Re: [PATCH 4/5] drm/tests: shmem: Hold reservation lock around madvise

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

On Fri, 12 Dec 2025 17:00:35 +0100
Thomas Zimmermann <tzimmermann@suse.de> wrote:

> Acquire and release the GEM object's reservation lock around calls
> to the object's madvide operation. The tests use
> drm_gem_shmem_madvise_locked(), which led to errors such as show below.
> 
> [   58.339389] WARNING: CPU: 1 PID: 1352 at drivers/gpu/drm/drm_gem_shmem_helper.c:499 drm_gem_shmem_madvise_locked+0xde/0x140
> 
> Only export the new helper drm_gem_shmem_madvise() 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 |  8 ++++----
>  include/drm/drm_gem_shmem_helper.h         |  1 +
>  3 files changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 06ef4e5adb7d..4ffcf6ed46f5 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -924,6 +924,21 @@ void drm_gem_shmem_vunmap(struct drm_gem_shmem_object *shmem, struct iosys_map *
>  	dma_resv_unlock(obj->resv);
>  }
>  EXPORT_SYMBOL_IF_KUNIT(drm_gem_shmem_vunmap);
> +
> +int drm_gem_shmem_madvise(struct drm_gem_shmem_object *shmem, int madv)
> +{
> +	struct drm_gem_object *obj = &shmem->base;
> +	int ret;
> +
> +	ret = dma_resv_lock_interruptible(obj->resv, NULL);
> +	if (ret)
> +		return ret;
> +	ret = drm_gem_shmem_madvise_locked(shmem, madv);
> +	dma_resv_unlock(obj->resv);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_IF_KUNIT(drm_gem_shmem_madvise);
>  #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 3e7c6f20fbcc..d639848e3c8e 100644
> --- a/drivers/gpu/drm/tests/drm_gem_shmem_test.c
> +++ b/drivers/gpu/drm/tests/drm_gem_shmem_test.c
> @@ -292,17 +292,17 @@ static void drm_gem_shmem_test_madvise(struct kunit *test)
>  	ret = kunit_add_action_or_reset(test, drm_gem_shmem_free_wrapper, shmem);
>  	KUNIT_ASSERT_EQ(test, ret, 0);
>  
> -	ret = drm_gem_shmem_madvise_locked(shmem, 1);
> +	ret = drm_gem_shmem_madvise(shmem, 1);
>  	KUNIT_EXPECT_TRUE(test, ret);
>  	KUNIT_ASSERT_EQ(test, shmem->madv, 1);
>  
>  	/* Set madv to a negative value */
> -	ret = drm_gem_shmem_madvise_locked(shmem, -1);
> +	ret = drm_gem_shmem_madvise(shmem, -1);
>  	KUNIT_EXPECT_FALSE(test, ret);
>  	KUNIT_ASSERT_EQ(test, shmem->madv, -1);
>  
>  	/* Check that madv cannot be set back to a positive value */
> -	ret = drm_gem_shmem_madvise_locked(shmem, 0);
> +	ret = drm_gem_shmem_madvise(shmem, 0);
>  	KUNIT_EXPECT_FALSE(test, ret);
>  	KUNIT_ASSERT_EQ(test, shmem->madv, -1);
>  }
> @@ -330,7 +330,7 @@ static void drm_gem_shmem_test_purge(struct kunit *test)
>  	ret = drm_gem_shmem_is_purgeable(shmem);
>  	KUNIT_EXPECT_FALSE(test, ret);
>  
> -	ret = drm_gem_shmem_madvise_locked(shmem, 1);
> +	ret = drm_gem_shmem_madvise(shmem, 1);
>  	KUNIT_EXPECT_TRUE(test, ret);
>  
>  	/* The scatter/gather table will be freed by drm_gem_shmem_free */
> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> index 6924ee226655..3dd93e2df709 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -310,6 +310,7 @@ struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
>  #if IS_ENABLED(CONFIG_KUNIT)
>  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);
>  #endif
>  
>  #endif /* __DRM_GEM_SHMEM_HELPER_H__ */