Re: [PATCH -V2] drm/sun4i: Grab reference of connector before return connector from sun4i_tcon_get_connector

[He Ying]

在 2021/11/2 23:03, Maxime Ripard 写道:
> Hi,
>
> On Tue, Nov 02, 2021 at 04:46:28AM -0400, He Ying wrote:
> >  From the comments of drm_for_each_connector_iter(), we know
> > that "connector is only valid within the list body, if you
> > want to use connector after calling drm_connector_list_iter_end()
> > then you need to grab your own reference first using
> > drm_connector_get()". So fix the wrong use of connector
> > according to the comments and then call drm_connector_put()
> > after using connector finishes.
> >
> > Signed-off-by: He Ying <heying24@xxxxxxxxxx>
> > ---
> >
> > V2:
> >   Use proper subject prefix
> >
> >   drivers/gpu/drm/sun4i/sun4i_tcon.c | 18 +++++++++++++-----
> >   1 file changed, 13 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > index 9f06dec0fc61..24fa6784ee5f 100644
> > --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > @@ -47,12 +47,12 @@ static struct drm_connector *sun4i_tcon_get_connector(const struct drm_encoder *
> >   	drm_connector_list_iter_begin(encoder->dev, &iter);
> >   	drm_for_each_connector_iter(connector, &iter)
> >   		if (connector->encoder == encoder) {
> > -			drm_connector_list_iter_end(&iter);
> > -			return connector;
> > +			drm_connector_get(connector);
> > +			break;
> >   		}
> >   	drm_connector_list_iter_end(&iter);
> >   
> > -	return NULL;
> > +	return connector;
> Connector might be uninitialized if we don't find one here

Connector should be NULL if we don't find one. The code is

#define drm_for_each_connector_iter(connector, iter) \
   while ((connector = drm_connector_list_iter_next(iter)))

So, when we don't break from the while body, connector

can only be NULL.

> >   }
> >   
> >   static int sun4i_tcon_get_pixel_depth(const struct drm_encoder *encoder)
> > @@ -65,6 +65,7 @@ static int sun4i_tcon_get_pixel_depth(const struct drm_encoder *encoder)
> >   		return -EINVAL;
> >   
> >   	info = &connector->display_info;
> > +	drm_connector_put(connector);
> >   	if (info->num_bus_formats != 1)
> We're still accessing connector->display_info here, but it might have been
> freed already.
Agree. I'll place it after using 'info' finishes in v3.
> Maxime