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Date:   Wed, 3 Aug 2022 18:48:57 +0200
From:   Andy Shevchenko <>
To:     Sebastian Würl <>
Cc:     Wolfgang Grandegger <>,
        Marc Kleine-Budde <>,
        "David S. Miller" <>,
        Eric Dumazet <>,
        Jakub Kicinski <>,
        Paolo Abeni <>,
        Vincent Mailhol <>,
        Stefan Mätje <>,
        Andy Shevchenko <>,
        Oliver Hartkopp <>,
        Sebastian Andrzej Siewior <>,
        Uwe Kleine-König 
        netdev <>,
        Linux Kernel Mailing List <>
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
<> wrote:
> The mcp251x driver uses both receiving mailboxes of the can controller


> 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

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