linux-kernel - Re: BUG: using smp_processor_id() during suspend with 2.6.25-rc8

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Date:	Tue, 8 Apr 2008 00:29:30 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	Zdenek Kabelac <zdenek.kabelac@...il.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: BUG: using smp_processor_id() during suspend with 2.6.25-rc8

On Tuesday, 8 of April 2008, Andi Kleen wrote:
> On Tue, Apr 08, 2008 at 12:11:17AM +0200, Jiri Kosina wrote:
> > On Tue, 8 Apr 2008, Andi Kleen wrote:
> > 
> > > > I know. However preempt_count is a little bit inconsistent in such cases 
> > > > though.
> > > And? interrupts off beats preempt count anyways. Why did you write the 
> > > patch? Was there a (incorrect) warning triggered?
> > 
> > Reported at http://lkml.org/lkml/2008/4/7/130
> > 
> > BTW is also mce_init() (called from mce_resume()) guaranteed to run with 
> > IRQs off?
> 
> [cc rafael]
> 
> The mce resume is a sysdev.
> 
> sysdevs were always supposed to run completely with interrupts off. If they 
> don't anymore that's some kind of higher level resume code bug which you need 
> to fix there, not hack around in the low level code.

They are executed with interrupts disabled, on one CPU.

> If it does that it likely broke more code too.
> 
> Obviously turning on preemption anywhere around the machine check is
> fatal because it touches CPU state and if you reschedule you could
> switch to another CPU and change or access the wrong CPU's state.

FWIW, at the point when sysdevs are resumed we are single-threaded.

Thanks,
Rafael
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