linux-kernel - Re: [PATCH v3] video: fbdev: vesafb: add missed release

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Message-ID: <1f5e6f52-c638-f73e-cf9d-88eb641a010d@samsung.com>
Date:   Fri, 20 Mar 2020 13:01:09 +0100
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:     Chuhong Yuan <hslester96@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] video: fbdev: vesafb: add missed release_region


On 3/10/20 3:35 AM, Chuhong Yuan wrote:
> The driver forgets to free the I/O region in remove and probe
> failure.
> Add the missed calls to fix it.
> 
> Signed-off-by: Chuhong Yuan <hslester96@...il.com>
> ---
> Changes in v3:
>   - Revise the commit message.
>   - Add an error handler to suit the "goto error" before request_region().
>   - Revise the order of operations in remove.
>   
>  drivers/video/fbdev/vesafb.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/video/fbdev/vesafb.c b/drivers/video/fbdev/vesafb.c
> index a1fe24ea869b..c7bc9ace47d4 100644
> --- a/drivers/video/fbdev/vesafb.c
> +++ b/drivers/video/fbdev/vesafb.c
> @@ -439,7 +439,7 @@ static int vesafb_probe(struct platform_device *dev)
>  		       "vesafb: abort, cannot ioremap video memory 0x%x @ 0x%lx\n",
>  			vesafb_fix.smem_len, vesafb_fix.smem_start);
>  		err = -EIO;
> -		goto err;
> +		goto err_release_region;
>  	}
>  
>  	printk(KERN_INFO "vesafb: framebuffer at 0x%lx, mapped to 0x%p, "
> @@ -458,15 +458,17 @@ static int vesafb_probe(struct platform_device *dev)
>  
>  	if (fb_alloc_cmap(&info->cmap, 256, 0) < 0) {
>  		err = -ENOMEM;
> -		goto err;
> +		goto err_release_region;
>  	}
>  	if (register_framebuffer(info)<0) {
>  		err = -EINVAL;
>  		fb_dealloc_cmap(&info->cmap);
> -		goto err;
> +		goto err_release_region;
>  	}
>  	fb_info(info, "%s frame buffer device\n", info->fix.id);
>  	return 0;
> +err_release_region:
> +	release_region(0x3c0, 32);

This is incorrect.

The cleanup order should be the reverse of the probing order.

Also request_region() return value is not checked by the driver
(there is a comment that it can fail and is optional):

        /* request failure does not faze us, as vgacon probably has this
         * region already (FIXME) */
        request_region(0x3c0, 32, "vesafb");

so what would happen in such case? It seems that unconditionally
doing the release will result in freeing the I/O region owned by
the other driver (vgacon)..

>  err:
>  	arch_phys_wc_del(par->wc_cookie);
>  	if (info->screen_base)
> @@ -481,6 +483,7 @@ static int vesafb_remove(struct platform_device *pdev)
>  	struct fb_info *info = platform_get_drvdata(pdev);
>  
>  	unregister_framebuffer(info);
> +	release_region(0x3c0, 32);
>  	framebuffer_release(info);
>  
>  	return 0;
> 
 
Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics