netdev - Re: [PATCH net] net: wireless: intel: iwlwifi: fix GRO

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Date:   Wed, 27 Nov 2019 11:23:10 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     alobakin@...nk.ru
Cc:     ecree@...arflare.com, jiri@...lanox.com, edumazet@...gle.com,
        idosch@...lanox.com, pabeni@...hat.com, petrm@...lanox.com,
        sd@...asysnail.net, f.fainelli@...il.com,
        jaswinder.singh@...aro.org, manishc@...vell.com,
        GR-Linux-NIC-Dev@...vell.com, johannes.berg@...el.com,
        emmanuel.grumbach@...el.com, luciano.coelho@...el.com,
        linuxwifi@...el.com, kvalo@...eaurora.org,
        nicholas.johnson-opensource@...look.com.au, kenny@...ix.com,
        netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: wireless: intel: iwlwifi: fix GRO_NORMAL
 packet stalling

From: Alexander Lobakin <alobakin@...nk.ru>
Date: Wed, 27 Nov 2019 12:41:23 +0300

> Commit 6570bc79c0df ("net: core: use listified Rx for GRO_NORMAL in
> napi_gro_receive()") has applied batched GRO_NORMAL packets processing
> to all napi_gro_receive() users, including mac80211-based drivers.
> 
> However, this change has led to a regression in iwlwifi driver [1][2] as
> it is required for NAPI users to call napi_complete_done() or
> napi_complete() and the end of every polling iteration, whilst iwlwifi
> doesn't use NAPI scheduling at all and just calls napi_gro_flush().
> In that particular case, packets which have not been already flushed
> from napi->rx_list stall in it until at least next Rx cycle.
> 
> Fix this by adding a manual flushing of the list to iwlwifi driver right
> before napi_gro_flush() call to mimic napi_complete() logics.
> 
> I prefer to open-code gro_normal_list() rather than exporting it for 2
> reasons:
> * to prevent from using it and napi_gro_flush() in any new drivers,
>   as it is the *really* bad way to use NAPI that should be avoided;
> * to keep gro_normal_list() static and don't lose any CC optimizations.
> 
> I also don't add the "Fixes:" tag as the mentioned commit was only a
> trigger that only exposed an improper usage of NAPI in this particular
> driver.
> 
> [1] https://lore.kernel.org/netdev/PSXP216MB04388962C411CD0B17A86F47804A0@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM
> [2] https://bugzilla.kernel.org/show_bug.cgi?id=205647
> 
> Signed-off-by: Alexander Lobakin <alobakin@...nk.ru>

Applied, thanks for the quick turnaround.