linux-kernel - Re: [patch 61/66] timers: Convert to hotplug state machine

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Date:	Tue, 26 Jul 2016 19:16:38 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	<rcochran@...utronix.de>
CC:	Anna-Maria Gleixner <anna-maria@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"Ingo Molnar" <mingo@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 61/66] timers: Convert to hotplug state machine

Hi Richard,

On 26/07/16 16:42, rcochran@...utronix.de wrote:
> Jon,
> 
> On Mon, Jul 25, 2016 at 03:56:48PM +0100, Jon Hunter wrote:
>>> When tearing down, call timers_dead_cpu before notify_dead.
>>> There is a hidden dependency between:
>>>
>>> - timers
>>> - Block multiqueue
>>> - rcutree
>>>
>>> If timers_dead_cpu() comes later than blk_mq_queue_reinit_notify()
>>> that latter function causes a RCU stall.
>>
>> After this change is applied I am seeing RCU stalls during suspend
>> on Tegra. I guess I am hitting the case mentioned above? How should
>> this be avoided?
> 
> Contrary to the commit message, this callback ended up in the wrong
> place within the sequence.  (It was correct in an earlier version, but
> the series has been through many changes.)
> 
> Can you try this patch to see if it avoids the stall, please?

I have included the patch and I am no longer seeing any RCU stalls and
so this does look like it fixed it.

Thanks!
Jon

-- 
nvpublic