linux-kernel - Re: Linux 2.6.22-rc4

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Date:	Wed, 6 Jun 2007 00:01:14 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-pm@...ts.linux-foundation.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Linux 2.6.22-rc4

On Tuesday, 5 June 2007 22:19, Pavel Machek wrote:
> Hi!
> 
> > > > [ 116.733327] PM: suspend-to-disk mode set to 'shutdown' [ 
> > > > 116.738849] swsusp: Basic memory bitmaps created [ 116.745353] 
> > > > Stopping tasks ... WARNING: at 
> > > > /home/devel/linux-git/kernel/lockdep.c:2414 check_flags()
> > 
> > > > [  116.755052] irq event stamp: 69
> > > > [  116.755060] hardirqs last  enabled at (69): [<c04040f9>] syscall_exit_work+0x11/0x26
> > > > [  116.755084] hardirqs last disabled at (68): [<c0403fdd>] syscall_exit+0x9/0x1a
> > > > [  116.755109] softirqs last  enabled at (0): [<c042150c>] copy_process+0x4dd/0x1286
> > > > [  116.755139] softirqs last disabled at (0): [<00000000>] 0x0
> > > > [  116.945776] done.
> > 
> > > Well, it's harmless in the sense that "yeah, the system still works", 
> > > but it does seem to be a real bug. We have hardware interrupts 
> > > disabled when we _think_ we should have them on, so our irq tracking 
> > > is off.
> > > 
> > > Ingo, do you see what's up? It looks like we got a signal to a process 
> > > that just got created, is the setup stuff for "tsk->hardirqs_enabled" 
> > > perhaps off a bit?
> > 
> > hm. I cannot see the source of the bug at the moment, but here's my 
> > analysis so far:
> > 
> > the last event that irqtrace got was #69, and that was a 'hardirqs on' 
> > in syscall_exit_work. After that we did a 'hardirqs off' without 
> > properly tracking that via irqtrace. Next time we got an irqtrace event 
> > (event 70) the assert caught up with us and turned off lockdep and 
> > backed out of that function. This was in:
> > 
> >  > [  116.754957]  [<c043c3e5>] check_flags+0x95/0x143
> >  > [  116.754967]  [<c043f158>] lock_acquire+0x29/0x82
> >  > [  116.754977]  [<c06313a7>] _spin_lock+0x35/0x42
> >  > [  116.754990]  [<c044894a>] refrigerator+0x14/0xc6
> >  > [  116.755002]  [<c042d4b3>] get_signal_to_deliver+0x33/0x397
> >  > [  116.755016]  [<c0403597>] do_notify_resume+0x94/0x6ed
> >  > [  116.755029]  [<c0404099>] work_notifysig+0x13/0x1a
> > 
> > isnt the refrigerator() suspend related? Perhaps suspend disables irqs 
> > somewhere that we forgot to track?
> 
> refrigerator is suspend related, but I do not think it does any
> interrupt magic. We do magic later in hibernation process.
> 
> This is in kernel/power/process.c, we have spinlock_irqsave there, but
> that's pretty much it AFAICT.

That's correct.  We don't manipulate IRQs directly in the freezer.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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