linux-kernel - Re: Possible race condition of the rockchip

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Message-ID: <20250919-lurking-agama-of-genius-96b832-mkl@pengutronix.de>
Date: Fri, 19 Sep 2025 21:03:59 +0200
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Andrea Daoud <andreadaoud6@...il.com>
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

Hello,

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.

> 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 :/

regards,
Marc 

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
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