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Date: Wed, 7 Mar 2007 10:16:38 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Tsutomu OWA <tsutomu.owa@toshiba.co.jp>
Subject: Re: [RFC] [patch 4/6 -rt] powerpc 2.6.20-rt8: fix a runtime warnings
	for xmon
Message-ID: <20070307091638.GC1783@elte.hu>
References: <yyi8xe925vg.wl@toshiba.co.jp> <yyi3b4h25jj.wl@toshiba.co.jp>
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* Tsutomu OWA <tsutomu.owa@toshiba.co.jp> wrote:

> @@ -342,6 +342,7 @@ static int xmon_core(struct pt_regs *reg
>  
>  	msr = mfmsr();
>  	mtmsr(msr & ~MSR_EE);	/* disable interrupts */
> +	preempt_disable();

i'm not an xmon expert, but maybe it might make more sense to first 
disable preemption, then interrupts - otherwise you could be preempted 
right after having disabled these interrupts (and be scheduled to 
another CPU, etc.). What is the difference between local_irq_save() and 
the above 'disable interrupts' sequence? If it's not the same and 
xmon_core() relied on having hardirqs disabled then it might make sense 
to do a local_irq_save() there, instead of a preempt_disable().

	Ingo