netdev - Re: [PATCH 1/3] can: rcar_canfd: Fix IRQ storm on global fifo receive

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Date:   Mon, 24 Oct 2022 17:53:42 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Biju Das <biju.das.jz@...renesas.com>
Cc:     Wolfgang Grandegger <wg@...ndegger.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Stefan Mätje <stefan.maetje@....eu>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Ulrich Hecht <uli+renesas@...nd.eu>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Rob Herring <robh@...nel.org>, linux-can@...r.kernel.org,
        netdev@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH 1/3] can: rcar_canfd: Fix IRQ storm on global fifo receive

On 24.10.2022 17:37:35, Marc Kleine-Budde wrote:
> On 22.10.2022 09:15:01, Biju Das wrote:
> > We are seeing IRQ storm on global receive IRQ line under heavy CAN
> > bus load conditions with both CAN channels are enabled.
> > 
> > Conditions:
> >   The global receive IRQ line is shared between can0 and can1, either
> >   of the channels can trigger interrupt while the other channel irq
> >   line is disabled(rfie).
> >   When global receive IRQ interrupt occurs, we mask the interrupt in
> >   irqhandler. Clearing and unmasking of the interrupt is happening in
> >   rx_poll(). There is a race condition where rx_poll unmask the
> >   interrupt, but the next irq handler does not mask the irq due to
> >   NAPIF_STATE_MISSED flag.
> 
> Why does this happen? Is it a problem that you call
> rcar_canfd_handle_global_receive() for a channel that has the IRQs
> actually disabled in hardware?

Can you check if the IRQ is active _and_ enabled before handling the IRQ
on a particular channel?

A more clearer approach would be to get rid of the global interrupt
handlers at all. If the hardware only given 1 IRQ line for more than 1
channel, the driver would register an IRQ handler for each channel (with
the shared attribute). The IRQ handler must check, if the IRQ is pending
and enabled. If not return IRQ_NONE, otherwise handle and return IRQ_HANDLED.

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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