linux-kernel - Re: [PATCH] drm/virtgpu: fix double unregistration

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Date:   Tue, 12 Nov 2019 19:03:05 +0800
From:   Chuhong Yuan <hslester96@...il.com>
To:     Chuhong Yuan <hslester96@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Gerd Hoffmann <kraxel@...hat.com>,
        dri-devel@...ts.freedesktop.org,
        virtualization@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH] drm/virtgpu: fix double unregistration

On Tue, Nov 12, 2019 at 5:40 PM Daniel Vetter <daniel@...ll.ch> wrote:
>
> On Sat, Nov 09, 2019 at 03:54:17PM +0800, Chuhong Yuan wrote:
> > drm_put_dev also calls drm_dev_unregister, so dev will be unregistered
> > twice.
> > Replace it with drm_dev_put to fix it.
> >
> > Signed-off-by: Chuhong Yuan <hslester96@...il.com>
>
> Nice catch, I'll apply.
>
> Since this is so confusing, we actually have a todo to remove drm_put_dev
> completely from the codebase (and open-code it with explicit
> unregister+put). Want to do that little patch series to update the
> remaining few drivers and then remove drm_put_dev from core code?
>
> Thanks, Daniel
>

I am sorry that I have to focus on my current project in recent days.
But since this is a problem, I have written a Coccinelle script just now
to find drm_put_dev and open-code it.
I hope this helps.
The script is:

virtual patch

@ drm_put_dev depends on patch exists @
expression dev;
@@

- drm_put_dev(dev);
+ drm_dev_unregister(dev);
+ drm_dev_put(dev);

Regards,
Chuhong
> > ---
> >  drivers/gpu/drm/virtio/virtgpu_drv.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c b/drivers/gpu/drm/virtio/virtgpu_drv.c
> > index 0fc32fa0b3c0..fccc24e21af8 100644
> > --- a/drivers/gpu/drm/virtio/virtgpu_drv.c
> > +++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
> > @@ -138,7 +138,7 @@ static void virtio_gpu_remove(struct virtio_device *vdev)
> >
> >       drm_dev_unregister(dev);
> >       virtio_gpu_deinit(dev);
> > -     drm_put_dev(dev);
> > +     drm_dev_put(dev);
> >  }
> >
> >  static void virtio_gpu_config_changed(struct virtio_device *vdev)
> > --
> > 2.23.0
> >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch