Re: [PATCH v2] drm/tests/gpu_buddy: fix interleaving in buffer clearance test

On 03/08/2026 07:56, Arunpravin Paneer Selvam wrote:
> The resume clearance test skipped every other allocation, expecting an
> interleaved clear/dirty layout. But the buddy allocator hands out blocks
> contiguously, so this just allocated half the pages in one chunk and never
> exercised gpu_buddy_reset_clear()'s force-merge of opposite-state buddies.
> Allocate all pages into two lists instead and free one cleared, one dirty,
> to build a truly interleaved pattern.
> 
> v2: Use for loops instead of do-while for the allocation loops (Jani Nikula)
> 
> Fixes: e3335ccbf4da ("drm/tests/gpu_buddy: add a new test case for buffer clearance during resume")
> Reported-by: Sashiko-bot <[email protected]>
> Closes: https://sashiko.dev/#/patchset/[email protected]?part=1
> Cc: Matthew Auld <[email protected]>
> Cc: Christian König <[email protected]>
> Assisted-by: GitHub_Copilot:claude-opus-4.8
> Signed-off-by: Arunpravin Paneer Selvam <[email protected]>

Reviewed-by: Matthew Auld <[email protected]>

> ---
>   drivers/gpu/tests/gpu_buddy_test.c | 57 +++++++++++++++++-------------
>   1 file changed, 33 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/gpu/tests/gpu_buddy_test.c b/drivers/gpu/tests/gpu_buddy_test.c
> index 89698563c61b..e258bf1fa0fb 100644
> --- a/drivers/gpu/tests/gpu_buddy_test.c
> +++ b/drivers/gpu/tests/gpu_buddy_test.c
> @@ -1004,42 +1004,51 @@ static void gpu_test_buddy_alloc_clear(struct kunit *test)
>   	gpu_buddy_fini(&mm);
>   
>   	/*
> -	 * Using a non-power-of-two mm size, allocate alternating blocks of 4KiB in an
> -	 * even sequence and free them as cleared. All blocks should be marked as
> -	 * dirty and the split blocks should be merged back to their original
> -	 * size when the blocks clear reset function is called.
> +	 * Using a non-power-of-two mm size, allocate all 4KiB blocks and split
> +	 * them across two alternating lists, then free one list as cleared and
> +	 * the other as dirty. This interleaves cleared and dirty blocks so that
> +	 * neighbouring buddies cannot be merged, fragmenting the address space.
> +	 * After gpu_buddy_reset_clear(false) every block should be marked dirty
> +	 * and the split blocks should be merged back to their original size, so
> +	 * clear_avail must drop to 0.
>   	 */
>   	KUNIT_EXPECT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
>   	KUNIT_EXPECT_EQ(test, mm.max_order, max_order);
>   
> -	i = 0;
>   	n_pages = mm_size / ps;
> -	do {
> -		if (i % 2 == 0)
> -			KUNIT_ASSERT_FALSE_MSG(test, gpu_buddy_alloc_blocks(&mm, 0, mm_size,
> -									    ps, ps, &allocated, 0),
> -					"buddy_alloc hit an error size=%lu\n", ps);
> -	} while (++i < n_pages);
> +	for (i = 0; i < n_pages; i++) {
> +		struct list_head *list = (i % 2) ? &clean : &dirty;
>   
> -	gpu_buddy_free_list(&mm, &allocated, GPU_BUDDY_CLEARED);
> +		KUNIT_ASSERT_FALSE_MSG(test, gpu_buddy_alloc_blocks(&mm, 0, mm_size,
> +								    ps, ps, list, 0),
> +				"buddy_alloc hit an error size=%lu\n", ps);
> +	}
> +
> +	gpu_buddy_free_list(&mm, &clean, GPU_BUDDY_CLEARED);
> +	gpu_buddy_free_list(&mm, &dirty, 0);
>   	gpu_buddy_reset_clear(&mm, false);
>   	KUNIT_EXPECT_EQ(test, mm.clear_avail, 0);
> +	gpu_buddy_fini(&mm);
>   
>   	/*
> -	 * Using a non-power-of-two mm size, allocate alternating blocks of 4KiB in an
> -	 * odd sequence and free them as cleared. All blocks should be marked as
> -	 * cleared and the split blocks should be merged back to their original
> -	 * size when the blocks clear reset function is called.
> +	 * Repeat the same fragmented setup, but this time call
> +	 * gpu_buddy_reset_clear(true). Every block should be marked cleared and
> +	 * the split blocks should be merged back to their original size, so the
> +	 * whole address space (clear_avail) must equal mm_size.
>   	 */
> -	i = 0;
> -	do {
> -		if (i % 2 != 0)
> -			KUNIT_ASSERT_FALSE_MSG(test, gpu_buddy_alloc_blocks(&mm, 0, mm_size,
> -									    ps, ps, &allocated, 0),
> -					"buddy_alloc hit an error size=%lu\n", ps);
> -	} while (++i < n_pages);
> +	KUNIT_EXPECT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
> +	KUNIT_EXPECT_EQ(test, mm.max_order, max_order);
>   
> -	gpu_buddy_free_list(&mm, &allocated, GPU_BUDDY_CLEARED);
> +	for (i = 0; i < n_pages; i++) {
> +		struct list_head *list = (i % 2) ? &clean : &dirty;
> +
> +		KUNIT_ASSERT_FALSE_MSG(test, gpu_buddy_alloc_blocks(&mm, 0, mm_size,
> +								    ps, ps, list, 0),
> +				"buddy_alloc hit an error size=%lu\n", ps);
> +	}
> +
> +	gpu_buddy_free_list(&mm, &clean, GPU_BUDDY_CLEARED);
> +	gpu_buddy_free_list(&mm, &dirty, 0);
>   	gpu_buddy_reset_clear(&mm, true);
>   	KUNIT_EXPECT_EQ(test, mm.clear_avail, mm_size);
>   	gpu_buddy_fini(&mm);
> 
> base-commit: bc47d5937f21c5fc94504f03e18f1adb56d97634