[PATCH v2] drm/virtio: fix resource id creation race

[John Bates]

On Fri, Feb 21, 2020 at 10:37 AM Chia-I Wu <olvaffe at gmail.com> wrote:

> On Fri, Feb 21, 2020 at 3:14 AM John Bates <jbates at chromium.org> 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 at chromium.org>
> Reviewed-by: Chia-I Wu <olvaffe at gmail.com>
> > ---
> >  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
>

Yup, noticed that too :)


>
> >         } else {
> >                 int handle = ida_alloc(&vgdev->resource_ida, GFP_KERNEL);
> > --
> > 2.25.0.265.gbab2e86ba0-goog
> >
> > _______________________________________________
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> > dri-devel at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
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