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Date:   Thu, 07 Dec 2023 09:37:03 +0100
From:   Dragan Simic <dsimic@manjaro.org>
To:     Jensen Huang <jensenhuang@friendlyarm.com>
Cc:     Heiko Stuebner <heiko@sntech.de>,
        Andi Shyti <andi.shyti@kernel.org>,
        linux-arm-kernel@lists.infradead.org,
        linux-rockchip@lists.infradead.org, linux-i2c@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Dmitry Osipenko <dmitry.osipenko@collabora.com>,
        Chris Morgan <macroalpha82@gmail.com>,
        Benjamin Bara <bbara93@gmail.com>
Subject: Re: [PATCH v2] i2c: rk3x: fix potential spinlock recursion on poll
In-Reply-To: <20231207082200.16388-1-jensenhuang@friendlyarm.com>
References: <20231207082200.16388-1-jensenhuang@friendlyarm.com>
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On 2023-12-07 09:21, Jensen Huang wrote:
> Possible deadlock scenario (on reboot):
> rk3x_i2c_xfer_common(polling)
>     -> rk3x_i2c_wait_xfer_poll()
>         -> rk3x_i2c_irq(0, i2c);
>             --> spin_lock(&i2c->lock);
>             ...
>         <rk3x i2c interrupt>
>         -> rk3x_i2c_irq(0, i2c);
>             --> spin_lock(&i2c->lock); (deadlock here)
> 
> Store the IRQ number and disable/enable it around the polling transfer.
> This patch has been tested on NanoPC-T4.

In case you haven't already seen the related discussion linked below, 
please have a look.  I also added more people to the list of recipients, 
in an attempt to make everyone aware of the different approaches to 
solving this issue.

https://lore.kernel.org/all/655177f4.050a0220.d85c9.3ba0@mx.google.com/T/#m6fc9c214452fec6681843e7f455978c35c6f6c8b

> Signed-off-by: Jensen Huang <jensenhuang@friendlyarm.com>
> Reviewed-by: Heiko Stuebner <heiko@sntech.de>
> Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
> ---
> Changes in v2:
>  - Add description for member 'irq' to fix build warning
> 
>  drivers/i2c/busses/i2c-rk3x.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-rk3x.c 
> b/drivers/i2c/busses/i2c-rk3x.c
> index a044ca0c35a1..4362db7c5789 100644
> --- a/drivers/i2c/busses/i2c-rk3x.c
> +++ b/drivers/i2c/busses/i2c-rk3x.c
> @@ -178,6 +178,7 @@ struct rk3x_i2c_soc_data {
>   * @clk: function clk for rk3399 or function & Bus clks for others
>   * @pclk: Bus clk for rk3399
>   * @clk_rate_nb: i2c clk rate change notify
> + * @irq: irq number
>   * @t: I2C known timing information
>   * @lock: spinlock for the i2c bus
>   * @wait: the waitqueue to wait for i2c transfer
> @@ -200,6 +201,7 @@ struct rk3x_i2c {
>  	struct clk *clk;
>  	struct clk *pclk;
>  	struct notifier_block clk_rate_nb;
> +	int irq;
> 
>  	/* Settings */
>  	struct i2c_timings t;
> @@ -1087,13 +1089,18 @@ static int rk3x_i2c_xfer_common(struct
> i2c_adapter *adap,
> 
>  		spin_unlock_irqrestore(&i2c->lock, flags);
> 
> -		rk3x_i2c_start(i2c);
> -
>  		if (!polling) {
> +			rk3x_i2c_start(i2c);
> +
>  			timeout = wait_event_timeout(i2c->wait, !i2c->busy,
>  						     msecs_to_jiffies(WAIT_TIMEOUT));
>  		} else {
> +			disable_irq(i2c->irq);
> +			rk3x_i2c_start(i2c);
> +
>  			timeout = rk3x_i2c_wait_xfer_poll(i2c);
> +
> +			enable_irq(i2c->irq);
>  		}
> 
>  		spin_lock_irqsave(&i2c->lock, flags);
> @@ -1310,6 +1317,8 @@ static int rk3x_i2c_probe(struct platform_device 
> *pdev)
>  		return ret;
>  	}
> 
> +	i2c->irq = irq;
> +
>  	platform_set_drvdata(pdev, i2c);
> 
>  	if (i2c->soc_data->calc_timings == rk3x_i2c_v0_calc_timings) {