linux-kernel - Re: [PATCH v4] can: mcp251x: Fix race condition on receive interrupt

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Message-ID: <CAHp75Vf8VtN5pLDLVrNGKUmq3W=gY8u9jsKX+AqR4UjmmR7zvw@mail.gmail.com>
Date:   Thu, 4 Aug 2022 20:42:19 +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>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        Stefan Mätje <stefan.maetje@....eu>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Christian Pellegrin <chripell@...e.org>,
        linux-can@...r.kernel.org, netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] can: mcp251x: Fix race condition on receive interrupt

On Thu, Aug 4, 2022 at 10:42 AM Sebastian Würl
<sebastian.wuerl@...ratech.com> 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 and 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

For future submissions...

> Fixes: bf66f3736a94 ("can: mcp251x: Move to threaded interrupts instead of workqueues.")
> Signed-off-by: Sebastian Würl <sebastian.wuerl@...ratech.com>
> ---

When you send the new version of a single patch, use --annotate to put
a changelog here (after the cutter '---' line) so people will know how
v4 differes to v3 to v2 and to v1.


Also you mentioned some issues with the mail program. Use `git
send-email` for patch submission. Also you may consider my "smart"
(no) script [1] for that.

[1]: https://github.com/andy-shev/home-bin-tools/blob/master/ge2maintainer.sh


-- 
With Best Regards,
Andy Shevchenko