linux-kernel - Re: 2.6.30: hibernation/swsusp lockup due to acpi-cpufreq

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Date:	Tue, 16 Jun 2009 11:55:40 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Johannes Stezenbach <js@...21.net>
Cc:	rjw@...k.pl, linux-kernel@...r.kernel.org, davej@...hat.com,
	pavel@....cz, linux-acpi@...r.kernel.org, lenb@...nel.org,
	venkatesh.pallipadi@...el.com, arjan@...radead.org,
	tglx@...utronix.de
Subject: Re: 2.6.30: hibernation/swsusp lockup due to acpi-cpufreq

On Tue, 16 Jun 2009 16:22:17 +0200
Johannes Stezenbach <js@...21.net> wrote:

> Fix swsusp failure on !SMP
> 
> Commit 01599fca6758d2cd133e78f87426fc851c9ea725 introduced
> a regression which caused a backtrace on suspend and
> a hang on resume on a Thinkpad T42p (Pentium M CPU).
> 
> Signed-off-by: Johannes Stezenbach <js@...21.net>
> 
> 
> --- linux-2.6.30/kernel/up.c.orig	2009-06-16 15:56:28.000000000 +0200
> +++ linux-2.6.30/kernel/up.c	2009-06-16 15:57:27.000000000 +0200
> @@ -10,11 +10,13 @@
>  int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
>  				int wait)
>  {
> +	unsigned long flags;
> +
>  	WARN_ON(cpu != 0);
>  
> -	local_irq_disable();
> +	local_irq_save(flags);
>  	(func)(info);
> -	local_irq_enable();
> +	local_irq_restore(flags);
>  
>  	return 0;
>  }

ok, what's going on here?  The patch implies that someone (presumably
acpi-cpufreq) is calling smp_call_function_single() with local
interrupts disabled.  That's a bug on SMP kernels.  And it'll generate
a trace if it happens:

	/* Can deadlock when called with interrupts disabled */
	WARN_ON_ONCE(irqs_disabled() && !oops_in_progress);

but nobody has reported such a trace AFAIK?

Also, prior to 01599fca6758d2cd133e78f87426fc851c9ea725, acpi-cpufreq
was using work_on_cpu().  If it was calling work_on_cpu() with local
interrupts disabled then that would have been a bug too, which could
generate might_sleep() or scheduling-while-atomic warnings.

Because it is a bug to call the SMP version of
smp_call_function_single() with local interrupts disabled, I don't
think we should need to apply the above patch.

But I don't know what we _should_ do because I don't know what the bug
is.  Are you able to get us a copy of that stack trace?

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