On Fri, Jan 27, 2017 at 09:04:25AM +0200, Oleksandr Andrushchenko wrote: > 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 | 16 ++++++++++++++-- > 1 file changed, 14 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c > index 8d77b2462594..893a1a6311f0 100644 > --- a/drivers/gpu/drm/drm_prime.c > +++ b/drivers/gpu/drm/drm_prime.c > @@ -40,8 +40,11 @@ > * On the export the dma_buf holds a reference to the exporting GEM > * 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. > + * the dma_buf priv. This refernce needs to be released when the s/refernce/reference/ > + * final reference to the &dma_buf itself is dropped and its > + * &dma_buf_ops.release function is called. For GEM-based drivers, > + * the dma_buf should be exported using drm_gem_dmabuf_export() and > + * then released by drm_gem_dmabuf_release(). > * > * 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 +54,15 @@ > * 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 Usualla we call ioctls with uppercase, e.g. HANDLE_TO_FD IOCTL. > + * 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. Extended the references here to full file_ops one. Since this is all tiny, I've done this while applying, thanks a lot for your patch. -Daniel > + * Note that both the kernel and userspace (by keeeping the PRIME file > + * descriptors open) can hold references onto a &dma_buf. > + * > * Thus the chain of references always flows in one direction > * (avoiding loops): importing_gem -> dmabuf -> exporting_gem > * > -- > 2.7.4 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
