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

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Message-ID: <53B3086D.8050600@wwwdotorg.org>
Date:	Tue, 01 Jul 2014 13:13:49 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Peter Zijlstra <peterz@...radead.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
CC:	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 06/25/2014 10:23 AM, 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:-)]

next-20140701 still seems to fail CPU hotplug. I assume this patch
hasn't yet been applied for some reason?
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