[PATCH 3/4] drm/virtio: track whether or not a context has been initiated

[Chia-I Wu]

On Wed, Feb 12, 2020 at 5:54 PM Gurchetan Singh
<gurchetansingh at chromium.org> wrote:
>
> On Wed, Feb 12, 2020 at 10:50 AM Chia-I Wu <olvaffe at gmail.com> wrote:
> >
> > On Tue, Feb 11, 2020 at 3:56 PM Gurchetan Singh
> > <gurchetansingh at chromium.org> wrote:
> > >
> > > We only want create a new virglrenderer context after the first
> > > 3D ioctl.
> > >
> > > Signed-off-by: Gurchetan Singh <gurchetansingh at chromium.org>
> > > ---
> > >  drivers/gpu/drm/virtio/virtgpu_drv.h   | 1 +
> > >  drivers/gpu/drm/virtio/virtgpu_ioctl.c | 5 +++++
> > >  drivers/gpu/drm/virtio/virtgpu_kms.c   | 2 ++
> > >  3 files changed, 8 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
> > > index edaa7b8224a8..93ce69c0d9be 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 f1afabaa3a08..858ee153fb18 100644
> > > --- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> > > +++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> > > @@ -44,9 +44,14 @@ void virtio_gpu_create_context(struct drm_device *dev,
> > >         if (!vgdev->has_virgl_3d)
> > >                 return;
> > >
> > > +       if (atomic_read(&vfpriv->context_initiated))
> > > +               return;
> > > +
> > >         get_task_comm(dbgname, current);
> > >         virtio_gpu_cmd_context_create(vgdev, vfpriv->ctx_id,
> > >                                       strlen(dbgname), dbgname);
> > > +
> > > +       atomic_inc(&vfpriv->context_initiated);
> > >  }
> > This needs to be protected with a lock.
>
> What do you think about atomic_add_unless(&vfpriv->context_initiated, 1, 1)?
Does that prevent virtio_gpu_cmd_context_create from being called more
than once when two threads call this function at the same time?


>
> > ctx_id can probably be
> > generated here as well.
>
> If we generate the context id in virtio_gpu_create_context, we'll have
> to add error checking in all of the ioctl call-sites (since ida_alloc
> may fail).
>
> int virtio_gpu_create_context(..)
> ret = virtio_gpu_create_context(dev, file);
> if (ret)
>     return -EINVAL
>
> vs.
>
> void virtio_gpu_create_context(..)
> virtio_gpu_create_context(..)
>
> Any strong opinions here?
Yeah, the current way should be better... unless we decide to make
virtio_gpu_cmd_context_create synchronous and check for errors.

>
> >
> > >
> > >  static int virtio_gpu_map_ioctl(struct drm_device *dev, void *data,
> > > diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c
> > > index e1e1c0821a35..64fe5fcbedfd 100644
> > > --- a/drivers/gpu/drm/virtio/virtgpu_kms.c
> > > +++ b/drivers/gpu/drm/virtio/virtgpu_kms.c
> > > @@ -270,7 +270,9 @@ int virtio_gpu_driver_open(struct drm_device *dev, struct drm_file *file)
> > >                 return id;
> > >         }
> > >
> > > +
> > >         vfpriv->ctx_id = id;
> > > +       atomic_set(&vfpriv->context_initiated, 0);
> > >         file->driver_priv = vfpriv;
> > >         virtio_gpu_create_context(dev, file);
> > >
> > > --
> > > 2.25.0.225.g125e21ebc7-goog
> > >