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Message-ID: <IA3PR11MB8986E00F2F77A95EFB2A8C88E586A@IA3PR11MB8986.namprd11.prod.outlook.com>
Date: Mon, 5 Jan 2026 08:06:13 +0000
From: "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>
To: Li Li <boolli@...gle.com>
CC: "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>, "Kitszel, Przemyslaw"
<przemyslaw.kitszel@...el.com>, "David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "David
Decotigny" <decot@...gle.com>, "Singhai, Anjali" <anjali.singhai@...el.com>,
"Samudrala, Sridhar" <sridhar.samudrala@...el.com>, Brian Vazquez
<brianvv@...gle.com>, "Tantilov, Emil S" <emil.s.tantilov@...el.com>
Subject: RE: [Intel-wired-lan] [PATCH v2] idpf: increment completion queue
next_to_clean in sw marker wait routine
> -----Original Message-----
> From: Li Li <boolli@...gle.com>
> Sent: Monday, January 5, 2026 8:49 AM
> To: Loktionov, Aleksandr <aleksandr.loktionov@...el.com>
> Cc: Nguyen, Anthony L <anthony.l.nguyen@...el.com>; Kitszel,
> Przemyslaw <przemyslaw.kitszel@...el.com>; David S. Miller
> <davem@...emloft.net>; Jakub Kicinski <kuba@...nel.org>; Eric Dumazet
> <edumazet@...gle.com>; intel-wired-lan@...ts.osuosl.org;
> netdev@...r.kernel.org; linux-kernel@...r.kernel.org; David Decotigny
> <decot@...gle.com>; Singhai, Anjali <anjali.singhai@...el.com>;
> Samudrala, Sridhar <sridhar.samudrala@...el.com>; Brian Vazquez
> <brianvv@...gle.com>; Tantilov, Emil S <emil.s.tantilov@...el.com>
> 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@...el.com> wrote:
> >
> >
> >
> >
> >
> > From: Li Li <boolli@...gle.com>
> > Sent: Monday, January 5, 2026 8:39 AM
> > To: Loktionov, Aleksandr <aleksandr.loktionov@...el.com>
> > Cc: Nguyen, Anthony L <anthony.l.nguyen@...el.com>; Kitszel,
> > Przemyslaw <przemyslaw.kitszel@...el.com>; David S. Miller
> > <davem@...emloft.net>; Jakub Kicinski <kuba@...nel.org>; Eric
> Dumazet
> > <edumazet@...gle.com>; intel-wired-lan@...ts.osuosl.org;
> > netdev@...r.kernel.org; linux-kernel@...r.kernel.org; David
> Decotigny
> > <decot@...gle.com>; Singhai, Anjali <anjali.singhai@...el.com>;
> > Samudrala, Sridhar <sridhar.samudrala@...el.com>; Brian Vazquez
> > <brianvv@...gle.com>; Tantilov, Emil S <emil.s.tantilov@...el.com>
> > 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@...el.com> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On
> Behalf
> > > Of Li Li via Intel-wired-lan
> > > Sent: Monday, January 5, 2026 7:47 AM
> > > To: Nguyen, Anthony L <anthony.l.nguyen@...el.com>; Kitszel,
> > > Przemyslaw <przemyslaw.kitszel@...el.com>; David S. Miller
> > > <davem@...emloft.net>; Jakub Kicinski <kuba@...nel.org>; Eric
> > > Dumazet <edumazet@...gle.com>; intel-wired-lan@...ts.osuosl.org
> > > Cc: netdev@...r.kernel.org; linux-kernel@...r.kernel.org; David
> > > Decotigny <decot@...gle.com>; Singhai, Anjali
> > > <anjali.singhai@...el.com>; Samudrala, Sridhar
> > > <sridhar.samudrala@...el.com>; Brian Vazquez <brianvv@...gle.com>;
> > > Tantilov, Emil S <emil.s.tantilov@...el.com>; Li Li
> > > <boolli@...gle.com>
> > > 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@...gle.com>
> > > ---
> > > 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@...el.com>
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