linux-kernel - Re: [PATCH] drm/i915: Fix comparison bug

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Date:	Tue, 29 Sep 2015 10:37:30 +0300
From:	Jani Nikula <jani.nikula@...ux.intel.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Daniel Vetter <daniel.vetter@...el.com>,
	David Airlie <airlied@...ux.ie>
Cc:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/i915: Fix comparison bug

On Tue, 29 Sep 2015, Rasmus Villemoes <linux@...musvillemoes.dk> wrote:
> ->stolen->start has type u64 aka unsigned long long; relying on the
> difference (effectively cast to int) for sorting is wrong.
>
> It wouldn't be a problem in practice if the values compared are always
> within INT_MAX of each other (so that the difference is actually
> representable in an int), but 440fd5283a87 ("drm/mm: Support 4 GiB and
> larger ranges") strongly suggests that's not the case.
>
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>

Reviewed-by: Jani Nikula <jani.nikula@...el.com>


> ---
>  drivers/gpu/drm/i915/i915_debugfs.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index e3ec9049081f..5207e681a987 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -258,7 +258,11 @@ static int obj_rank_by_stolen(void *priv,
>  	struct drm_i915_gem_object *b =
>  		container_of(B, struct drm_i915_gem_object, obj_exec_link);
>  
> -	return a->stolen->start - b->stolen->start;
> +	if (a->stolen->start < b->stolen->start)
> +		return -1;
> +	if (a->stolen->start > b->stolen->start)
> +		return 1;
> +	return 0;
>  }
>  
>  static int i915_gem_stolen_list_info(struct seq_file *m, void *data)
> -- 
> 2.1.3
>

-- 
Jani Nikula, Intel Open Source Technology Center
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