linux-kernel - Re: oprofile can cause an NMI to schedule (was: [RT] scheduling and oprofile)

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Date:	Wed, 25 Oct 2006 15:52:59 -0400
From:	Lee Revell <rlrevell@...-job.com>
To:	Mike Kravetz <kravetz@...ibm.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	John Levon <levon@...ementarian.org>, phil.el@...adoo.fr,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	oprofile-list@...ts.sourceforge.net, george@...sta.com
Subject: Re: oprofile can cause an NMI to schedule (was: [RT] scheduling
	and oprofile)

On Wed, 2006-10-25 at 11:58 -0700, Mike Kravetz wrote:
> Newer RT kernels (such as linux-2.6.18-rt5) have reenabled the
> add_preempt_count/sub_preempt_count calls in nmi_enter/exit.  If I
> understand correctly the reason one could not modify the preempt_count
> from NMI code is that it could have been in the process of being
> modified by non-NMI code.  But, in recent RT kernels it appears that
> preempt_count is still a single word modified by both NMI and
> non-NMI code.  What am I missing that now makes this safe?
> 

It's not safe.  NMI causes hard lockups on 2.6.18-rt5.  Get 2.6.18-rt7.

Lee

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