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

[Rob Clark]

On Fri, Jan 27, 2023 at 12:31 AM Ryan Neph <ryanneph at chromium.org> 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>

Reviewed-by: Rob Clark <robdclark at gmail.com>

> ---
>
>  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;
> -
>         virtio_gpu_create_context(dev, file);
>         if (exbuf->flags & VIRTGPU_EXECBUF_FENCE_FD_IN) {
>                 struct dma_fence *in_fence;
> @@ -173,7 +173,7 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
>
>                 dma_fence_put(in_fence);
>                 if (ret)
> -                       return ret;
> +                       goto out_err;
>         }
>
>         if (exbuf->flags & VIRTGPU_EXECBUF_FENCE_FD_OUT) {
> @@ -259,6 +259,9 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
>
>         if (out_fence_fd >= 0)
>                 put_unused_fd(out_fence_fd);
> +out_err:
> +       if (ret == -EINTR || ret == -ERESTARTSYS)
> +               exbuf->fence_fd = in_fence_fd;
>
>         return ret;
>  }
> diff --git a/include/uapi/drm/virtgpu_drm.h b/include/uapi/drm/virtgpu_drm.h
> index 0512fde5e697..ac8d1eed12ab 100644
> --- a/include/uapi/drm/virtgpu_drm.h
> +++ b/include/uapi/drm/virtgpu_drm.h
> @@ -64,6 +64,9 @@ struct drm_virtgpu_map {
>         __u32 pad;
>  };
>
> +/* For ioctl() returning ERESTARTSYS or EINTR, fence_fd is unmodified.
> + * For all other errors it is set to -1.
> + */
>  struct drm_virtgpu_execbuffer {
>         __u32 flags;
>         __u32 size;
> --
> 2.39.1.456.gfc5497dd1b-goog
>