linux-kernel - Re: [PATCH] time: add an offline-cpu check in add_timer

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Date:	Fri, 14 Dec 2007 12:05:03 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andi Kleen <andi@...stfloor.org>
cc:	miaox@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] time: add an offline-cpu check in add_timer_on()

On Fri, 14 Dec 2007, Andi Kleen wrote:

> Miao Xie <miaox@...fujitsu.com> writes:
> 
> > Hi everyone,
> >   I think we need a check in the function add_timer_on() to avoid adding a
> > timer into the timer list of an offline cpu.
> >
> > This patch fixes this problem in add_timer_on().
> 
> No it doesn't -- it will just crash if a caller does that. If it's a real 
> problem then you either need to fix the callers or change add_timer_on()
> to transparently put it onto another CPU.
> 
> I don't think it's a real problem though because CPU offlining does
> a stop machine and that should take care of most such races.

No. CPU offlining does not prevent code to try inserting a timer on a
offlined CPU. If there is a real problem with this we need to fix the
calling code. We should not insert it somewhere else magically.

Thanks,

	 tglx
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