linux-kernel - Re: [PATCH] drm: Check for connector->state NULL in drm_atomic_add_affected

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Date:	Mon, 7 Mar 2016 16:09:06 -0800
From:	Doug Anderson <dianders@...omium.org>
To:	Douglas Anderson <dianders@...omium.org>,
	David Airlie <airlied@...ux.ie>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Tomasz Figa <tfiga@...omium.org>,
	姚智情 <mark.yao@...k-chips.com>,
	Heiko Stübner <heiko@...ech.de>
Subject: Re: [PATCH] drm: Check for connector->state NULL in drm_atomic_add_affected_connectors

Hi,

On Mon, Mar 7, 2016 at 4:05 PM, Doug Anderson <dianders@...omium.org> wrote:
> Daniel,
>
> On Sun, Mar 6, 2016 at 8:29 AM, Daniel Vetter <daniel@...ll.ch> wrote:
>> On Fri, Mar 04, 2016 at 03:43:53PM -0800, Douglas Anderson wrote:
>>> On a system I'm doing development on I found a crash.  The crawl looked
>>> like:
>>>
>>>   PC is at drm_atomic_add_affected_connectors+0x98/0xe8
>>>   ...
>>>   drm_atomic_add_affected_connectors from __drm_atomic_helper_set_config+0x218/0x344
>>>   __drm_atomic_helper_set_config from restore_fbdev_mode+0x108/0x250
>>>   restore_fbdev_mode from drm_fb_helper_restore_fbdev_mode_unlocked+0x3c/0x80
>>>   drm_fb_helper_restore_fbdev_mode_unlocked from rockchip_drm_lastclose+0x1c/0x20
>>>   rockchip_drm_lastclose from drm_lastclose+0x4c/0x104
>>>   drm_lastclose from drm_release+0x424/0x47c
>>>   drm_release from __fput+0xf8/0x1d4
>>>   __fput from ____fput+0x18/0x1c
>>>   ____fput from task_work_run+0xa8/0xbc
>>>   task_work_run from do_exit+0x448/0x91c
>>>   do_exit from do_group_exit+0x5c/0xcc
>>>   do_group_exit from get_signal+0x4dc/0x57c
>>>   get_signal from do_signal+0x9c/0x3b4
>>>   do_signal from do_work_pending+0x60/0xb8
>>>   do_work_pending from slow_work_pending+0xc/0x20
>>>
>>> I found that I could fix the crash by checking connector->state against
>>> NULL.  This isn't code I'm familiar with and I didn't dig too deep, so
>>> I'd appreciate any opinions about whether this is a sane thing to do.
>>> Note that I don't actually have graphics up on my system at the moment,
>>> so perhaps this is all just a symptom of the strange state I'm in.
>>>
>>> Signed-off-by: Douglas Anderson <dianders@...omium.org>
>>
>> This is a driver bug - under atomic the assumption is that there is
>> _always_ a current software state. Most driver set up the initial
>> "everything off" state in the ->reset functions.
>
> Ah, I see what the problem is.  It looks like the main Rockchip
> subsystem moved to atomic but the patch to support that in dw_hdmi
> never landed.  If I pick <https://patchwork.kernel.org/patch/7868951/>
> then my crash goes away.  :)
>
> In case it's not obvious, please consider $SUBJECT patch abandoned.  Thanks!

Argh.  ...or the needed patch landed but I didn't pick it back in my
backport.  Even dumber.  :(

-Doug