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

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Date:   Thu, 4 Jul 2019 11:55:59 -0700
From:   Chia-I Wu <olvaffe@...il.com>
To:     Gerd Hoffmann <kraxel@...hat.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 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?

We get away with that because the host only sees  hw_res_handles, and
executes the commands in order.

Maybe it was me who missed something..?

>
> cheers,
>   Gerd
>