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

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Message-ID: <CAK5sBcG5R6kyUydpGB_mQy5oFy-D_5hNuGnAiiJbWRiX_s_Mgg@mail.gmail.com>
Date:	Fri, 4 Jul 2014 10:40:30 +0530
From:	Sachin Kamat <spk.linux@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	"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 10:08 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> 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

This patch fixes boot issue on Exynos5420/5800 based boards with bL
switcher enabled.

FWIW,
Tested-by: Sachin Kamat <sachin.kamat@...sung.com>

-- 
Regards,
Sachin.
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