Re: [PATCH net] net: wireless: intel: iwlwifi: fix GRO_NORMAL packet stalling

From: Luciano Coelho <luciano.coelho@intel.com>
To: Alexander Lobakin <alobakin@dlink.ru>,
	"David S. Miller" <davem@davemloft.net>
Cc: Edward Cree <ecree@solarflare.com>,
	Jiri Pirko <jiri@mellanox.com>,
	Eric Dumazet <edumazet@google.com>,
	Ido Schimmel <idosch@mellanox.com>,
	Paolo Abeni <pabeni@redhat.com>,
	Petr Machata <petrm@mellanox.com>,
	Sabrina Dubroca <sd@queasysnail.net>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Jassi Brar <jaswinder.singh@linaro.org>,
	Manish Chopra <manishc@marvell.com>,
	GR-Linux-NIC-Dev@marvell.com,
	Johannes Berg <johannes.berg@intel.com>,
	Emmanuel Grumbach <emmanuel.grumbach@intel.com>,
	Intel Linux Wireless <linuxwifi@intel.com>,
	Kalle Valo <kvalo@codeaurora.org>,
	Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>,
	"Kenneth R. Crudup" <kenny@panix.com>,
	netdev@vger.kernel.org, linux-wireless@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH net] net: wireless: intel: iwlwifi: fix GRO_NORMAL packet stalling
Date: Wed, 27 Nov 2019 11:58:33 +0200	[thread overview]
Message-ID: <7a9332bf645fbb8c9fff634a3640c092fb9b4b79.camel@intel.com> (raw)
In-Reply-To: <20191127094123.18161-1-alobakin@dlink.ru>

On Wed, 2019-11-27 at 12:41 +0300, Alexander Lobakin wrote:
> 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@dlink.ru>
> ---

We don't usually use "net: wireless: intel:" in the commit message, we
would use "iwlwifi: pcie:", but I don't care much.

Otherwise:

Acked-by: Luca Coelho <luciano.coelho@intel.com>

Thanks a lot for the fix!

Dave, I'm assuming you'll take this directly into your tree, right?

--
Cheers,
Luca.