Re: [PATCH] drm/imagination: fix off by one in pvr_vm_mips_init() error handling

[Frank Binns <Frank.Binns@imgtec.com>]

On Thu, 2023-11-30 at 10:27 +0300, Dan Carpenter wrote:
> If the call to vmap() fails the "page_nr" is one element beyond the end
> of the mips_data->pt_dma_addr[] and mips_data->pt_pages[] arrays.
> 
> The way that this is traditionally written is that we clean up the
> partial loop iteration before the goto and then we can say
> while (--i >= 0).  At that point we know that all the elements thus
> far are initialized so we don't need to have NULL checks.
> 
> Fixes: 927f3e0253c1 ("drm/imagination: Implement MIPS firmware processor and MMU support")
> Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>

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

> ---
>  drivers/gpu/drm/imagination/pvr_vm_mips.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/imagination/pvr_vm_mips.c b/drivers/gpu/drm/imagination/pvr_vm_mips.c
> index 7268cf6e630b..2bc7181a4c3e 100644
> --- a/drivers/gpu/drm/imagination/pvr_vm_mips.c
> +++ b/drivers/gpu/drm/imagination/pvr_vm_mips.c
> @@ -57,6 +57,7 @@ pvr_vm_mips_init(struct pvr_device *pvr_dev)
>  							       PAGE_SIZE, DMA_TO_DEVICE);
>  		if (dma_mapping_error(dev, mips_data->pt_dma_addr[page_nr])) {
>  			err = -ENOMEM;
> +			__free_page(mips_data->pt_pages[page_nr]);
>  			goto err_free_pages;
>  		}
>  	}
> @@ -79,13 +80,11 @@ pvr_vm_mips_init(struct pvr_device *pvr_dev)
>  	return 0;
>  
>  err_free_pages:
> -	for (; page_nr >= 0; page_nr--) {
> -		if (mips_data->pt_dma_addr[page_nr])
> -			dma_unmap_page(from_pvr_device(pvr_dev)->dev,
> -				       mips_data->pt_dma_addr[page_nr], PAGE_SIZE, DMA_TO_DEVICE);
> +	while (--page_nr >= 0) {
> +		dma_unmap_page(from_pvr_device(pvr_dev)->dev,
> +			       mips_data->pt_dma_addr[page_nr], PAGE_SIZE, DMA_TO_DEVICE);
>  
> -		if (mips_data->pt_pages[page_nr])
> -			__free_page(mips_data->pt_pages[page_nr]);
> +		__free_page(mips_data->pt_pages[page_nr]);
>  	}
>  
>  	return err;