Re: [PATCH] drm/buddy: Fix alloc_range() error handling code

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Feb 09, 2024 at 08:56:24PM +0530, Arunpravin Paneer Selvam wrote:
> Few users have observed display corruption when they boot
> the machine to KDE Plasma or playing games. We have root
> caused the problem that whenever alloc_range() couldn't
> find the required memory blocks the function was returning
> SUCCESS in some of the corner cases.
> 
> The right approach would be if the total allocated size
> is less than the required size, the function should
> return -ENOSPC.
> 
> Cc:  <stable@vger.kernel.org> # 6.7+
> Fixes: 0a1844bf0b53 ("drm/buddy: Improve contiguous memory allocation")
> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3097
> Tested-by: Mario Limonciello <mario.limonciello@amd.com>
> Link: https://patchwork.kernel.org/project/dri-devel/patch/20240207174456.341121-1-Arunpravin.PaneerSelvam@amd.com/
> Acked-by: Christian König <christian.koenig@amd.com>
> Reviewed-by: Matthew Auld <matthew.auld@intel.com>
> Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>

New unit test for this would be most excellent - these kind of missed edge
cases is exactly what kunit is for. Can you please follow up with, since
we don't want to hold up the bugfix for longer?
-Sima

> ---
>  drivers/gpu/drm/drm_buddy.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
> index f57e6d74fb0e..c1a99bf4dffd 100644
> --- a/drivers/gpu/drm/drm_buddy.c
> +++ b/drivers/gpu/drm/drm_buddy.c
> @@ -539,6 +539,12 @@ static int __alloc_range(struct drm_buddy *mm,
>  	} while (1);
>  
>  	list_splice_tail(&allocated, blocks);
> +
> +	if (total_allocated < size) {
> +		err = -ENOSPC;
> +		goto err_free;
> +	}
> +
>  	return 0;
>  
>  err_undo:
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch