linux-kernel - Re: [igb] netconsole triggers warning in netpoll_poll

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Date:   Wed, 7 Apr 2021 16:06:29 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Oleksandr Natalenko <oleksandr@...alenko.name>,
        linux-kernel@...r.kernel.org,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org
Subject: Re: [igb] netconsole triggers warning in netpoll_poll_dev

On Wed, Apr 7, 2021 at 11:07 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Wed, 7 Apr 2021 09:25:28 -0700 Alexander Duyck wrote:
> > On Wed, Apr 7, 2021 at 8:37 AM Jakub Kicinski <kuba@...nel.org> wrote:
> > >
> > > On Wed, 7 Apr 2021 08:00:53 +0200 Oleksandr Natalenko wrote:
> > > > Thanks for the effort, but reportedly [1] it made no difference,
> > > > unfortunately.
> > > >
> > > > [1] https://bugzilla.kernel.org/show_bug.cgi?id=212573#c8
> > >
> > > The only other option I see is that somehow the NAPI has no rings.
> > >
> > > diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
> > > index a45cd2b416c8..24568adc2fb1 100644
> > > --- a/drivers/net/ethernet/intel/igb/igb_main.c
> > > +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> > > @@ -7980,7 +7980,7 @@ static int igb_poll(struct napi_struct *napi, int budget)
> > >         struct igb_q_vector *q_vector = container_of(napi,
> > >                                                      struct igb_q_vector,
> > >                                                      napi);
> > > -       bool clean_complete = true;
> > > +       bool clean_complete = q_vector->tx.ring || q_vector->rx.ring;
> > >         int work_done = 0;
> > >
> > >  #ifdef CONFIG_IGB_DCA
> >
> > It might make sense to just cast the work_done as a unsigned int, and
> > then on the end of igb_poll use:
> >   return min_t(unsigned int, work_done, budget - 1);
>
> Sure, that's simplest. I wasn't sure something is supposed to prevent
> this condition or if it's okay to cover it up.

I'm pretty sure it is okay to cover it up. In this case the "budget -
1" is supposed to be the upper limit on what can be reported. I think
it was assuming an unsigned value anyway.

Another alternative would be to default clean_complete to !!budget.
Then if budget is 0 clean_complete would always return false.