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

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Message-ID: <Pine.LNX.4.64.0804080030500.3896@jikos.suse.cz>
Date:	Tue, 8 Apr 2008 00:33:48 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Andi Kleen <andi@...stfloor.org>,
	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 Tue, 8 Apr 2008, Rafael J. Wysocki wrote:

> > 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.

So, any idea why mce_resume() -> mce_init() -> debug_smp_processor_id() 
triggers the warning? Apparently preempt_count is zero, irqs_disabled() 
returns false, and cpumask_of_cpu() is not equal to current->cpus_allowed.

So there clearly is a bug somewhere.

> > 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.

Is that really relevant here? We still could be switched over to another 
CPU, and that would break things.

-- 
Jiri Kosina
SUSE Labs
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