linux-kernel - RE: [PATCH] Fix the race between smp_call

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Date:	Tue, 13 Mar 2012 16:57:31 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Yanmin Zhang <yanmin_zhang@...ux.intel.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>
Subject: RE: [PATCH] Fix the race between smp_call_function and CPU booting

On Tue, 2012-03-13 at 06:46 +0000, Liu, Chuansheng wrote:
> 
> > -----Original Message-----
> > From: Peter Zijlstra [mailto:peterz@...radead.org]
> > Sent: Monday, March 12, 2012 5:58 PM
> > To: Liu, Chuansheng
> > Cc: linux-kernel@...r.kernel.org; Yanmin Zhang; tglx@...utronix.de
> > Subject: Re: [PATCH] Fix the race between smp_call_function and CPU booting
> > 
> > On Mon, 2012-03-12 at 09:27 +0000, Liu, Chuansheng wrote:
> > > The solution is just to send smp call to active cpus instead of online
> > > cpus.
> > 
> > BTW, that solution is broken because !active cpus can still be online and
> > actually running stuff, so sending IPIs to them is perfectly fine and actually
> > required.
> > 
> Based on current code base, the IPI can be handled only after the cpu is active, before CPU is active,
> Any sending IPI is meanless.

Not so on the unplug case, we clear active long before we actually go
offline and rebuild sched_domains.
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