linux-kernel - Re: [PATCH v6 14/18] drm/virtio: rework virtio_gpu_transfer_from_host

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Date:   Fri, 5 Jul 2019 11:01:05 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Chia-I Wu <olvaffe@...il.com>
Cc:     ML dri-devel <dri-devel@...ts.freedesktop.org>,
        Gurchetan Singh <gurchetansingh@...omium.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 v6 14/18] drm/virtio: rework
 virtio_gpu_transfer_from_host_ioctl fencing

On Thu, Jul 04, 2019 at 11:55:59AM -0700, Chia-I Wu wrote:
> On Thu, Jul 4, 2019 at 4:48 AM Gerd Hoffmann <kraxel@...hat.com> wrote:
> >
> > On Wed, Jul 03, 2019 at 01:05:12PM -0700, Chia-I Wu wrote:
> > > On Tue, Jul 2, 2019 at 7:19 AM Gerd Hoffmann <kraxel@...hat.com> wrote:
> > > >
> > > > Switch to the virtio_gpu_array_* helper workflow.
> > > (just repeating my question on patch 6)
> > >
> > > Does this fix the obj refcount issue?  When was the issue introduced?
> >
> > obj refcount should be fine in both old and new code.
> >
> > old code:
> >   drm_gem_object_lookup
> >   drm_gem_object_put_unlocked
> >
> > new code:
> >   virtio_gpu_array_from_handles
> >   virtio_gpu_array_put_free (in virtio_gpu_dequeue_ctrl_func).
> >
> > Or did I miss something?
> In the old code, drm_gem_object_put_unlocked is called before the vbuf
> using the object is retired.  Isn't that what object array wants to
> fix?

I think the fence keeps the bo alive.

cheers,
  Gerd