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From:   Eric Dumazet <edumazet@google.com>
Date:   Mon, 9 Oct 2023 10:27:32 +0200
Message-ID: <CANn89iLLsM8=fqoa_7O8iYyCzT2ebNs_jpY+e-RW+xCc7UnSDg@mail.gmail.com>
Subject: Re: [net-next PATCH v2 4/4] netdev: use napi_schedule bool instead of napi_schedule_prep/__napi_schedule
To:     Christian Marangi <ansuelsmth@gmail.com>
Cc:     Jason Gunthorpe <jgg@ziepe.ca>, Leon Romanovsky <leon@kernel.org>,
        Wolfgang Grandegger <wg@grandegger.com>,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Chris Snook <chris.snook@gmail.com>,
        Raju Rangoju <rajur@chelsio.com>,
        Jeroen de Borst <jeroendb@google.com>,
        Praveen Kaligineedi <pkaligineedi@google.com>,
        Shailend Chand <shailend@google.com>,
        Douglas Miller <dougmill@linux.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Nick Child <nnac123@linux.ibm.com>,
        Haren Myneni <haren@linux.ibm.com>,
        Rick Lindsley <ricklind@linux.ibm.com>,
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        Loic Poulain <loic.poulain@linaro.org>,
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        <u.kleine-koenig@pengutronix.de>, Wei Fang <wei.fang@nxp.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        Yuri Karpov <YKarpov@ispras.ru>,
        Zhengchao Shao <shaozhengchao@huawei.com>,
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        linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org,
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On Sun, Oct 8, 2023 at 8:27=E2=80=AFPM Christian Marangi <ansuelsmth@gmail.=
com> wrote:
>
> On Sun, Oct 08, 2023 at 09:08:41AM +0200, Eric Dumazet wrote:
> > On Fri, Oct 6, 2023 at 8:49=E2=80=AFPM Christian Marangi <ansuelsmth@gm=
ail.com> wrote:
> > >
> > > On Thu, Oct 05, 2023 at 06:16:26PM +0200, Eric Dumazet wrote:
> > > > On Tue, Oct 3, 2023 at 8:36=E2=80=AFPM Christian Marangi <ansuelsmt=
h@gmail.com> wrote:
> > > > >
> > > > > Replace if condition of napi_schedule_prep/__napi_schedule and us=
e bool
> > > > > from napi_schedule directly where possible.
> > > > >
> > > > > Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
> > > > > ---
> > > > >  drivers/net/ethernet/atheros/atlx/atl1.c     | 4 +---
> > > > >  drivers/net/ethernet/toshiba/tc35815.c       | 4 +---
> > > > >  drivers/net/wireless/intel/iwlwifi/pcie/rx.c | 4 +---
> > > > >  3 files changed, 3 insertions(+), 9 deletions(-)
> > > > >
> > > > > diff --git a/drivers/net/ethernet/atheros/atlx/atl1.c b/drivers/n=
et/ethernet/atheros/atlx/atl1.c
> > > > > index 02aa6fd8ebc2..a9014d7932db 100644
> > > > > --- a/drivers/net/ethernet/atheros/atlx/atl1.c
> > > > > +++ b/drivers/net/ethernet/atheros/atlx/atl1.c
> > > > > @@ -2446,7 +2446,7 @@ static int atl1_rings_clean(struct napi_str=
uct *napi, int budget)
> > > > >
> > > > >  static inline int atl1_sched_rings_clean(struct atl1_adapter* ad=
apter)
> > > > >  {
> > > > > -       if (!napi_schedule_prep(&adapter->napi))
> > > > > +       if (!napi_schedule(&adapter->napi))
> > > > >                 /* It is possible in case even the RX/TX ints are=
 disabled via IMR
> > > > >                  * register the ISR bits are set anyway (but do n=
ot produce IRQ).
> > > > >                  * To handle such situation the napi functions us=
ed to check is
> > > > > @@ -2454,8 +2454,6 @@ static inline int atl1_sched_rings_clean(st=
ruct atl1_adapter* adapter)
> > > > >                  */
> > > > >                 return 0;
> > > > >
> > > > > -       __napi_schedule(&adapter->napi);
> > > > > -
> > > > >         /*
> > > > >          * Disable RX/TX ints via IMR register if it is
> > > > >          * allowed. NAPI handler must reenable them in same
> > > > > diff --git a/drivers/net/ethernet/toshiba/tc35815.c b/drivers/net=
/ethernet/toshiba/tc35815.c
> > > > > index 14cf6ecf6d0d..a8b8a0e13f9a 100644
> > > > > --- a/drivers/net/ethernet/toshiba/tc35815.c
> > > > > +++ b/drivers/net/ethernet/toshiba/tc35815.c
> > > > > @@ -1436,9 +1436,7 @@ static irqreturn_t tc35815_interrupt(int ir=
q, void *dev_id)
> > > > >         if (!(dmactl & DMA_IntMask)) {
> > > > >                 /* disable interrupts */
> > > > >                 tc_writel(dmactl | DMA_IntMask, &tr->DMA_Ctl);
> > > > > -               if (napi_schedule_prep(&lp->napi))
> > > > > -                       __napi_schedule(&lp->napi);
> > > > > -               else {
> > > > > +               if (!napi_schedule(&lp->napi)) {
> > > > >                         printk(KERN_ERR "%s: interrupt taken in p=
oll\n",
> > > > >                                dev->name);
> > > > >                         BUG();
> > > >
> > > > Hmmm... could you also remove this BUG() ? I think this code path c=
an be taken
> > > > if some applications are using busy polling.
> > > >
> > > > Or simply rewrite this with the traditional
> > > >
> > > > if (napi_schedule_prep(&lp->napi)) {
> > > >    /* disable interrupts */
> > > >    tc_writel(dmactl | DMA_IntMask, &tr->DMA_Ctl);
> > > >     __napi_schedule(&lp->napi);
> > > > }
> > > >
> > > >
> > >
> > > Mhhh is it safe to do so? I mean it seems very wrong to print a warni=
ng
> > > and BUG() instead of disabling the interrupt only if napi can be
> > > scheduled... Maybe is very old code? The more I see this the more I s=
ee
> > > problem... (randomly disabling the interrupt and then make the kernel
> > > die)
> >
> > I am pretty sure this BUG() can be hit these days with busy polling or
> > setting gro_flush_timeout.
> >
> > I wish we could remove these bugs before someone copy-paste them.
> >
> > Again, this is orthogonal, I might simply stop doing reviews if this
> > is not useful.
>
> They are very useful and thanks a lot for them! I'm asking these as to
> understand how to proceed. I have in queue 2 other series that depends
> on this and I'm just asking info on how to speedup the progress on this!
>
> Soo think I have to send v3 with the suggested change and BUG() dropped?
> Happy to do everything to fix and improve this series!

I think that your patch series is all about doing cleanups,
so I suggested adding another cleanup/fix,
and this can be done independently.

I doubt this matters, this code has probably not been used for quite a
long time...