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

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Date:	Wed, 07 Oct 2009 09:16:12 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
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

Paul,

Still suffering jetlag? ;-)

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

;-)

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

-- Steve


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