linux-kernel - Re: [PATCH] Use drm_gem_shmem_unpin() to unpin the backing pages for a shmem GEM

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Message-ID: <20250827100748.0d7fb9d1@fedora>
Date: Wed, 27 Aug 2025 10:07:48 +0200
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Xiaolei Wang <xiaolei.wang@...driver.com>
Cc: maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
 tzimmermann@...e.de, dmitry.baryshkov@....qualcomm.com, airlied@...il.com,
 simona@...ll.ch, dmitry.osipenko@...labora.com,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Use drm_gem_shmem_unpin() to unpin the backing pages
 for a shmem GEM

On Wed, 27 Aug 2025 10:25:16 +0800
Xiaolei Wang <xiaolei.wang@...driver.com> wrote:

> Although drm_gem_shmem_free() will decrease the use count
> on the backing pages and free backing pages for a GEM object,
> the pages_pin_count count is not decremented, which results
> in a warning. Therefore, use drm_gem_shmem_unpin() to unpin
> the backing pages for a shmem GEM.

With the subject prefixed with "drm/gem-shmem: " this is

Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>

> 
> WARNING: CPU: 2 PID: 1106 at drivers/gpu/drm/drm_gem_shmem_helper.c:180 drm_gem_shmem_free+0x4d0/0x6f0
>  Call trace:
>   drm_gem_shmem_free+0x4d0/0x6f0 (P)
>   drm_gem_shmem_free_wrapper+0x10/0x1c
>   __kunit_action_free+0x50/0x70
>   kunit_remove_resource+0x144/0x1e4
>   kunit_cleanup+0x64/0xfc
>   kunit_try_run_case_cleanup+0xa0/0xd4
>   kunit_generic_run_threadfn_adapter+0x80/0xec
>   kthread+0x3b8/0x6c0
>   ret_from_fork+0x10/0x20
> 
> Fixes: 93032ae634d4 ("drm/test: add a test suite for GEM objects backed by shmem")
> Signed-off-by: Xiaolei Wang <xiaolei.wang@...driver.com>
> ---
>  drivers/gpu/drm/tests/drm_gem_shmem_test.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/tests/drm_gem_shmem_test.c b/drivers/gpu/drm/tests/drm_gem_shmem_test.c
> index 68f2c3162354..e0a9f3a917ed 100644
> --- a/drivers/gpu/drm/tests/drm_gem_shmem_test.c
> +++ b/drivers/gpu/drm/tests/drm_gem_shmem_test.c
> @@ -227,6 +227,7 @@ static void drm_gem_shmem_test_get_pages_sgt(struct kunit *test)
>  		len += sg->length;
>  	}
>  
> +	drm_gem_shmem_unpin(shmem);
>  	KUNIT_EXPECT_GE(test, len, TEST_SIZE);
>  }
>