linux-kernel - Re: [PATCH 2/6] irq_work: Implement remote queueing

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Date:	Wed, 25 Jun 2014 18:38:20 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Kevin Hilman <khilman@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>
Subject: Re: [PATCH 2/6] irq_work: Implement remote queueing

On Wed, Jun 25, 2014 at 10:23:21AM -0600, Stephen Warren wrote:
> On 06/25/2014 04:19 AM, Peter Zijlstra wrote:
> > On Wed, Jun 25, 2014 at 03:24:11PM +0530, Srivatsa S. Bhat wrote:
> >> Wait, that was a stupid idea. hotplug_cfd() already invokes irq_work_run
> >> indirectly via flush_smp_call_function_queue(). So irq_work_cpu_notify()
> >> doesn't need to invoke it again, AFAIU. So perhaps we can get rid of
> >> irq_work_cpu_notify() altogether?
> > 
> > Just so...
> > 
> > getting up at 6am and sitting in an airport terminal doesn't seem to
> > agree with me; any more silly fail here?
> > 
> > ---
> > Subject: irq_work: Remove BUG_ON in irq_work_run()
> > From: Peter Zijlstra <peterz@...radead.org>
> > Date: Wed Jun 25 07:13:07 CEST 2014
> > 
> > Because of a collision with 8d056c48e486 ("CPU hotplug, smp: flush any
> > pending IPI callbacks before CPU offline"), which ends up calling
> > hotplug_cfd()->flush_smp_call_function_queue()->irq_work_run(), which
> > is not from IRQ context.
> > 
> > And since that already calls irq_work_run() from the hotplug path,
> > remove our entire hotplug handling.
> 
> Tested-by: Stephen Warren <swarren@...dia.com>
> 
> [with the s/static// already mentioned in this thread, obviously:-)]

Right; I pushed out a fixed version right before loosing my tubes at the
airport :-)

https://git.kernel.org/cgit/linux/kernel/git/peterz/queue.git/commit/?h=timers/nohz&id=921d8b81281ecdca686369f52165d04fa3505bd7

I've not gotten wu build bot spam on it so it must be good ;-)

In any case, I'll add your tested-by and update later this evening.
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