linux-kernel - Re: [PATCH] drm/virtio: fix command submission with objects but without fence.

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Date:   Thu, 5 Sep 2019 10:14:20 -0700
From:   Chia-I Wu <olvaffe@...il.com>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     ML dri-devel <dri-devel@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@...ts.linux-foundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/virtio: fix command submission with objects but
 without fence.

On Wed, Sep 4, 2019 at 10:23 PM Gerd Hoffmann <kraxel@...hat.com> wrote:
>
> On Wed, Sep 04, 2019 at 04:10:30PM -0700, Chia-I Wu wrote:
> > On Wed, Sep 4, 2019 at 12:48 AM Gerd Hoffmann <kraxel@...hat.com> wrote:
> > >
> > > Only call virtio_gpu_array_add_fence if we actually have a fence.
> > >
> > > Fixes: da758d51968a ("drm/virtio: rework virtio_gpu_execbuffer_ioctl fencing")
> > > Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
> > > ---
> > >  drivers/gpu/drm/virtio/virtgpu_vq.c | 9 +++++----
> > >  1 file changed, 5 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
> > > index 595fa6ec2d58..7fd2851f7b97 100644
> > > --- a/drivers/gpu/drm/virtio/virtgpu_vq.c
> > > +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
> > > @@ -339,11 +339,12 @@ static void virtio_gpu_queue_fenced_ctrl_buffer(struct virtio_gpu_device *vgdev,
> > >                 goto again;
> > >         }
> > >
> > > -       if (fence)
> > > +       if (fence) {
> > >                 virtio_gpu_fence_emit(vgdev, hdr, fence);
> > > -       if (vbuf->objs) {
> > > -               virtio_gpu_array_add_fence(vbuf->objs, &fence->f);
> > > -               virtio_gpu_array_unlock_resv(vbuf->objs);
> > > +               if (vbuf->objs) {
> > > +                       virtio_gpu_array_add_fence(vbuf->objs, &fence->f);
> > > +                       virtio_gpu_array_unlock_resv(vbuf->objs);
> > > +               }
> > This leaks when fence == NULL and vbuf->objs != NULL (which can really
> > happen IIRC... not at my desk to check).
>
> Yes, it can happen, for example when flushing dumb buffers.
>
> But I don't think we leak in this case.  The code paths which don't need
> a fence also do not call virtio_gpu_array_lock_resv(), so things are
> balanced.  The actual release of the objs happens in
> virtio_gpu_dequeue_ctrl_func() via virtio_gpu_array_put_free_delayed().
I misread and thought this was in virtio_gpu_dequeue_ctrl_func.  Sorry :(

Reviewed-by: Chia-I Wu <olvaffe@...il.com>



>
> cheers,
>   Gerd
>