linux-kernel - Re: [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threads trainwreck

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Message-ID: <20110720213923.GT2313@linux.vnet.ibm.com>
Date:	Wed, 20 Jul 2011 14:39:23 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ben Greear <greearb@...delatech.com>,
	Ed Tomlinson <edt@....ca>, linux-kernel@...r.kernel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, patches@...aro.org,
	edward.tomlinson@...o.bombardier.com
Subject: Re: [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threads
 trainwreck

On Wed, Jul 20, 2011 at 11:05:53PM +0200, Peter Zijlstra wrote:
> On Wed, 2011-07-20 at 12:29 -0700, Paul E. McKenney wrote:
> 
> > Peter, does #4 (protect __rcu_read_unlock() against scheduler-using
> > irq handlers) remove the need for #5 (Add irq_{enter,exit}() to
> > scheduler_ipi()) and #6 (Inform RCU of irq_exit() activity)?  My guess is
> > "no" for #5 and "yes" for #6.
> 
> More or less, we want to keep #5 for it does more than just fix RCU, but
> yeah, I _think_ #4 obsoletes the direct need for #6.

Heh.  So the lowest risk is keeping #6 for now and deciding later
whether we really need it.

							Thanx, Paul
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