linux-kernel - Re: [PATCH tip/core/rcu 2/3] rcu: make hot-unplugged CPU relinquish its own RCU callbacks

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Message-ID: <20091007135049.GF6838@linux.vnet.ibm.com>
Date:	Wed, 7 Oct 2009 06:50:49 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, Valdis.Kletnieks@...edu, dhowells@...hat.com
Subject: Re: [PATCH tip/core/rcu 2/3] rcu: make hot-unplugged CPU
	relinquish its own RCU callbacks

On Wed, Oct 07, 2009 at 09:16:12AM -0400, Steven Rostedt wrote:
> Paul,
> 
> Still suffering jetlag? ;-)

As a matter of fact, yes.  ;-)

> On Tue, 2009-10-06 at 21:48 -0700, Paul E. McKenney wrote:
> > From: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > 
> > The current interaction between RCU and CPU hotplug requires that
> > RCU block in CPU notifiers waiting for callbacks to drain.  This can
> > be greatly simplified by haing each CPU relinquish its own callbacks,
>                            having
> 
> > and for both _rcu_barrier() and CPU_DEAD notifiers to adopt all callbacks
> > that were previously relinquished.  This change also eliminates the
> > possibility of certain types of hangs due to the previous practice of
> > waiting for callbacks to be invoked from within CPU notifiers.  If you
> > don't every wait, you cannot hang.
>         ever
> 
> ;-)

Courtesy of "git cherry-pick" and my being out of it.  ;-)

							Thanx, Paul

> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> -- Steve
> 
> 
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