linux-kernel - Re: [PATCH] Prevent going idle with softirq pending

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Message-ID: <20070522050410.GA9295@elte.hu>
Date:	Tue, 22 May 2007 07:04:10 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Linus Torvalds <torvalds@...l.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>,
	David Miller <davem@...emloft.net>,
	Stable Team <stable@...nel.org>,
	Anant Nitya <kernel@...chanda.info>
Subject: Re: [PATCH] Prevent going idle with softirq pending


* Thomas Gleixner <tglx@...utronix.de> wrote:

> The NOHZ patch contains a check for softirqs pending when a CPU goes 
> idle. The BUG is unrelated to NOHZ, it just was made visible by the 
> NOHZ patch. The BUG showed up mainly on P4 / hyperthreading enabled 
> machines which lead the investigations into the wrong direction in the 
> first place. The real cause is in cond_resched_softirq():
> 
> cond_resched_softirq() is enabling softirqs without invoking the 
> softirq daemon when softirqs are pending. This leads to the warning 
> message in the NOHZ idle code:

good find!

>  		raw_local_irq_disable();
> -		_local_bh_enable();
> +		local_bh_enable();
>  		raw_local_irq_enable();

hm, i think this should be done without having irqs disabled?

	Ingo
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