linux-kernel - Re: lockdep and oops_in

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Message-ID: <20100805145940.GA8685@zhy>
Date:	Thu, 5 Aug 2010 22:59:40 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Dave Airlie <airlied@...il.com>, 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 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?

Thanks,
Yong

> 
> Ingo, do you remember anything about that?, I think that bit comes from
> before my time.
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