linux-kernel - Re: [PATCH v2] ARM: imx: fix error handling

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Message-ID: <20140516193139.GQ16662@pengutronix.de>
Date:	Fri, 16 May 2014 21:31:39 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	walter harms <wharms@....de>
Cc:	Emil Goode <emilgoode@...il.com>,
	Shawn Guo <shawn.guo@...escale.com>,
	Sascha Hauer <kernel@...gutronix.de>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH v2] ARM: imx: fix error handling

Hello Walter,

On Fri, May 16, 2014 at 01:49:10PM +0200, walter harms wrote:
> Am 16.05.2014 13:16, schrieb Emil Goode:
> > Hello Walter,
> > 
> > On Fri, May 16, 2014 at 12:40:19PM +0200, walter harms wrote:
> >>
> >>
> >> Am 16.05.2014 11:54, schrieb Emil Goode:
> >>> If we fail to allocate struct platform_device pdev we
> >>> dereference it after the goto label err.
> >>>
> >>> I have rearranged the error handling a bit to fix the issue
> >>> and also make it more clear.
> >>>
> >>> Signed-off-by: Emil Goode <emilgoode@...il.com>
> >>> ---
> >>> v2: Changed to return -ENOMEM instead of ret where possible and
> >>>     updated the subject line.
> >>>
> >>>  arch/arm/mach-imx/devices/platform-ipu-core.c |   22 +++++++++++++---------
> >>>  1 file changed, 13 insertions(+), 9 deletions(-)
> >>>
> >>> diff --git a/arch/arm/mach-imx/devices/platform-ipu-core.c b/arch/arm/mach-imx/devices/platform-ipu-core.c
> >>> index fc4dd7c..68f2a4a 100644
> >>> --- a/arch/arm/mach-imx/devices/platform-ipu-core.c
> >>> +++ b/arch/arm/mach-imx/devices/platform-ipu-core.c
> >>> @@ -77,34 +77,38 @@ struct platform_device *__init imx_alloc_mx3_camera(
> >>>  
> >>>  	pdev = platform_device_alloc("mx3-camera", 0);
> >>>  	if (!pdev)
> >>> -		goto err;
> >>> +		return ERR_PTR(-ENOMEM);
> >>>  
> >>>  	pdev->dev.dma_mask = kmalloc(sizeof(*pdev->dev.dma_mask), GFP_KERNEL);
> >>>  	if (!pdev->dev.dma_mask)
> >>> -		goto err;
> >>> +		goto put_pdev;
> >>>  
> >>>  	*pdev->dev.dma_mask = DMA_BIT_MASK(32);
> >>>  	pdev->dev.coherent_dma_mask = DMA_BIT_MASK(32);
> >>>  
> >>>  	ret = platform_device_add_resources(pdev, res, ARRAY_SIZE(res));
> >>>  	if (ret)
> >>> -		goto err;
> >>> +		goto free_dma_mask;
> >>>  
> >>>  	if (pdata) {
> >>>  		struct mx3_camera_pdata *copied_pdata;
> >>>  
> >>>  		ret = platform_device_add_data(pdev, pdata, sizeof(*pdata));
> >>> -		if (ret) {
> >>> -err:
> >>> -			kfree(pdev->dev.dma_mask);
> >>> -			platform_device_put(pdev);
> >>> -			return ERR_PTR(-ENODEV);
> >>> -		}
> >>> +		if (ret)
> >>> +			goto free_dma_mask;
> >>> +
> >>>  		copied_pdata = dev_get_platdata(&pdev->dev);
> >>>  		copied_pdata->dma_dev = &imx_ipu_coredev->dev;
> >>
> >>
> >> the patch is fine, but what use is this copied_pdata ?
> >> It scope ends next line ?
> >>
> >> re,
> >>  wh
> > 
> > I also thought that looked a bit odd, but copied_pdata is a temporary
> > pointer to platform_data of the dev struct.
> > 
> > dev_get_platdata looks like this:
> > 
> > static inline void *dev_get_platdata(const struct device *dev)
> > {
> >         return dev->platform_data;
> > }
> > 
> > So I believe it's a more compact way of writing:
> > 
> > pdev->dev->platform_data->dma_dev = &imx_ipu_coredev->dev;
It's not about compactness. The dev_get_platdata accessor exists to be
used instead of directly accessing dev->platform_data. I admit a comment
would be nice ...

Anyhow this is all ugly, actually you'd want to have the dma_dev member
already fixed when calling platform_device_add_data. But you cannot
simply do

	pdata->dma_dev = &imx_ipu_coredev->dev;
	ret = platform_device_add_data(pdev, pdata, sizeof(*pdata));

because *pdata is const.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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