[Make-wifi-fast] [PATCH v7] mac80211: Move reorder-sensitive TX handlers to after TXQ dequeue.

[Toke Høiland-Jørgensen]

Toke Høiland-Jørgensen <toke at toke.dk> writes:

> The TXQ intermediate queues can cause packet reordering when more than
> one flow is active to a single station. Since some of the wifi-specific
> packet handling (notably sequence number and encryption handling) is
> sensitive to re-ordering, things break if they are applied before the
> TXQ.
>
> This splits up the TX handlers and fast_xmit logic into two parts: An
> early part and a late part. The former is applied before TXQ enqueue,
> and the latter after dequeue. The non-TXQ path just applies both parts
> at once.
>
> Because fragments shouldn't be split up or reordered, the fragmentation
> handler is run after dequeue. Any fragments are then kept in the TXQ and
> on subsequent dequeues they take precedence over dequeueing from the FQ
> structure.
>
> This approach avoids having to scatter special cases for when TXQ is
> enabled, at the cost of making the fast_xmit and TX handler code
> slightly more complex.
>
> Signed-off-by: Toke Høiland-Jørgensen <toke at toke.dk>
> ---
> Changes since v6:
>   - Invoking the rate control handler can cause packets to be generated
>     (for establishing a BA session). This can cause a deadlock because
>     dequeue can happen while sta->lock is held. So this version moves
>     the rate control handler back before the intermediate queue step.
>   - Fix sequence number allocation on the slow path.

Attaching a version suitable for dropping into a LEDE build (where it
replaces 220-fq_disable_hack.patch and
346-mac80211-fix-sequence-number-assignment-for-PS-respo.patch).

-Toke

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