linux-kernel - Re: [PATCH v18 11/26] drm/shmem-helper: Prepare drm_gem_shmem

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Date:   Fri, 10 Nov 2023 11:16:01 +0100
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     David Airlie <airlied@...il.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Christian König <christian.koenig@....com>,
        Qiang Yu <yuq825@...il.com>,
        Steven Price <steven.price@....com>,
        Emma Anholt <emma@...olt.net>, Melissa Wen <mwen@...lia.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v18 11/26] drm/shmem-helper: Prepare
 drm_gem_shmem_free() to shrinker addition

On Mon, 30 Oct 2023 02:01:50 +0300
Dmitry Osipenko <dmitry.osipenko@...labora.com> wrote:

> Prepare drm_gem_shmem_free() to addition of memory shrinker support
> to drm-shmem by adding and using variant of put_pages() that doesn't
> touch reservation lock. Reservation shouldn't be touched because lockdep
> will trigger a bogus warning about locking contention with fs_reclaim
> code paths that can't happen during the time when GEM is freed and
> lockdep doesn't know about that.
> 
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 35 +++++++++++++-------------
>  1 file changed, 18 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 08b5a57c59d8..24ff2b99e75b 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -128,6 +128,22 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t
>  }
>  EXPORT_SYMBOL_GPL(drm_gem_shmem_create);
>  
> +static void
> +drm_gem_shmem_free_pages(struct drm_gem_shmem_object *shmem)
> +{
> +	struct drm_gem_object *obj = &shmem->base;
> +
> +#ifdef CONFIG_X86
> +	if (shmem->map_wc)
> +		set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
> +#endif
> +
> +	drm_gem_put_pages(obj, shmem->pages,
> +			  shmem->pages_mark_dirty_on_put,
> +			  shmem->pages_mark_accessed_on_put);
> +	shmem->pages = NULL;
> +}
> +
>  /**
>   * drm_gem_shmem_free - Free resources associated with a shmem GEM object
>   * @shmem: shmem GEM object to free
> @@ -142,8 +158,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
>  	if (obj->import_attach) {
>  		drm_prime_gem_destroy(obj, shmem->sgt);
>  	} else {
> -		dma_resv_lock(shmem->base.resv, NULL);
> -
>  		drm_WARN_ON(obj->dev, refcount_read(&shmem->vmap_use_count));
>  
>  		if (shmem->sgt) {
> @@ -157,8 +171,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
>  

If you drop the dma_resv_lock/unlock(), you should also replace the
drm_gem_shmem_put_pages_locked() by a drm_gem_shmem_free_pages() in this
commit.

>  		drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_use_count));
>  		drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_pin_count));
> -
> -		dma_resv_unlock(shmem->base.resv);
>  	}
>  
>  	drm_gem_object_release(obj);
> @@ -208,21 +220,10 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
>   */
>  void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
>  {
> -	struct drm_gem_object *obj = &shmem->base;
> -
>  	dma_resv_assert_held(shmem->base.resv);
>  
> -	if (refcount_dec_and_test(&shmem->pages_use_count)) {
> -#ifdef CONFIG_X86
> -		if (shmem->map_wc)
> -			set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
> -#endif
> -
> -		drm_gem_put_pages(obj, shmem->pages,
> -				  shmem->pages_mark_dirty_on_put,
> -				  shmem->pages_mark_accessed_on_put);
> -		shmem->pages = NULL;
> -	}
> +	if (refcount_dec_and_test(&shmem->pages_use_count))
> +		drm_gem_shmem_free_pages(shmem);
>  }
>  EXPORT_SYMBOL_GPL(drm_gem_shmem_put_pages_locked);
>