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

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Date: Mon, 19 Feb 2024 12:22:28 +0100
From: Christian König <christian.koenig@....com>
To: Randy Dunlap <rdunlap@...radead.org>, 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>,
 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

Am 17.02.24 um 02:31 schrieb Randy Dunlap:
> 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>

I've just pushed a similar patch Mathew came up a bit earlier to 
drm-misc-fixes.

Sorry for the noise, I have to catch up on picking up patches for 
misc-fixes and misc-next.

Christian.

>
> 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;