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

Alexander Lobakin
2019-11-27T16:31:31Z

Edward Cree wrote 27.11.2019 19:05:
> On 27/11/2019 09:41, 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>
> Reviewed-by: Edward Cree <ecree@solarflare.com>

Thanks! And you were the first who's found the root of the issue.

Regards,
ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ