diff options
Diffstat (limited to 'drivers/gpu/drm/drm_prime.c')
| -rw-r--r-- | drivers/gpu/drm/drm_prime.c | 19 |
1 files changed, 16 insertions, 3 deletions
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c index 8d77b2462594..25aa4558f1b5 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 reference needs to be released when the + * 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 +54,16 @@ * 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, i.e. when + * userspace has closed both handles to the imported GEM object (through the + * FD_TO_HANDLE IOCTL) and closed the file descriptor of the exported + * (through the HANDLE_TO_FD IOCTL) dma_buf, and all kernel-internal references + * are also gone, then the dma_buf gets destroyed. This can also happen as a + * part of the clean up procedure in the drm_release() function if userspace + * fails to properly clean up. 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 * @@ -291,7 +304,7 @@ static void drm_gem_unmap_dma_buf(struct dma_buf_attachment *attach, * This wraps dma_buf_export() for use by generic GEM drivers that are using * drm_gem_dmabuf_release(). In addition to calling dma_buf_export(), we take * a reference to the &drm_device and the exported &drm_gem_object (stored in - * exp_info->priv) which is released by drm_gem_dmabuf_release(). + * &dma_buf_export_info.priv) which is released by drm_gem_dmabuf_release(). * * Returns the new dmabuf. */ |