Re: [PATCH v3 9/9] dma-buf: Remove internal lock

["Christian König" <christian.koenig@amd.com>]

Am 24.08.22 um 12:22 schrieb Dmitry Osipenko:
> The internal dma-buf lock isn't needed anymore because the updated
> locking specification claims that dma-buf reservation must be locked
> by importers, and thus, the internal data is already protected by the
> reservation lock. Remove the obsoleted internal lock.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

Reviewed-by: Christian König <christian.koenig@amd.com>

> ---
>   drivers/dma-buf/dma-buf.c | 14 ++++----------
>   include/linux/dma-buf.h   |  9 ---------
>   2 files changed, 4 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 696d132b02f4..a0406254f0ae 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -656,7 +656,6 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
>   
>   	dmabuf->file = file;
>   
> -	mutex_init(&dmabuf->lock);
>   	INIT_LIST_HEAD(&dmabuf->attachments);
>   
>   	mutex_lock(&db_list.lock);
> @@ -1503,7 +1502,7 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_mmap_unlocked, DMA_BUF);
>   int dma_buf_vmap(struct dma_buf *dmabuf, struct iosys_map *map)
>   {
>   	struct iosys_map ptr;
> -	int ret = 0;
> +	int ret;
>   
>   	iosys_map_clear(map);
>   
> @@ -1515,28 +1514,25 @@ int dma_buf_vmap(struct dma_buf *dmabuf, struct iosys_map *map)
>   	if (!dmabuf->ops->vmap)
>   		return -EINVAL;
>   
> -	mutex_lock(&dmabuf->lock);
>   	if (dmabuf->vmapping_counter) {
>   		dmabuf->vmapping_counter++;
>   		BUG_ON(iosys_map_is_null(&dmabuf->vmap_ptr));
>   		*map = dmabuf->vmap_ptr;
> -		goto out_unlock;
> +		return 0;
>   	}
>   
>   	BUG_ON(iosys_map_is_set(&dmabuf->vmap_ptr));
>   
>   	ret = dmabuf->ops->vmap(dmabuf, &ptr);
>   	if (WARN_ON_ONCE(ret))
> -		goto out_unlock;
> +		return ret;
>   
>   	dmabuf->vmap_ptr = ptr;
>   	dmabuf->vmapping_counter = 1;
>   
>   	*map = dmabuf->vmap_ptr;
>   
> -out_unlock:
> -	mutex_unlock(&dmabuf->lock);
> -	return ret;
> +	return 0;
>   }
>   EXPORT_SYMBOL_NS_GPL(dma_buf_vmap, DMA_BUF);
>   
> @@ -1578,13 +1574,11 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, struct iosys_map *map)
>   	BUG_ON(dmabuf->vmapping_counter == 0);
>   	BUG_ON(!iosys_map_is_equal(&dmabuf->vmap_ptr, map));
>   
> -	mutex_lock(&dmabuf->lock);
>   	if (--dmabuf->vmapping_counter == 0) {
>   		if (dmabuf->ops->vunmap)
>   			dmabuf->ops->vunmap(dmabuf, map);
>   		iosys_map_clear(&dmabuf->vmap_ptr);
>   	}
> -	mutex_unlock(&dmabuf->lock);
>   }
>   EXPORT_SYMBOL_NS_GPL(dma_buf_vunmap, DMA_BUF);
>   
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index d48d534dc55c..aed6695bbb50 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -326,15 +326,6 @@ struct dma_buf {
>   	/** @ops: dma_buf_ops associated with this buffer object. */
>   	const struct dma_buf_ops *ops;
>   
> -	/**
> -	 * @lock:
> -	 *
> -	 * Used internally to serialize list manipulation, attach/detach and
> -	 * vmap/unmap. Note that in many cases this is superseeded by
> -	 * dma_resv_lock() on @resv.
> -	 */
> -	struct mutex lock;
> -
>   	/**
>   	 * @vmapping_counter:
>   	 *