linux-kernel - Re: [PATCH 05/32] nohz: Move rcu dynticks idle mode handling to idle enter/exit APIs

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Date:	Tue, 30 Aug 2011 13:17:42 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>,
	Avi Kivity <avi@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Menage <menage@...gle.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>
Subject: Re: [PATCH 05/32] nohz: Move rcu dynticks idle mode handling to
 idle enter/exit APIs

On Tue, 2011-08-30 at 01:35 +0200, Frederic Weisbecker wrote:
> But rcu read side critical sections (preemption disabled, rcu_read_lock(),
> softirq disabled) don't need the tick to enforce the critical section
> itself. 

Note that with PREEMPT_RCU only the rcu_read_lock() is actually an rcu
read side critical section, non of the others should be used as such.
Relying on preempt_disable(), local_bh_disable() and similar is broken
as per a long while ago.


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