linux-kernel - Re: [PATCH v5 UPDATEDv3 3/3] CPU hotplug, smp: Flush any pending IPI callbacks before CPU offline

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Message-ID: <20140520102542.GW2485@laptop.programming.kicks-ass.net>
Date:	Tue, 20 May 2014 12:25:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	akpm@...ux-foundation.org, fweisbec@...il.com,
	paulmck@...ux.vnet.ibm.com, tglx@...utronix.de, mingo@...nel.org,
	rusty@...tcorp.com.au, hch@...radead.org, mgorman@...e.de,
	riel@...hat.com, bp@...e.de, rostedt@...dmis.org,
	mgalbraith@...e.de, ego@...ux.vnet.ibm.com, rjw@...ysocki.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 UPDATEDv3 3/3] CPU hotplug, smp: Flush any pending IPI
 callbacks before CPU offline

On Tue, May 20, 2014 at 03:39:59PM +0530, Srivatsa S. Bhat wrote:
> > The multi_cpu_stop() path isn't exclusive to hotplug, so your changelog
> > is wrong or the patch is.
> > 
> 
> Yes, I know that multi_cpu_stop() isn't exclusive to hotplug. That's why
> I have explicitly referred to CPU hotplug in the comment as well as the
> changelog.
> 
> But I totally agree that code-wise this is not the best way to do it since
> this affects (although harmlessly) usecases other than hotplug as well.
> 
> Do you have any other suggestions?

How about making a kernel/smp.c hotplug notifier and stuffing it in the
CPU_DYING list? That's typically after we've already torn down the
interrupts for that cpu, so no chance of any new ones coming in.

Or is that too late?
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