linux-kernel - Re: drm: GPF in drm

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Date:   Mon, 28 Nov 2016 09:41:56 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Michel Dänzer <michel@...nzer.net>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        David Herrmann <dh.herrmann@...il.com>,
        syzkaller <syzkaller@...glegroups.com>,
        David Airlie <airlied@...ux.ie>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: drm: GPF in drm_getcap

On Mon, Nov 28, 2016 at 8:14 AM, Michel Dänzer <michel@...nzer.net> wrote:
> On 28/11/16 03:55 PM, Daniel Vetter wrote:
>> On Sat, Nov 26, 2016 at 7:22 PM, David Herrmann <dh.herrmann@...il.com> wrote:
>>> On Sat, Nov 26, 2016 at 7:07 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>>>> grep "card0" dmesg:
>>>> [    5.298617] device: 'card0': device_add
>>>> [    5.298946] PM: Adding info for No Bus:card0
>>>> [    6.436178] device: 'card0': device_add
>>>> [    6.436488] PM: Adding info for No Bus:card0
>>>>
>>>>
>>>> # ls -l /dev/dri/card0
>>>> crw-rw---T 1 root video 226, 0 Nov 26 18:05 /dev/dri/card0
>>>>
>>>> # ls -lt /sys/class/drm/card0/device/
>>>> ls: cannot access /sys/class/drm/card0/device/: No such file or directory
>>>>
>>>> # ls -lt /sys/class/drm/card0/device/driver
>>>> ls: cannot access /sys/class/drm/card0/device/driver: No such file or directory
>>>
>>> Looks like vgem. Something like this should help:
>>>
>>>     https://gist.github.com/dvdhrm/1bcdf4f3485aa1614a0198a7b90515e2
>>>
>>> I wonder whether it would be more appropriate to return -ENOTSUPP rather than 0.
>
> Can't see how that would matter FWIW.
>
>
>> Seems a bit overkill, but can't hurt. This is most likely a
>> regression, probably introduced in
>>
>> commit f837297ad82480024d3ad08cd84f6670bcafa862
>> Author: Michel Dänzer <michel.daenzer@....com>
>> Date:   Mon Aug 8 16:23:39 2016 +0900
>>
>>     drm: Add DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE/RELATIVE flags v2
>>
>> Michel, can you pls take care of this? Either with a minimal fix, or
>> by adopting David's patch?
>
> Can't we just use David's patch as-is? If not, I think Dmitry or someone
> else would be better equipped than me to extract a minimal fix from it
> and test it.


I know nothing about DRM code. Reproducer is attached to the first email.