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

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Date:   Mon, 26 Apr 2021 08:28:40 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Oleksandr Natalenko <oleksandr@...alenko.name>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        LKML <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 <intel-wired-lan@...ts.osuosl.org>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [igb] netconsole triggers warning in netpoll_poll_dev

On Sun, Apr 25, 2021 at 11:47 PM Oleksandr Natalenko
<oleksandr@...alenko.name> wrote:
>
> Hello.
>
> On Fri, Apr 23, 2021 at 03:58:36PM -0700, Jakub Kicinski wrote:
> > On Fri, 23 Apr 2021 10:19:44 +0200 Oleksandr Natalenko wrote:
> > > On Wed, Apr 07, 2021 at 04:06:29PM -0700, Alexander Duyck wrote:
> > > > On Wed, Apr 7, 2021 at 11:07 AM Jakub Kicinski <kuba@...nel.org> wrote:
> > > > > 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.
> > >
> > > So, among all the variants, which one to try? Or there was a separate
> > > patch sent to address this?
> >
> > Alex's suggestion is probably best.
> >
> > I'm not aware of the fix being posted. Perhaps you could take over and
> > post the patch if Intel doesn't chime in?
>
> So, IIUC, Alex suggests this:
>
> ```
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
> index a45cd2b416c8..7503d5bf168a 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -7981,7 +7981,7 @@ static int igb_poll(struct napi_struct *napi, int budget)
>                                                      struct igb_q_vector,
>                                                      napi);
>         bool clean_complete = true;
> -       int work_done = 0;
> +       unsigned int work_done = 0;
>
>  #ifdef CONFIG_IGB_DCA
>         if (q_vector->adapter->flags & IGB_FLAG_DCA_ENABLED)
> @@ -8008,7 +8008,7 @@ static int igb_poll(struct napi_struct *napi, int budget)
>         if (likely(napi_complete_done(napi, work_done)))
>                 igb_ring_irq_enable(q_vector);
>
> -       return min(work_done, budget - 1);
> +       return min_t(unsigned int, work_done, budget - 1);
>  }
>
>  /**
> ```
>
> Am I right?
>
> Thanks.

Actually a better way to go would be to probably just initialize
"clean_complete = !!budget". With that we don't have it messing with
the interrupt enables which would probably be a better behavior.