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 11:51:40 +0100
From:   khalasa@...p.pl (Krzysztof Hałasa)
To:     Johannes Berg <johannes@...solutions.net>
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

Johannes Berg <johannes@...solutions.net> writes:

>> The problem I can see is that the dialog_tokens are 8-bit, way too small
>> to eliminate conflicts.
>
> Well, they're also per station, we could just randomize the start and
> then we'd delete the old session and start a new one, on the receiver.
>
> So that would improve robustness somewhat (down to a 1/256 chance to hit
> this problem).

That was what I meant. Still, 1/256 seems hardly acceptable to me -
unless there is some work around (a short timeout or something similar).
Remember that when it doesn't work, it doesn't work - it won't recover
until the sequence catches up, which may mean basically forever.

Or, maybe the remote station can request de-aggregation first, so the
subsequent aggregation request is always treated as new?

Alternatively, perhaps the remote can signal that it's a new request and
not merely an existing session?

> That's the situation though - the local station needs to know that it
> has in fact *not* seen the same instance of the station, but that the
> station has reset and needs to be removed & re-added.

Precisely. And it seems to me that the first time the local station
learns of this is when a new, regular, non-aggregated packet arrives.
Or, when a new aggregation request arrives.
-- 
Krzysztof Halasa

ŁUKASIEWICZ Research Network
Industrial Research Institute for Automation and Measurements PIAP
Al. Jerozolimskie 202, 02-486 Warsaw, Poland