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Date:   Mon, 7 May 2018 15:39:29 +0200
From:   Daniel Vetter <daniel@ffwll.ch>
To:     Peter Rosin <peda@axentia.se>
Cc:     linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org,
        David Airlie <airlied@linux.ie>,
        Seung-Woo Kim <sw0312.kim@samsung.com>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        linux-rockchip@lists.infradead.org,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Kukjin Kim <kgene@kernel.org>, dri-devel@lists.freedesktop.org,
        Vincent Abriou <vincent.abriou@st.com>,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/3] drm/sti: do not remove the drm_bridge that was never
 added
Message-ID: <20180507133929.GG12521@phenom.ffwll.local>
Mail-Followup-To: Peter Rosin <peda@axentia.se>,
        linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org,
        David Airlie <airlied@linux.ie>,
        Seung-Woo Kim <sw0312.kim@samsung.com>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        linux-rockchip@lists.infradead.org,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Kukjin Kim <kgene@kernel.org>, dri-devel@lists.freedesktop.org,
        Vincent Abriou <vincent.abriou@st.com>,
        linux-arm-kernel@lists.infradead.org
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 <20180502074025.12421-2-peda@axentia.se>
 <20180503090648.GG12521@phenom.ffwll.local>
 <bd8d12f7-0c71-c96b-80fa-54de7de39511@axentia.se>
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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
> > 
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch