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

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Message-Id: <1443474531-11560-1-git-send-email-linux@rasmusvillemoes.dk>
Date:	Mon, 28 Sep 2015 23:08:50 +0200
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Daniel Vetter <daniel.vetter@...el.com>,
	Jani Nikula <jani.nikula@...ux.intel.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: [PATCH] drm/i915: Fix comparison bug

->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>
---
 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

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