Re: [PATCH 1/1] drm/sun4i: hdmi: Check for null pointer before cleanup

[Stefan Mavrodiev]

Hi,

On 12/16/19 6:12 PM, Maxime Ripard wrote:
> Hi,
>
> On Mon, Dec 16, 2019 at 04:43:48PM +0200, Stefan Mavrodiev wrote:
> > It's possible hdmi->connector and hdmi->encoder divices to be NULL.
> > This can happen when building as kernel module and you try to remove
> > the module.
> >
> > This patch make simple null check, before calling the cleanup functions.
> >
> > Signed-off-by: Stefan Mavrodiev <stefan@xxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> > index a7c4654445c7..b61e00f2ecb8 100644
> > --- a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> > +++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> > @@ -685,8 +685,10 @@ static void sun4i_hdmi_unbind(struct device *dev, struct device *master,
> >   	struct sun4i_hdmi *hdmi = dev_get_drvdata(dev);
> >
> >   	cec_unregister_adapter(hdmi->cec_adap);
> > -	drm_connector_cleanup(&hdmi->connector);
> > -	drm_encoder_cleanup(&hdmi->encoder);
> > +	if (hdmi->connector.dev)
> > +		drm_connector_cleanup(&hdmi->connector);
> > +	if (hdmi->encoder.dev)
> > +		drm_encoder_cleanup(&hdmi->encoder);
> Hmmm, this doesn't look right. Do you have more information on how you
> can reproduce it?

Just build sun4i_drm_hdmi as module (CONFIG_DRM_SUN4I_HDMI=m). Then try 
to unload the module:

# rmmod sun4i_drm_hdmi

And you get this:

Unable to handle kernel NULL pointer dereference at virtual address 00000000
pgd = 6b032436
[00000000] *pgd=00000000
Internal error: Oops: 5 [#1] SMP ARM
Modules linked in: sun4i_drm_hdmi(-)
CPU: 0 PID: 1081 Comm: rmmod Not tainted 5.5.0-rc1-00030-g6ec417030d93 #33
Hardware name: Allwinner sun7i (A20) Family
PC is at drm_connector_cleanup+0x40/0x208
LR is at sun4i_hdmi_unbind+0x10/0x54 [sun4i_drm_hdmi]
...


I've tested that with sunxi/for-next branch on A20-OLinuXino board.

Best regards,
Stefan

> Maxime