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SubjectRe: [PATCH v4 19/21] dma-buf: Document dynamic locking convention
From
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@collabora.com>

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

> ---
> 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.

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