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

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Message-ID: <20120825161806.GD3436@linux.vnet.ibm.com>
Date:	Sat, 25 Aug 2012 09:18:06 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ben Hutchings <ben@...adent.org.uk>,
	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>,
	Michael Cree <mcree@...on.net.nz>
Subject: Re: [PATCH 00/11] rcu: Add missing RCU idle APIs on idle loop v2

On Sat, Aug 25, 2012 at 03:16:49PM +0200, Frederic Weisbecker wrote:
> On Fri, Aug 24, 2012 at 08:50:47PM -0700, Paul E. McKenney wrote:
> > On Sat, Aug 25, 2012 at 02:19:14AM +0100, 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.
> > 
> > OK, if any of the arch maintainers wishes to submit the patch to 3.6,
> > they are free to do so -- just let me know and I will drop the patch from
> > my tree.
> > 
> > That said, all this does is cause spurious warnings to be printed, so
> > not sure it really qualifies as serious.  But I am happy to leave that
> > decision with the individual arch maintainers -- it is their arch,
> > after all, so their decision.
> 
> Couldn't that cause hung tasks due to long lasting synchronize_rcu() ?

In theory, definitely.  In practice, they haven't been running into it,
or they would be reporting hangs.

							Thanx, Paul

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