RE: [Intel-wired-lan] [PATCH v2] idpf: increment completion queue next_to_clean in sw marker wait routine

[Loktionov, Aleksandr]

> -----Original Message-----
> From: Li Li <boolli@xxxxxxxxxx>
> Sent: Monday, January 5, 2026 8:49 AM
> To: Loktionov, Aleksandr <aleksandr.loktionov@xxxxxxxxx>
> Cc: Nguyen, Anthony L <anthony.l.nguyen@xxxxxxxxx>; Kitszel,
> Przemyslaw <przemyslaw.kitszel@xxxxxxxxx>; David S. Miller
> <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Eric Dumazet
> <edumazet@xxxxxxxxxx>; intel-wired-lan@xxxxxxxxxxxxxxxx;
> netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; David Decotigny
> <decot@xxxxxxxxxx>; Singhai, Anjali <anjali.singhai@xxxxxxxxx>;
> Samudrala, Sridhar <sridhar.samudrala@xxxxxxxxx>; Brian Vazquez
> <brianvv@xxxxxxxxxx>; Tantilov, Emil S <emil.s.tantilov@xxxxxxxxx>
> Subject: Re: [Intel-wired-lan] [PATCH v2] idpf: increment completion
> queue next_to_clean in sw marker wait routine
> 
> On Sun, Jan 4, 2026 at 11:43 PM Loktionov, Aleksandr
> <aleksandr.loktionov@xxxxxxxxx> wrote:
> >
> >
> >
> >
> >
> > From: Li Li <boolli@xxxxxxxxxx>
> > Sent: Monday, January 5, 2026 8:39 AM
> > To: Loktionov, Aleksandr <aleksandr.loktionov@xxxxxxxxx>
> > Cc: Nguyen, Anthony L <anthony.l.nguyen@xxxxxxxxx>; Kitszel,
> > Przemyslaw <przemyslaw.kitszel@xxxxxxxxx>; David S. Miller
> > <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Eric
> Dumazet
> > <edumazet@xxxxxxxxxx>; intel-wired-lan@xxxxxxxxxxxxxxxx;
> > netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; David
> Decotigny
> > <decot@xxxxxxxxxx>; Singhai, Anjali <anjali.singhai@xxxxxxxxx>;
> > Samudrala, Sridhar <sridhar.samudrala@xxxxxxxxx>; Brian Vazquez
> > <brianvv@xxxxxxxxxx>; Tantilov, Emil S <emil.s.tantilov@xxxxxxxxx>
> > Subject: Re: [Intel-wired-lan] [PATCH v2] idpf: increment completion
> > queue next_to_clean in sw marker wait routine
> >
> >
> >
> >
> >
> >
> >
> > On Sun, Jan 4, 2026 at 11:19 PM Loktionov, Aleksandr
> <aleksandr.loktionov@xxxxxxxxx> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Intel-wired-lan <intel-wired-lan-bounces@xxxxxxxxxx> On
> Behalf
> > > Of Li Li via Intel-wired-lan
> > > Sent: Monday, January 5, 2026 7:47 AM
> > > To: Nguyen, Anthony L <anthony.l.nguyen@xxxxxxxxx>; Kitszel,
> > > Przemyslaw <przemyslaw.kitszel@xxxxxxxxx>; David S. Miller
> > > <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Eric
> > > Dumazet <edumazet@xxxxxxxxxx>; intel-wired-lan@xxxxxxxxxxxxxxxx
> > > Cc: netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; David
> > > Decotigny <decot@xxxxxxxxxx>; Singhai, Anjali
> > > <anjali.singhai@xxxxxxxxx>; Samudrala, Sridhar
> > > <sridhar.samudrala@xxxxxxxxx>; Brian Vazquez <brianvv@xxxxxxxxxx>;
> > > Tantilov, Emil S <emil.s.tantilov@xxxxxxxxx>; Li Li
> > > <boolli@xxxxxxxxxx>
> > > Subject: [Intel-wired-lan] [PATCH v2] idpf: increment completion
> > > queue next_to_clean in sw marker wait routine
> > >
> > > Currently, in idpf_wait_for_sw_marker_completion(), when an
> > > IDPF_TXD_COMPLT_SW_MARKER packet is found, the routine breaks out
> of
> > > the for loop and does not increment the next_to_clean counter.
> This
> > > causes the subsequent NAPI polls to run into the same
> > > IDPF_TXD_COMPLT_SW_MARKER packet again and print out the
> following:
> > >
> > >     [   23.261341] idpf 0000:05:00.0 eth1: Unknown TX completion
> type:
> > > 5
> > >
> > > Instead, we should increment next_to_clean regardless when an
> > > IDPF_TXD_COMPLT_SW_MARKER packet is found.
> > >
> > > Tested: with the patch applied, we do not see the errors above
> from
> > > NAPI polls anymore.
> > >
> > > Signed-off-by: Li Li <boolli@xxxxxxxxxx>
> > > ---
> > > Changes in v2:
> > >  - Initialize idpf_tx_queue *target to NULL to suppress the
> "'target'
> > >    uninitialized when 'if' statement is true warning".
> > >
> > >  drivers/net/ethernet/intel/idpf/idpf_txrx.c | 6 +++---
> > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> > > b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> > > index 69bab7187e541..452d0a9e83a4f 100644
> > > --- a/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> > > +++ b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> > > @@ -2326,7 +2326,7 @@ void
> idpf_wait_for_sw_marker_completion(const
> > > struct idpf_tx_queue *txq)
> > >
> > >       do {
> > >               struct idpf_splitq_4b_tx_compl_desc *tx_desc;
> > > -             struct idpf_tx_queue *target;
> > > +             struct idpf_tx_queue *target = NULL;
> > Linux kernel is against premature initialization just to silence a
> compiler.
> > The target variable is dereferenced at idpf_queue_clear(SW_MARKER,
> > target)) but can remain uninitialized if execution jumps to the
> next:
> > label via a goto before target is assigned.
> > Isn't it?
> >
> > That is correct. When the following if statement (line 2341-2343)
> evaluates to true:
> >
> >
> >
> >   if (FIELD_GET(IDPF_TXD_COMPLQ_COMPL_TYPE_M, ctype_gen) !=
> >    IDPF_TXD_COMPLT_SW_MARKER)
> >     goto next;
> >
> >
> >
> > Then the initialization at line 2346:
> >
> >
> >
> >   target = complq->txq_grp->txqs[id];
> >
> >
> >
> > would be skipped, making "target" uninitialized.
> >
> >
> >
> > Therefore, in this patch, I need to initialize "target" to NULL.
> >
> >
> >
> > The ‘NULL’ target variable can be dereferenced at
> idpf_queue_clear(SW_MARKER, target)), isn’t it?
> 
> That would not be possible, because right before
> "idpf_queue_clear(SW_MARKER, target))", "target"
> is initialized to "complq->txq_grp->txqs[id]":
> 
>   if (FIELD_GET(IDPF_TXD_COMPLQ_COMPL_TYPE_M, ctype_gen) !=
>     IDPF_TXD_COMPLT_SW_MARKER)
>     goto next;
> 
>   id = FIELD_GET(IDPF_TXD_COMPLQ_QID_M, ctype_gen);
>   target = complq->txq_grp->txqs[id];
> 
>   idpf_queue_clear(SW_MARKER, target);
> 
> "target" only remains uninitialized if the if statement above
> evaluates to true and skips the initialization.
> 
> >
> >
> >
> >
> >
> >
> > >               u32 ctype_gen, id;
> > >
> > >               tx_desc = flow ? &complq->comp[ntc].common :
> > > @@ -2346,14 +2346,14 @@ void
> > > idpf_wait_for_sw_marker_completion(const
> > > struct idpf_tx_queue *txq)
> > >               target = complq->txq_grp->txqs[id];
> > >
> > >               idpf_queue_clear(SW_MARKER, target);
> > > -             if (target == txq)
> > > -                     break;
> > >
> > >  next:
> > >               if (unlikely(++ntc == complq->desc_count)) {
> > >                       ntc = 0;
> > >                       gen_flag = !gen_flag;
> > >               }
> > > +             if (target == txq)
> > Are tou sure that incremented ntc value is ever written back to
> complq->next_to_clean?
> >
> >
> >
> > Yes, the value of "ntc" is written back to "complq->next_to_clean"
> at
> > the end of the function
> >
> >  (at line 2360):
> >
> >
> >
> >   complq->next_to_clean = ntc;
> >
> > Thank you, I don’t see it from the patch.
> >
> >
> >
> >
> > > +                     break;
> > >       } while (time_before(jiffies, timeout));
> > >
> > >       idpf_queue_assign(GEN_CHK, complq, gen_flag);
> > > --
> > > 2.52.0.351.gbe84eed79e-goog

Thank you for the clarifications
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@xxxxxxxxx>