locking issues (lockdep enabled)
>
> I have dozens of devices installed offshore (802.11n based), both on 
> static and moving assets,
> which cover from short (250m) up to very long distances (~35km)
>
> So .. while there is some momentum for this issue,
> I'm more than happy to provide extensive testing should fixes be 
> posted regarding IBSS in general.
>
> Regards,
>
> Koen
>
>