On Thu, Feb 13, 2020 at 3:18 PM Gurchetan Singh
<gurchetansingh@xxxxxxxxxxxx> wrote:
>
> Use an atomic variable to track whether a context has been
> initiated.
>
> v2: Fix possible race (@olv)
>
> Signed-off-by: Gurchetan Singh <gurchetansingh@xxxxxxxxxxxx>
> ---
> drivers/gpu/drm/virtio/virtgpu_drv.h | 1 +
> drivers/gpu/drm/virtio/virtgpu_ioctl.c | 3 +++
> drivers/gpu/drm/virtio/virtgpu_kms.c | 1 +
> 3 files changed, 5 insertions(+)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
> index 72c1d9b59dfe..ca505984f8ab 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_drv.h
> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
> @@ -209,6 +209,7 @@ struct virtio_gpu_device {
>
> struct virtio_gpu_fpriv {
> uint32_t ctx_id;
> + atomic_t context_initiated;
> };
>
> /* virtio_ioctl.c */
> diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> index 896c3f419a6d..a98884462944 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> @@ -44,6 +44,9 @@ void virtio_gpu_create_context(struct drm_device *dev,
> if (!vgdev->has_virgl_3d)
> return;
>
> + if (!atomic_add_unless(&vfpriv->context_initiated, 1, 1))
> + return;
> +
How does this work? When thread A and B enter this function at the
same time, and thread B returns early, it is possible that thread B
queues other commands before thread A has the chance to queue
virtio_gpu_cmd_context_create.
> get_task_comm(dbgname, current);
> virtio_gpu_cmd_context_create(vgdev, vfpriv->ctx_id,
> strlen(dbgname), dbgname);
> diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c
> index 282558576527..25248bad3fc4 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_kms.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_kms.c
> @@ -263,6 +263,7 @@ int virtio_gpu_driver_open(struct drm_device *dev, struct drm_file *file)
> }
>
> vfpriv->ctx_id = handle + 1;
> + atomic_set(&vfpriv->context_initiated, 0);
> file->driver_priv = vfpriv;
> virtio_gpu_create_context(dev, file);
> return 0;
> --
> 2.25.0.265.gbab2e86ba0-goog
>
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