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    SubjectRe: [PATCH] drm/virtio: exbuf->fence_fd unmodified on interrupted wait
    On Fri, Jan 27, 2023 at 12:31 AM Ryan Neph <ryanneph@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@chromium.org>

    Reviewed-by: Rob Clark <robdclark@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
    >

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