[PATCH] drm/virtio: exbuf->fence_fd unmodified on interrupted wait

[Dmitry Osipenko]

On 1/27/23 01:58, Ryan Neph wrote:
> An interrupted dma_fence_wait() becomes an -ERESTARTSYS returned
> to userspace ioctl(DRM_IOCTL_VIRTGPU_EXECBUFFER) calls, prompting to
> retry the ioctl(), but the passed exbuf->fence_fd has been reset to -1,
> making the retry attempt fail at sync_file_get_fence().
> 
> The uapi for DRM_IOCTL_VIRTGPU_EXECBUFFER is changed to retain the
> passed value for exbuf->fence_fd when returning ERESTARTSYS or EINTR.
> 
> Fixes: 2cd7b6f08bc4 ("drm/virtio: add in/out fence support for explicit synchronization")
> Signed-off-by: Ryan Neph <ryanneph at chromium.org>
> ---
> 
>  drivers/gpu/drm/virtio/virtgpu_ioctl.c | 9 ++++++---
>  include/uapi/drm/virtgpu_drm.h         | 3 +++
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> index 9f4a90493aea..ffce4e2a409a 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> @@ -132,6 +132,8 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
>  	uint64_t fence_ctx;
>  	uint32_t ring_idx;
>  
> +	exbuf->fence_fd = -1;
> +
>  	fence_ctx = vgdev->fence_drv.context;
>  	ring_idx = 0;
>  
> @@ -152,8 +154,6 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
>  		ring_idx = exbuf->ring_idx;
>  	}
>  
> -	exbuf->fence_fd = -1;

Is there any userspace relying on this -1 behaviour? Wouldn't be better
to remove this offending assignment?

-- 
Best regards,
Dmitry