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

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Date:   Tue, 29 Oct 2019 09:41:35 +0100
From:   Koen Vandeputte <koen.vandeputte@...ntric.com>
To:     Johannes Berg <johannes@...solutions.net>,
        Krzysztof Hałasa <khalasa@...p.pl>
Cc:     "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] 802.11n IBSS: wlan0 stops receiving packets due to
 aggregation after sender reboot


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@...p.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