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 --- Documentation/driver-api/dma-buf.rst | 6 +++ drivers/dma-buf/dma-buf.c | 63 ++++++++++++++++++++++++++++ 2 files changed, 69 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 f2a5a122da4a..696d132b02f4 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -794,6 +794,69 @@ 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_unlocked() + * - dma_buf_dynamic_attach_unlocked() + * - dma_buf_detach_unlocked() + * - dma_buf_export( + * - dma_buf_fd() + * - dma_buf_get() + * - dma_buf_put() + * - 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_unlocked - Add the device to dma_buf's attachments list * @dmabuf: [in] buffer to attach device to.