Re: [PATCH 1/3] drm/sti: do not remove the drm_bridge that was never added

Daniel Vetter
2018-05-07T13:39:37Z

On Thu, May 03, 2018 at 11:12:21PM +0200, Peter Rosin wrote:
> On 2018-05-03 11:06, Daniel Vetter wrote:
> > On Wed, May 02, 2018 at 09:40:23AM +0200, Peter Rosin wrote:
> >> The more natural approach would perhaps be to add an drm_bridge_add,
> >> but there are several other bridges that never call drm_bridge_add.
> >> Just removing the drm_bridge_remove is the easier fix.
> >>
> >> Signed-off-by: Peter Rosin <peda@axentia.se>
> >
> > This mess is much bigger. There's 2 pairs of bridge functions:
> >
> > - drm_bridge_attach/detach. Those are meant to be called by the overall
> > drm driver to connect/disconnect a drm_bridge.
> >
> > - drm_bridge_add/remove. These are supposed to be called by the bridge
> > driver itself to register/unregister itself. Maybe we should rename
> > them, since the same issue happens with drm_panel, with the same
> > confusion.
> >
> > I thought someone was working on a cleanup series to fix this mess, but I
> > didn't find anything.
>
> Ok, I just spotted the imbalance and didn't really dig into what
> actually happens in these error paths. Now that I have done so I
> believe that the removed drm_bridge_remove calls causes NULL
> dereferences if/when the error paths are triggered.
>
> So, I don't think this can wait for some bigger cleanup.
>
> drm_bridge_remove calls list_del_init calls __list_del_entry calls
> __list_del with NULL in both prev and next since the list member
> is never initialized. prev and next are dereferenced by __list_del
> and you have *boom*
>
> I recommend adding the tag
>
> Fixes: 84601dbdea36 ("drm: sti: rework init sequence")
>
> so that stable picks this one up.

I just wanted to correct your commit message text - the correct solution
is definitely _not_ for sti here to call drm_bridge_add. It should call
drm_bridge_attach/detach only, as a pair.

I didn't check whether you instead have a _detach call missing or what's
going on here.
-Daniel
>
> Cheers,
> Peter
>
> > -Daniel
> >
> >> ---
> >> drivers/gpu/drm/sti/sti_hda.c | 1 -
> >> drivers/gpu/drm/sti/sti_hdmi.c | 1 -
> >> 2 files changed, 2 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/sti/sti_hda.c b/drivers/gpu/drm/sti/sti_hda.c
> >> index 67bbdb49fffc..199db13f565c 100644
> >> --- a/drivers/gpu/drm/sti/sti_hda.c
> >> +++ b/drivers/gpu/drm/sti/sti_hda.c
> >> @@ -721,7 +721,6 @@ static int sti_hda_bind(struct device *dev, struct device *master, void *data)
> >> return 0;
> >>
> >> err_sysfs:
> >> - drm_bridge_remove(bridge);
> >> return -EINVAL;
> >> }
> >>
> >> diff --git a/drivers/gpu/drm/sti/sti_hdmi.c b/drivers/gpu/drm/sti/sti_hdmi.c
> >> index 58f431102512..932724784942 100644
> >> --- a/drivers/gpu/drm/sti/sti_hdmi.c
> >> +++ b/drivers/gpu/drm/sti/sti_hdmi.c
> >> @@ -1315,7 +1315,6 @@ static int sti_hdmi_bind(struct device *dev, struct device *master, void *data)
> >> return 0;
> >>
> >> err_sysfs:
> >> - drm_bridge_remove(bridge);
> >> hdmi->drm_connector = NULL;
> >> return -EINVAL;
> >> }
> >> --
> >> 2.11.0
> >>
> >> _______________________________________________
> >> dri-devel mailing list
> >> dri-devel@lists.freedesktop.org
> >> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> >
>
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--
Daniel Vetter
Software Engineer, Intel Corporation