linux-kernel - Re: [Intel-gfx] [4.2-rc4] acpi|drm|i915: circular locking dependency: acpi_video_get_backlight

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Message-ID: <CA+icZUV-A=ipw+B9-UaDHEGP0EosFdCQYEKzv47WK+-u30A7kQ@mail.gmail.com>
Date:	Fri, 14 Aug 2015 11:33:00 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Hans de Goede <hdegoede@...hat.com>
Cc:	Ville Syrjälä <ville.syrjala@...ux.intel.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Dave Airlie <airlied@...hat.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	intel-gfx <intel-gfx@...ts.freedesktop.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Intel-gfx] [4.2-rc4] acpi|drm|i915: circular locking dependency: acpi_video_get_backlight_type

On Fri, Aug 14, 2015 at 10:24 AM, Hans de Goede <hdegoede@...hat.com> wrote:
> Hi,
>
>
> On 13-08-15 16:33, Hans de Goede wrote:
>>
>> Hi,
>>
>> On 12-08-15 21:26, Ville Syrjälä wrote:
>>>
>>> On Mon, Aug 10, 2015 at 08:29:00PM +0200, Sedat Dilek wrote:
>>>>
>>>> On Sat, Aug 1, 2015 at 2:23 PM, Sedat Dilek <sedat.dilek@...il.com>
>>>> wrote:
>>>>>
>>>>> On Mon, Jul 27, 2015 at 12:33 AM, Sedat Dilek <sedat.dilek@...il.com>
>>>>> wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> this my first build of a 4.2-rcN Linux-kernel and I see this...
>>>>>>
>>>>>
>>>>> Just FYI:
>>>>>
>>>>> I am *not* seeing this with drm-intel-nightly from below url.
>>>>>
>>>>> Also, I plan to test Linux v4.2-rc5.
>>>>>
>>>>
>>>> [ CC Linus ]
>>>>
>>>> Knock Knock Knock.
>>>>
>>>> This issue still remains here (with CONFIG_DRM_I915=m)...
>>>>
>>>> [   18.269792] ======================================================
>>>> [   18.269798] [ INFO: possible circular locking dependency detected ]
>>>> [   18.269805] 4.2.0-rc6-1-iniza-small #1 Not tainted
>>>> [   18.269810] -------------------------------------------------------
>>>> [   18.269816] modprobe/727 is trying to acquire lock:
>>>> [   18.269822]  (init_mutex){+.+.+.}, at: [<ffffffffa0090f2d>]
>>>> acpi_video_get_backlight_type+0x17/0x164 [video]
>>>> [   18.269840]
>>>> [   18.269840] but task is already holding lock:
>>>> [   18.269848]  (&(&backlight_notifier)->rwsem){++++..}, at:
>>>> [<ffffffff810a6519>] __blocking_notifier_call_chain+0x39/0x70
>>>> [   18.269864]
>>>> [   18.269864] which lock already depends on the new lock.
>>>> [   18.269864]
>>>> [   18.269875]
>>>> [   18.269875] the existing dependency chain (in reverse order) is:
>>>> [   18.269884]
>>>> ...
>>>>
>>>> Full dmesg log and kernel-config attached.
>>>>
>>>> Shall I add Rusty and modules/modprobe folks?
>>>
>>>
>>> Just got back from vacation and was greeted by this same lockdep splat.
>>>
>>> On a hunch I reverted
>>>
>>> commit 93a291dfaf9c328ca5a9cea1733af1a128efe890
>>> Author: Hans de Goede <hdegoede@...hat.com>
>>> Date:   Tue Jun 16 16:27:52 2015 +0200
>>>
>>>      ACPI / video: Move backlight notifier to video_detect.c
>>>
>>> and the problem seems to be gone. Hans, any thoughts?
>>
>>
>> Looking into this atm, lockdep clearly is right.
>>
>> Sorry about this I have put a lot of thinking into avoiding
>> these kind of issues with this patch-set, but I did not realize
>> there was another lock "hiding" inside the notifier-chain.
>>
>> Further analysis shows that the lock inside the notifier-chain
>> causes similar problems vs register_count_mutex from
>> drivers/acpi/acpi_video.c. I'm working on a fix for this
>> atm.
>
>
> Heh, look at what I just found (I'm shifting my work focus
> in the direction of nouveau) :
>
> https://bugzilla.redhat.com/show_bug.cgi?id=1152876
>
> So it looks like we have had the root cause of this issue
> for a long time already, maybe my recent backlight selection
> logic cleanup / rework has made it easier to trigger the
> lockdep warning for this though.
>
> Anyhow assuming people are ok with the fix I submitted
> yesterday we've a fix for this now.
>

Yay :-)

- sed@ -

> Regards,
>
> Hans
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