linux-kernel - Re: [PATCH v17 11/18] drm/shmem-helper: Improve drm_gem_shmem_vmap

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Date:   Fri, 15 Sep 2023 09:18:18 +0200
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 v17 11/18] drm/shmem-helper: Improve
 drm_gem_shmem_vmap_locked() error handling

On Fri, 15 Sep 2023 02:27:14 +0300
Dmitry Osipenko <dmitry.osipenko@...labora.com> wrote:

> Remove error unwinding from drm_gem_shmem_vmap_locked() making error
> paths consistent for both dmabuf and non-dmabuf cases and improving
> readability of the code. Often it's preferred to do the explicit error
> unwinding, but this multi-path function is an exception.
> 
> Suggested-by: Boris Brezillon <boris.brezillon@...labora.com>

Actually, I suggested returning directly, but I hadn't noticed the debug
message which you pointed in one of your replies. No longer sure it's a
good idea to drop the error path, since it makes code addition more
error-prone (pretty easy to forget the drm_gem_shmem_unpin_locked() in
new error paths).

> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 13 +++----------
>  1 file changed, 3 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index e1fcb5154209..8a8eab4d0332 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -334,7 +334,7 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
>  			      struct iosys_map *map)
>  {
>  	struct drm_gem_object *obj = &shmem->base;
> -	int ret = 0;
> +	int ret;
>  
>  	if (obj->import_attach) {
>  		ret = dma_buf_vmap(obj->import_attach->dmabuf, map);
> @@ -357,6 +357,7 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
>  		shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
>  				    VM_MAP, prot);
>  		if (!shmem->vaddr) {
> +			drm_gem_shmem_unpin_locked(shmem);
>  			ret = -ENOMEM;
>  		} else {
>  			iosys_map_set_vaddr(map, shmem->vaddr);
> @@ -364,16 +365,8 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
>  		}
>  	}
>  
> -	if (ret) {
> +	if (ret)
>  		drm_dbg_kms(obj->dev, "Failed to vmap pages, error %d\n", ret);
> -		goto err_put_pages;
> -	}
> -
> -	return 0;
> -
> -err_put_pages:
> -	if (!obj->import_attach)
> -		drm_gem_shmem_unpin_locked(shmem);
>  
>  	return ret;
>  }