[PATCH] drm/i915: Fix comparison bug

[PATCH] drm/i915: Fix comparison bug

[Rasmus Villemoes]

->stolen->start has type unsigned long; relying on the difference
(effectively cast to int) for sorting is wrong.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
 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 063b44817e08..adfb863bb580 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -236,7 +236,11 @@ 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

Re: [PATCH] drm/i915: Fix comparison bug

[Jani Nikula]

On Tue, 29 Sep 2015, Rasmus Villemoes <linux@rasmusvillemoes.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@rasmusvillemoes.dk>

Reviewed-by: Jani Nikula <jani.nikula@intel.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

[PATCH] drm/i915: Fix comparison bug

[Rasmus Villemoes]

->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@rasmusvillemoes.dk>
---
 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