linux-kernel - Re: [PATCH v3] serial: samsung: Checks the return value of function

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Date:   Wed, 7 Jul 2021 17:55:43 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Tamseel Shams <m.shams@...sung.com>
Cc:     krzysztof.kozlowski@...onical.com, gregkh@...uxfoundation.org,
        jirislaby@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, alim.akhtar@...sung.com
Subject: Re: [PATCH v3] serial: samsung: Checks the return value of function

On Tue, Jul 06, 2021 at 11:49:09AM +0530, Tamseel Shams wrote:

Please provide a better commit summary; "Checks the return value of
function" is too vague.

> "uart_add_one_port" function call may fail and return
> some error code, so adding a check for return value.
> If it is returning some error code, then displaying the
> result, unregistering the driver and then returning from
> probe function with error code.
> 
> Signed-off-by: Tamseel Shams <m.shams@...sung.com>
> ---
> Changes since v1:
> 1. Added support to unregister driver on failure of "uart_add_one_port"
> function call.
> 2. Commit message updated.
> 
> Changes since v2:
> 1. Added support to unwind clocks on failure of "uart_add_one_port"
> function call.
> 
>  drivers/tty/serial/samsung_tty.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c
> index 9fbc61151c2e..a3f3a17fb54b 100644
> --- a/drivers/tty/serial/samsung_tty.c
> +++ b/drivers/tty/serial/samsung_tty.c
> @@ -2253,7 +2253,11 @@ static int s3c24xx_serial_probe(struct platform_device *pdev)
>  	}
>  
>  	dev_dbg(&pdev->dev, "%s: adding port\n", __func__);
> -	uart_add_one_port(&s3c24xx_uart_drv, &ourport->port);
> +	ret = uart_add_one_port(&s3c24xx_uart_drv, &ourport->port);
> +	if (ret < 0) {
> +		dev_err(&pdev->dev, "Failed to add uart port, err %d\n", ret);
> +		goto add_port_error;
> +	}
>  	platform_set_drvdata(pdev, &ourport->port);
>  
>  	/*
> @@ -2272,6 +2276,17 @@ static int s3c24xx_serial_probe(struct platform_device *pdev)
>  	probe_index++;
>  
>  	return 0;
> +
> +add_port_error:

Name error labels after what they do, not where jump from (e.g.
"err_disable_clk").

> +	ourport->port.mapbase = 0;
> +	clk_disable_unprepare(ourport->clk);
> +	clk_put(ourport->clk);
> +	if (!IS_ERR(ourport->baudclk)) {
> +		clk_disable_unprepare(ourport->baudclk);
> +		clk_put(ourport->baudclk);
> +	}
> +	uart_unregister_driver(&s3c24xx_uart_drv);

You can't just deregister the serial driver if probe of a single port
fails. What if there are more than one port?

Looks like the driver has the same bug in remove(). What a mess... Added
by 6f134c3c7703 ("serial: samsung: Move uart_register_driver call to
device probe") in 2014.

And the clocks are never disabled and released in case
uart_register_driver() fails above either.

> +	return ret;
>  }
>  
>  static int s3c24xx_serial_remove(struct platform_device *dev)

Johan