netdev - Re: [PATCH] drivers/net/can/spi/mcp251x.c: Fix race condition on receive interrupt

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Date:   Wed, 3 Aug 2022 18:48:57 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Sebastian Würl <sebastian.wuerl@...ratech.com>
Cc:     Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        "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>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, linux-can@...r.kernel.org,
        netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers/net/can/spi/mcp251x.c: Fix race condition on
 receive interrupt

On Wed, Aug 3, 2022 at 5:36 PM Sebastian Würl
<sebastian.wuerl@...ratech.com> wrote:
>
> The mcp251x driver uses both receiving mailboxes of the can controller

CAN

> chips. For retrieving the CAN frames from the controller via SPI, it checks
> once per interrupt which mailboxes have been filled, an will retrieve the
> messages accordingly.
>
> This introduces a race condition, as another CAN frame can enter mailbox 1
> while mailbox 0 is emptied. If now another CAN frame enters mailbox 0 until
> the interrupt handler is called next, mailbox 0 is emptied before
> mailbox 1, leading to out-of-order CAN frames in the network device.
>
> This is fixed by checking the interrupt flags once again after freeing
> mailbox 0, to correctly also empty mailbox 1 before leaving the handler.
>
> For reproducing the bug I created the following setup:
>  - Two CAN devices, one Raspberry Pi with MCP2515, the other can be any.
>  - Setup CAN to 1 MHz
>  - Spam bursts of 5 CAN-messages with increasing CAN-ids
>  - Continue sending the bursts while sleeping a second between the bursts
>  - Check on the RPi whether the received messages have increasing CAN-ids
>  - Without this patch, every burst of messages will contain a flipped pair

Fixes tag?

-- 
With Best Regards,
Andy Shevchenko