Date: Thu, 8 Jan 2009 10:30:52 -0500 (EST)
From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
cc: Ingo Molnar <mingo@elte.hu>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       Gregory Haskins <ghaskins@novell.com>, Matthew Wilcox <matthew@wil.cx>,
       Andi Kleen <andi@firstfloor.org>, Chris Mason <chris.mason@oracle.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       linux-fsdevel <linux-fsdevel@vger.kernel.org>,
       linux-btrfs <linux-btrfs@vger.kernel.org>,
       Thomas Gleixner <tglx@linutronix.de>, Nick Piggin <npiggin@suse.de>,
       Peter Morreale <pmorreale@novell.com>,
       Sven Dietrich <SDietrich@novell.com>
Subject: Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning
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On Thu, 8 Jan 2009, Steven Rostedt wrote:
> > > > +	/*
> > > > +	 * We need to validate that we can do a
> > > > +	 * get_cpu() and that we have the percpu area.
> > > > +	 */
> > > > +	if (!cpu_online(cpu))
> > > > +		goto out;
> > > 
> > > Should we need to do a "get_cpu" or something? Couldn't the CPU disappear 
> > > between these two calls. Or does it do a stop-machine and the preempt 
> > > disable will protect us?
> > 
> > Did you miss the preempt_disable() a bit up?
> 
> No, let me rephrase it better. Does the preempt_disable protect against
> another CPU from going off line? Does taking a CPU off line do a 
> stop_machine?

I just looked at the cpu hotplug code, and it does call stop machine. All 
is in order ;-)

-- Steve

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