linux-kernel - Re: [PATCH] drm/imagination: Move dereference after NULL check in pvr_mmu_backing_page

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Message-ID: <48c059b9542fb453998dd77a676d2ce08fefdd4f.camel@imgtec.com>
Date:   Wed, 6 Dec 2023 14:42:17 +0000
From:   Frank Binns <Frank.Binns@...tec.com>
To:     Donald Robson <Donald.Robson@...tec.com>,
        "dan.carpenter@...aro.org" <dan.carpenter@...aro.org>
CC:     "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
        "tzimmermann@...e.de" <tzimmermann@...e.de>,
        Matt Coster <Matt.Coster@...tec.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "airlied@...il.com" <airlied@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sarah Walker <Sarah.Walker@...tec.com>,
        "maarten.lankhorst@...ux.intel.com" 
        <maarten.lankhorst@...ux.intel.com>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "mripard@...nel.org" <mripard@...nel.org>
Subject: Re: [PATCH] drm/imagination: Move dereference after NULL check in
 pvr_mmu_backing_page_init()

Hi Dan,

Thank you for the patch.

On Wed, 2023-12-06 at 17:37 +0300, Dan Carpenter wrote:
> This code dereferences "page->pvr_dev" and then checked for NULL on the
> next line.  Re-order it to avoid a potential NULL pointer dereference.
> 
> Fixes: ff5f643de0bf ("drm/imagination: Add GEM and VM related code")
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>

Reviewed-by: Frank Binns <frank.binns@...tec.com>

> ---
>  drivers/gpu/drm/imagination/pvr_mmu.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/imagination/pvr_mmu.c b/drivers/gpu/drm/imagination/pvr_mmu.c
> index c8562bfc0dcd..4fe70610ed94 100644
> --- a/drivers/gpu/drm/imagination/pvr_mmu.c
> +++ b/drivers/gpu/drm/imagination/pvr_mmu.c
> @@ -316,12 +316,14 @@ pvr_mmu_backing_page_init(struct pvr_mmu_backing_page *page,
>  static void
>  pvr_mmu_backing_page_fini(struct pvr_mmu_backing_page *page)
>  {
> -	struct device *dev = from_pvr_device(page->pvr_dev)->dev;
> +	struct device *dev;
>  
>  	/* Do nothing if no allocation is present. */
>  	if (!page->pvr_dev)
>  		return;
>  
> +	dev = from_pvr_device(page->pvr_dev)->dev;
> +
>  	dma_unmap_page(dev, page->dma_addr, PVR_MMU_BACKING_PAGE_SIZE,
>  		       DMA_TO_DEVICE);
>