linux-kernel - [PATCH] drm/tests/drm_buddy: avoid 64-bit calculation

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Date: Fri, 16 Feb 2024 21:24:30 +0100
From: Arnd Bergmann <arnd@...nel.org>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>
Cc: Arnd Bergmann <arnd@...db.de>,
	David Airlie <airlied@...il.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@....com>,
	Christian König <christian.koenig@....com>,
	David Gow <davidgow@...gle.com>,
	Maíra Canal <mcanal@...lia.com>,
	Matthew Auld <matthew.auld@...el.com>,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] drm/tests/drm_buddy: avoid 64-bit calculation

From: Arnd Bergmann <arnd@...db.de>

The newly added drm_test_buddy_alloc_contiguous() test fails to link on
32-bit targets because of inadvertent 64-bit calculations:

ERROR: modpost: "__aeabi_uldivmod" [drivers/gpu/drm/tests/drm_buddy_test.ko] undefined!
ERROR: modpost: "__aeabi_ldivmod" [drivers/gpu/drm/tests/drm_buddy_test.ko] undefined!

>From what I can tell, the numbers cannot possibly overflow a 32-bit size,
so use different types for these.

I noticed that the function has another possible flaw in that is mixes
what it calls pages with 4KB units. This is a big confusing at best,
or possibly broken when built on machines with larger pages.

Fixes: a64056bb5a32 ("drm/tests/drm_buddy: add alloc_contiguous test")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/gpu/drm/tests/drm_buddy_test.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/tests/drm_buddy_test.c b/drivers/gpu/drm/tests/drm_buddy_test.c
index fee6bec757d1..50a5f98cd5bd 100644
--- a/drivers/gpu/drm/tests/drm_buddy_test.c
+++ b/drivers/gpu/drm/tests/drm_buddy_test.c
@@ -21,7 +21,8 @@ static inline u64 get_size(int order, u64 chunk_size)
 
 static void drm_test_buddy_alloc_contiguous(struct kunit *test)
 {
-	u64 mm_size, ps = SZ_4K, i, n_pages, total;
+	u64 mm_size, total;
+	u32 i, ps = SZ_4K, n_pages;
 	struct drm_buddy_block *block;
 	struct drm_buddy mm;
 	LIST_HEAD(left);
@@ -29,7 +30,8 @@ static void drm_test_buddy_alloc_contiguous(struct kunit *test)
 	LIST_HEAD(right);
 	LIST_HEAD(allocated);
 
-	mm_size = 16 * 3 * SZ_4K;
+	n_pages = 16 * 3;
+	mm_size = n_pages * SZ_4K;
 
 	KUNIT_EXPECT_FALSE(test, drm_buddy_init(&mm, mm_size, ps));
 
@@ -42,7 +44,6 @@ static void drm_test_buddy_alloc_contiguous(struct kunit *test)
 	 */
 
 	i = 0;
-	n_pages = mm_size / ps;
 	do {
 		struct list_head *list;
 		int slot = i % 3;
-- 
2.39.2