Re: [igb] netconsole triggers warning in netpoll_poll_dev

[Danielle Ratson <danieller@nvidia.com>]

> On Thu, May 6, 2021 at 4:32 PM Jesse Brandeburg
> <jesse.brandeburg@intel.com> wrote:
> >
> > Alexander Duyck wrote:
> >
> > > On Sun, Apr 25, 2021 at 11:47 PM Oleksandr Natalenko
> > > <oleksandr@natalenko.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@kernel.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.
> >
> >
> > Thanks guys for the suggestions here! Finally got some time for this,
> > so here is the patch I'm going to queue shortly.
> >
> > From ffd24e90d688ee347ab051266bfc7fca00324a68 Mon Sep 17 00:00:00
> 2001
> > From: Jesse Brandeburg <jesse.brandeburg@intel.com>
> > Date: Thu, 6 May 2021 14:41:11 -0700
> > Subject: [PATCH net] igb: fix netpoll exit with traffic
> > To: netdev,
> >     Oleksandr Natalenko <oleksandr@natalenko.name>
> > Cc: Jakub Kicinski <kuba@kernel.org>, LKML
> > <linux-kernel@vger.kernel.org>, "Brandeburg, Jesse"
> > <jesse.brandeburg@intel.com>, "Nguyen, Anthony L"
> > <anthony.l.nguyen@intel.com>, "David S. Miller"
> <davem@davemloft.net>,
> > intel-wired-lan <intel-wired-lan@lists.osuosl.org>, Alexander Duyck
> > <alexander.duyck@gmail.com>
> >
> > Oleksandr brought a bug report where netpoll causes trace messages in
> > the log on igb.
> >
> > [22038.710800] ------------[ cut here ]------------ [22038.710801]
> > igb_poll+0x0/0x1440 [igb] exceeded budget in poll [22038.710802]
> > WARNING: CPU: 12 PID: 40362 at net/core/netpoll.c:155
> > netpoll_poll_dev+0x18a/0x1a0
> >
> > After some discussion and debug from the list, it was deemed that the
> > right thing to do is initialize the clean_complete variable to false
> > when the "netpoll mode" of passing a zero budget is used.
> >
> > This logic should be sane and not risky because the only time budget
> > should be zero on entry is netpoll.  Change includes a small refactor
> > of local variable assignments to clean up the look.
> >
> > Fixes: 16eb8815c235 ("igb: Refactor clean_rx_irq to reduce overhead
> > and improve performance")
> > Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name>
> > Suggested-by: Alexander Duyck <alexander.duyck@gmail.com>
> > Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
> > ---
> >
> > Compile tested ONLY, but functionally it should be exactly the same
> > for all cases except when budget is zero on entry, which will
> > hopefully fix the bug.
> > ---
> >  drivers/net/ethernet/intel/igb/igb_main.c | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/intel/igb/igb_main.c
> > b/drivers/net/ethernet/intel/igb/igb_main.c
> > index 0cd37ad81b4e..b0a9bed14071 100644
> > --- a/drivers/net/ethernet/intel/igb/igb_main.c
> > +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> > @@ -7991,12 +7991,16 @@ static void igb_ring_irq_enable(struct
> igb_q_vector *q_vector)
> >   **/
> >  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;
> > +       struct igb_q_vector *q_vector;
> > +       bool clean_complete;
> >         int work_done = 0;
> >
> > +       /* if budget is zero, we have a special case for netconsole, so
> > +        * make sure to set clean_complete to false in that case.
> > +        */
> > +       clean_complete = !!budget;
> > +
> > +       q_vector = container_of(napi, struct igb_q_vector, napi);
> >  #ifdef CONFIG_IGB_DCA
> >         if (q_vector->adapter->flags & IGB_FLAG_DCA_ENABLED)
> >                 igb_update_dca(q_vector);
> 
> I'm not a big fan of moving the q_vector init as a part of this patch since it
> just means more backport work.
> 
> That said the change itself should be harmless so I am good with it either
> way.
> 
> Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>

Hi,

I have lately added the netconsole module, and since then we see the same warning constantly in the logs.
I have tried to apply Jesse's patch but it didn't seem to solve the issue.

Did anyone managed to solve the issue and can share with us?

Thanks,
Danielle