Re: [PATCH v4 19/21] dma-buf: Document dynamic locking convention

[Christian König]

Am 31.08.22 um 17:37 schrieb Dmitry Osipenko:
> Add documentation for the dynamic locking convention. The documentation
> tells dma-buf API users when they should take the reservation lock and
> when not.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>

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

> ---
>   Documentation/driver-api/dma-buf.rst |  6 +++
>   drivers/dma-buf/dma-buf.c            | 64 ++++++++++++++++++++++++++++
>   2 files changed, 70 insertions(+)
>
> diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst
> index 36a76cbe9095..622b8156d212 100644
> --- a/Documentation/driver-api/dma-buf.rst
> +++ b/Documentation/driver-api/dma-buf.rst
> @@ -119,6 +119,12 @@ DMA Buffer ioctls
>   
>   .. kernel-doc:: include/uapi/linux/dma-buf.h
>   
> +DMA-BUF locking convention
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +.. kernel-doc:: drivers/dma-buf/dma-buf.c
> +   :doc: locking convention
> +
>   Kernel Functions and Structures Reference
>   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index d9130486cb8f..97ce884fad76 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -794,6 +794,70 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
>   	return sg_table;
>   }
>   
> +/**
> + * DOC: locking convention
> + *
> + * In order to avoid deadlock situations between dma-buf exports and importers,
> + * all dma-buf API users must follow the common dma-buf locking convention.
> + *
> + * Convention for importers
> + *
> + * 1. Importers must hold the dma-buf reservation lock when calling these
> + *    functions:
> + *
> + *     - dma_buf_pin()
> + *     - dma_buf_unpin()
> + *     - dma_buf_map_attachment()
> + *     - dma_buf_unmap_attachment()
> + *     - dma_buf_vmap()
> + *     - dma_buf_vunmap()
> + *
> + * 2. Importers must not hold the dma-buf reservation lock when calling these
> + *    functions:
> + *
> + *     - dma_buf_attach()
> + *     - dma_buf_dynamic_attach()
> + *     - dma_buf_detach()
> + *     - dma_buf_export(
> + *     - dma_buf_fd()
> + *     - dma_buf_get()
> + *     - dma_buf_put()
> + *     - dma_buf_mmap()
> + *     - dma_buf_begin_cpu_access()
> + *     - dma_buf_end_cpu_access()
> + *     - dma_buf_map_attachment_unlocked()
> + *     - dma_buf_unmap_attachment_unlocked()
> + *     - dma_buf_vmap_unlocked()
> + *     - dma_buf_vunmap_unlocked()
> + *
> + * Convention for exporters
> + *
> + * 1. These &dma_buf_ops callbacks are invoked with unlocked dma-buf
> + *    reservation and exporter can take the lock:
> + *
> + *     - &dma_buf_ops.attach()
> + *     - &dma_buf_ops.detach()
> + *     - &dma_buf_ops.release()
> + *     - &dma_buf_ops.begin_cpu_access()
> + *     - &dma_buf_ops.end_cpu_access()
> + *
> + * 2. These &dma_buf_ops callbacks are invoked with locked dma-buf
> + *    reservation and exporter can't take the lock:
> + *
> + *     - &dma_buf_ops.pin()
> + *     - &dma_buf_ops.unpin()
> + *     - &dma_buf_ops.map_dma_buf()
> + *     - &dma_buf_ops.unmap_dma_buf()
> + *     - &dma_buf_ops.mmap()
> + *     - &dma_buf_ops.vmap()
> + *     - &dma_buf_ops.vunmap()
> + *
> + * 3. Exporters must hold the dma-buf reservation lock when calling these
> + *    functions:
> + *
> + *     - dma_buf_move_notify()
> + */
> +
>   /**
>    * dma_buf_dynamic_attach - Add the device to dma_buf's attachments list
>    * @dmabuf:		[in]	buffer to attach device to.