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

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Date: Fri, 16 Feb 2024 17:31:03 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Arnd Bergmann <arnd@...nel.org>,
 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: Re: [PATCH] drm/tests/drm_buddy: avoid 64-bit calculation



On 2/16/24 12:24, Arnd Bergmann wrote:
> 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>

Tested-by: Randy Dunlap <rdunlap@...radead.org>

Thanks.

> ---
>  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;

-- 
#Randy