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

[Alexander Lobakin]

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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > [2] https://bugzilla.kernel.org/show_bug.cgi?id=205647
> >
> > Signed-off-by: Alexander Lobakin <alobakin@xxxxxxxx>
> Reviewed-by: Edward Cree <ecree@xxxxxxxxxxxxxx>

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

Regards,
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