linux-kernel - Re: [stable] [PATCH RFC tip/core/urgent] rcu: Avoid having just-onlined CPU resched itself when RCU is idle

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Date:	Fri, 19 Aug 2011 11:01:37 -0700
From:	Greg KH <greg@...ah.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mathieu.desnoyers@...ymtl.ca,
	laijs@...fujitsu.com, eric.dumazet@...il.com, patches@...aro.org,
	peterz@...radead.org, josh@...htriplett.org, rostedt@...dmis.org,
	stable@...nel.org, dhowells@...hat.com, darren@...art.com,
	niv@...ibm.com, tglx@...utronix.de, dipankar@...ibm.com,
	Valdis.Kletnieks@...edu, mingo@...e.hu, akpm@...ux-foundation.org
Subject: Re: [stable] [PATCH RFC tip/core/urgent] rcu: Avoid having
 just-onlined CPU resched itself when RCU is idle

On Fri, Aug 19, 2011 at 09:35:47AM -0700, Paul E. McKenney wrote:
> CPUs set rdp->qs_pending when coming online to resolve races with
> grace-period start.  However, this means that if RCU is idle, the
> just-onlined CPU might needlessly send itself resched IPIs.  Adjust the
> online-CPU initialization to avoid this, and also to correctly cause
> the CPU to respond to the current grace period if needed.
> 
> This patch is believed to fix or otherwise suppress problems in
> https://bugzilla.redhat.com/show_bug.cgi?id=726877, however, the
> relationship is not apparent to this patch's author.  That said, it is
> hard to argue with test results.
> 
> This will be available from -rcu as soon as kernel.org's mirrors update:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git rcu/urgent
> 
> Reported-by: Nicolas Mailhot <nicolas.mailhot@...oste.net>
> Reported-by: Michal Jaegermann <michal@...ddata.com>
> Reported-by: Josh Boyer <jwboyer@...hat.com>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Tested-by: Josh Boyer <jwboyer@...hat.com>
> 
>  rcutree.c |   11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read Documentation/stable_kernel_rules.txt
for how to do this properly.

</formletter>
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