Use drm_gem_shmem_unpin() to unpin the backing pages for a shmem GEM

[PATCH] Use drm_gem_shmem_unpin() to unpin the backing pages for a shmem GEM

Posted by Xiaolei Wang 1 month, 1 week ago

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.

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@windriver.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);
 }
 
-- 
2.43.0

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

Posted by Boris Brezillon 1 month, 1 week ago

On Wed, 27 Aug 2025 10:25:16 +0800
Xiaolei Wang <xiaolei.wang@windriver.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@collabora.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@windriver.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);
>  }
>