On Fri, Feb 21, 2020 at 3:14 AM John Bates <jbates@xxxxxxxxxxxx> wrote:
>
> The previous code was not thread safe and caused
> undefined behavior from spurious duplicate resource IDs.
> In this patch, an atomic_t is used instead. We no longer
> see any duplicate IDs in tests with this change.
>
> Fixes: 16065fcdd19d ("drm/virtio: do NOT reuse resource ids")
> Signed-off-by: John Bates <jbates@xxxxxxxxxxxx>
Reviewed-by: Chia-I Wu <olvaffe@xxxxxxxxx>
> ---
> drivers/gpu/drm/virtio/virtgpu_object.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c b/drivers/gpu/drm/virtio/virtgpu_object.c
> index 017a9e0fc3bb..890121a45625 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_object.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_object.c
> @@ -42,8 +42,8 @@ static int virtio_gpu_resource_id_get(struct virtio_gpu_device *vgdev,
> * "f91a9dd35715 Fix unlinking resources from hash
> * table." (Feb 2019) fixes the bug.
> */
> - static int handle;
> - handle++;
> + static atomic_t seqno = ATOMIC_INIT(0);
> + int handle = atomic_inc_return(&seqno);
> *resid = handle + 1;
resid 1 is (was) discriminated :D
> } else {
> int handle = ida_alloc(&vgdev->resource_ida, GFP_KERNEL);
> --
> 2.25.0.265.gbab2e86ba0-goog
>
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