linux-kernel - Re: [PATCH] thermal: tegra: delete unneeded of_node

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Message-ID: <66e7906c-9472-4fcb-7c04-750bb27d3989@nvidia.com>
Date:   Mon, 17 Jul 2017 14:47:14 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Julia Lawall <Julia.Lawall@...6.fr>,
        Zhang Rui <rui.zhang@...el.com>
CC:     <kernel-janitors@...r.kernel.org>,
        Eduardo Valentin <edubezval@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        <linux-pm@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] thermal: tegra: delete unneeded of_node_put


On 15/07/17 09:42, Julia Lawall wrote:
> Device node iterators perform an of_node_put on each iteration, so putting
> an of_node_put before a continue results in a double put.
> 
> The semantic match that finds this problem is as follows
> (http://coccinelle.lip6.fr):
> 
> // <smpl>
> @@
> expression e1;
> local idexpression child;
> iterator name for_each_child_of_node;
> @@
> 
>  for_each_child_of_node(e1,child) {
>    ... when != of_node_get(child)
> *  of_node_put(child);
>    ...
> *  continue;
> }
> // </smpl>
> 
> Furthermore, the call to thermal_of_cooling_device_register immediately
> calls __thermal_cooling_device_register with the same arguments.  The
> latter function stores the device node argument, which is the second
> argument of for_each_child_of_node, in the returned thermal_cooling_device
> structure.  This returned structure is then stored in the cdev field of
> stc.  Thus it seems that the second argument of for_each_child_of_node
> escapes the scope of the for_each_child_of_node, so an explicit of_node_get
> on success of thermal_of_cooling_device_register is also needed.
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@...6.fr>
> 
> ---
>  drivers/thermal/tegra/soctherm.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/thermal/tegra/soctherm.c b/drivers/thermal/tegra/soctherm.c
> index 7d2db23..10f4fdd 100644
> --- a/drivers/thermal/tegra/soctherm.c
> +++ b/drivers/thermal/tegra/soctherm.c
> @@ -1014,7 +1014,6 @@ static void soctherm_init_hw_throt_cdev(struct platform_device *pdev)
>  		tcd = thermal_of_cooling_device_register(np_stcc,
>  							 (char *)name, ts,
>  							 &throt_cooling_ops);
> -		of_node_put(np_stcc);
>  		if (IS_ERR_OR_NULL(tcd)) {
>  			dev_err(dev,
>  				"throttle-cfg: %s: failed to register cooling device\n",
> @@ -1022,6 +1021,7 @@ static void soctherm_init_hw_throt_cdev(struct platform_device *pdev)
>  			continue;
>  		}
>  
> +		of_node_get(np_stcc);
>  		stc->cdev = tcd;
>  		stc->init = true;
>  	}

Thanks for fixing this. However, I am wondering if it is better for the
'of_node_get' to be placed within the
thermal_of_cooling_device_register() function as it seems a bit odd if
the caller needs to know that this is being stored for later use.

Also, taking a quick look, I see a couple other drivers calling
thermal_of_cooling_device_register() and they are also not calling
of_node_get on success. So it maybe easier to fix placing it in the
thermal_of_cooling_device_register() function.

Cheers
Jon

-- 
nvpublic