netdev - Re: Possible race condition of the rockchip

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Message-ID: <CAOprWott046xznChj7JBNmVw3Z65uOC1_bqTbVB=LA+YBw7TTQ@mail.gmail.com>
Date: Sat, 20 Sep 2025 18:08:03 +0800
From: Andrea Daoud <andreadaoud6@...il.com>
To: Marc Kleine-Budde <mkl@...gutronix.de>
Cc: Heiko Stuebner <heiko@...ech.de>, Elaine Zhang <zhangqing@...k-chips.com>, kernel@...gutronix.de, 
	linux-can@...r.kernel.org, netdev@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: Possible race condition of the rockchip_canfd driver

On Sat, Sep 20, 2025 at 3:04 AM Marc Kleine-Budde <mkl@...gutronix.de> wrote:
>
> Hello,

Thanks for your reply!

>
> On 18.09.2025 20:58:33, Andrea Daoud wrote:
> > I'm using the rockchip_canfd driver on an RK3568. When under high bus
> > load, I get
> > the following logs [1] in rkcanfd_tx_tail_is_eff, and the CAN bus is unable to
> > communicate properly under this condition. The exact cause is currently not
> > entirely clear, and it's not reliably reproducible.
>
> Our customer is using a v3 silicon revision of the chip, which doesn't
> this workaround.

Could you please let me know how to check whether my RK3568 is v2 or v3?

>
> > In the logs we can spot some strange points:
> >
> > 1. Line 24, tx_head == tx_tail. This should have been rejected by the if
> > (!rkcanfd_get_tx_pending) clause.
> >
> > 2. Line 26, the last bit of priv->tx_tail (0x0185dbb3) is 1. This means that the
> > tx_tail should be 1, because rkcanfd_get_tx_tail is essentially mod the
> > priv->tx_tail by two. But the printed tx_tail is 0.
> >
> > I believe these problems could mean that the code is suffering from some race
> > condition. It seems that, in the whole IRQ processing chain of the driver,
> > there's no lock protection. Maybe some IRQ happens within the execution of
> > rkcanfd_tx_tail_is_eff, and touches the state of the tx_head and tx_tail?
> >
> > Could you please have a look at the code, and check if some locking is needed?
>
> My time for community support is currently a bit limited. I think this
> has to wait a bit, apologies :/

No worries, I will debug myself, and hopefully send a PR if I found
something out.

>
> regards,
> Marc
>
> --
> Pengutronix e.K.                 | Marc Kleine-Budde          |
> Embedded Linux                   | https://www.pengutronix.de |
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Regards,
Andrea