From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx> >From the description of the "DMA-BUF/GEM Object references and lifetime overview" it is not clear when exactly dma_buf gets destroyed and memory freed: only driver .release function mentioned which makes confusion on the real buffer's lifetime. Add more description so all the paths are covered. Cc: Rob Clark <robdclark@xxxxxxxxx> Cc: Dave Airlie <airlied@xxxxxxxx> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx> --- drivers/gpu/drm/drm_prime.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c index 8d77b2462594..c061a0b29819 100644 --- a/drivers/gpu/drm/drm_prime.c +++ b/drivers/gpu/drm/drm_prime.c @@ -41,7 +41,7 @@ * object. It takes this reference in handle_to_fd_ioctl, when it * first calls .prime_export and stores the exporting GEM object in * the dma_buf priv. This reference is released when the dma_buf - * object goes away in the driver .release function. + * object goes away. * * On the import the importing GEM object holds a reference to the * dma_buf (which in turn holds a ref to the exporting GEM object). @@ -51,6 +51,13 @@ * when the imported object is destroyed, we remove the attachment * and drop the reference to the dma_buf. * + * When all the references to the dma_buf are dropped, e.g. when + * userspace closes both handles to the imported (fd_to_handle_ioctl) + * and exported (handle_to_fd_ioctl) dma_buf and closes the corresponding + * file descriptor (handle_to_fd), then dma_buf gets destroyed. + * This can also happen as a part of the clean up procedure in the + * driver .release function if userspace fails to properly clean up. + * * Thus the chain of references always flows in one direction * (avoiding loops): importing_gem -> dmabuf -> exporting_gem * -- 2.7.4 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
