Re: [PATCH 5/5] drm/tests: shmem: Hold reservation lock around purge

[Boris Brezillon <boris.brezillon@collabora.com>]

On Fri, 12 Dec 2025 17:00:36 +0100
Thomas Zimmermann <tzimmermann@suse.de> wrote:

> Acquire and release the GEM object's reservation lock around calls
> to the object's purge operation. The tests use
> drm_gem_shmem_purge_locked(), which led to errors such as show below.
> 
> [   58.709128] WARNING: CPU: 1 PID: 1354 at drivers/gpu/drm/drm_gem_shmem_helper.c:515 drm_gem_shmem_purge_locked+0x51c/0x740
> 
> Only export the new helper drm_gem_shmem_purge() for Kunit tests.
> This is not an interface for regular drivers.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Fixes: 954907f7147d ("drm/shmem-helper: Refactor locked/unlocked functions")
> Cc: dri-devel@lists.freedesktop.org
> Cc: <stable@vger.kernel.org> # v6.16+

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

> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c     | 15 +++++++++++++++
>  drivers/gpu/drm/tests/drm_gem_shmem_test.c |  4 +++-
>  include/drm/drm_gem_shmem_helper.h         |  1 +
>  3 files changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 4ffcf6ed46f5..dfc24392cb61 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -939,6 +939,21 @@ int drm_gem_shmem_madvise(struct drm_gem_shmem_object *shmem, int madv)
>  	return ret;
>  }
>  EXPORT_SYMBOL_IF_KUNIT(drm_gem_shmem_madvise);
> +
> +int drm_gem_shmem_purge(struct drm_gem_shmem_object *shmem)
> +{
> +	struct drm_gem_object *obj = &shmem->base;
> +	int ret;
> +
> +	ret = dma_resv_lock_interruptible(obj->resv, NULL);
> +	if (ret)
> +		return ret;
> +	drm_gem_shmem_purge_locked(shmem);
> +	dma_resv_unlock(obj->resv);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_IF_KUNIT(drm_gem_shmem_purge);
>  #endif
>  
>  MODULE_DESCRIPTION("DRM SHMEM memory-management helpers");
> diff --git a/drivers/gpu/drm/tests/drm_gem_shmem_test.c b/drivers/gpu/drm/tests/drm_gem_shmem_test.c
> index d639848e3c8e..4b459f21acfd 100644
> --- a/drivers/gpu/drm/tests/drm_gem_shmem_test.c
> +++ b/drivers/gpu/drm/tests/drm_gem_shmem_test.c
> @@ -340,7 +340,9 @@ static void drm_gem_shmem_test_purge(struct kunit *test)
>  	ret = drm_gem_shmem_is_purgeable(shmem);
>  	KUNIT_EXPECT_TRUE(test, ret);
>  
> -	drm_gem_shmem_purge_locked(shmem);
> +	ret = drm_gem_shmem_purge(shmem);
> +	KUNIT_ASSERT_EQ(test, ret, 0);
> +
>  	KUNIT_EXPECT_NULL(test, shmem->pages);
>  	KUNIT_EXPECT_NULL(test, shmem->sgt);
>  	KUNIT_EXPECT_EQ(test, shmem->madv, -1);
> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> index 3dd93e2df709..8d56970d7eed 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -311,6 +311,7 @@ struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
>  int drm_gem_shmem_vmap(struct drm_gem_shmem_object *shmem, struct iosys_map *map);
>  void drm_gem_shmem_vunmap(struct drm_gem_shmem_object *shmem, struct iosys_map *map);
>  int drm_gem_shmem_madvise(struct drm_gem_shmem_object *shmem, int madv);
> +int drm_gem_shmem_purge(struct drm_gem_shmem_object *shmem);
>  #endif
>  
>  #endif /* __DRM_GEM_SHMEM_HELPER_H__ */