linux-kernel - Re: lockdep and oops_in

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Message-ID: <AANLkTinR6gvFdN5f60_kMXMv-0m8Dd2tnGZ+WotjbCQX@mail.gmail.com>
Date:	Thu, 23 Sep 2010 13:57:33 +1000
From:	Dave Airlie <airlied@...il.com>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: lockdep and oops_in_progress

On Fri, Aug 6, 2010 at 12:59 AM, Yong Zhang <yong.zhang0@...il.com> wrote:
> On Thu, Aug 05, 2010 at 10:10:49AM +0200, Peter Zijlstra wrote:
>> On Thu, 2010-08-05 at 16:21 +1000, Dave Airlie wrote:
>> > Hi guys,
>> >
>> > I was debugging a wierd issue with suspend/resume and fbcon/X with
>> > some recent work Jesse and myself did to try and make sure a pinned
>> > fbcon always gets the text on it with a panic or oops occurs.
>> >
>> > It does this by testing the oops_in_progress flag, however once any
>> > lockdep issue occurs it looks to me that we leave this flag set
>> > forever, in most places I can see in oops code etc they call
>> > bust_spinlocks(1) then bust_spinlocks(0) to balance the
>> > oops_in_progress value, but lockdep never seems to reset it.
>> >
>> > I'm wondering if there is an inherent reason for this or if I whip up
>> > a patch to reset once the lockdep is printed if this would cause any
>> > issues?
>>
>> That's debug_locks_off(), right? I don't think there's a particular
>> reason we keep it set, cleaning that up might take a bit of work but
>> shouldn't be too hard.
>
> commit e0fdace10e75dac67d906213b780ff1b1a4cc360
> Author: David Miller <davem@...emloft.net>
> Date:   Fri Aug 1 01:11:22 2008 -0700
>
>    debug_locks: set oops_in_progress if we will log messages.
>
>    Otherwise lock debugging messages on runqueue locks can deadlock the
>    system due to the wakeups performed by printk().
>
>    Signed-off-by: David S. Miller <davem@...emloft.net>
>    Signed-off-by: Ingo Molnar <mingo@...e.hu>
>
> Seems we can revert that commit now because of 'robustify printk'.
>
> Dave, what do you think about it?

DaveM ping?

I should probably just push for the revert if printk is robust enough now.

Dave.
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