linux-kernel - Re: [PATCH 00/11] rcu: Add missing RCU idle APIs on idle loop v2

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Date:	Sat, 25 Aug 2012 14:10:17 +1200
From:	Michael Cree <mcree@...on.net.nz>
To:	Ben Hutchings <ben@...adent.org.uk>
CC:	paulmck@...ux.vnet.ibm.com,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Chris Zankel <chris@...kel.net>,
	"3.2.x.." <stable@...r.kernel.org>,
	Chen Liqin <liqin.chen@...plusct.com>,
	Lennox Wu <lennox.wu@...il.com>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Helge Deller <deller@....de>,
	Parisc <linux-parisc@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	Koichi Yasutake <yasutake.koichi@...panasonic.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	m68k <linux-m68k@...ts.linux-m68k.org>,
	Hirokazu Takata <takata@...ux-m32r.org>,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	Mikael Starvik <starvik@...s.com>,
	Jesper Nilsson <jesper.nilsson@...s.com>,
	Cris <linux-cris-kernel@...s.com>,
	Richard Henderson <rth@...ddle.net>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Matt Turner <mattst88@...il.com>,
	alpha <linux-alpha@...r.kernel.org>
Subject: Re: [PATCH 00/11] rcu: Add missing RCU idle APIs on idle loop v2

On 25/08/12 13:19, Ben Hutchings wrote:
> On Fri, 2012-08-24 at 14:26 -0700, Paul E. McKenney wrote:
>> On Thu, Aug 23, 2012 at 04:58:24PM +0200, Frederic Weisbecker wrote:
>>> Hi,
>>>
>>> Changes since v1:
>>>
>>> - Fixed preempt handling in alpha idle loop
>>> - added ack from Geert
>>> - fixed stable email address, sorry :-/
>>>
>>> This time I built tested everywhere but: h8300 (compiler internal error),
>>> and mn10300, parisc, score (cross compilers not available in
>>> ftp://ftp.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.6.3/)
>>>
>>> For testing, you can pull from:
>>>
>>> git://github.com/fweisbec/linux-dynticks.git
>>> 	rcu/idle-fix-v2 
>>>
>>> Thanks.
>>
>> I have queued these on -rcu branch rcu/idle:
>>
>> 	git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
>>
>> This problem has been in place since 3.3, so it is hard to argue that
>> it is a regression for this merge window.  I have therefore queued it
>> for 3.7.
> 
> I don't follow that; I would expect any serious bug fix (serious enough
> for a stable update) to be acceptable for 3.6 at this point.
> 
> If the regression occurred in 3.3, then the cc lines should be something
> like:
> 
>     Cc: <stable@...r.kernel.org> # 3.3+
> 
> and not the current:
> 
>     Cc: 3.2.x.. <stable@...r.kernel.org>

The Alpha patches fix an even earlier regression resulting in RCU CPU
stalls on an SMP kernel built for generic Alpha (which includes the
current Debian 3.2-alpha-smp kernel) and renders the kernel pretty much
unuseable.  I've only tested the two alpha patches together but maybe
just the first patch (1/11 alpha: Fix preemption handling in idle loop)
might be needed to fix the problem in 3.2.   I'll test and let you know.

Cheers
Michael.
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