linux-kernel - Re: [PATCH RFC tip/core/rcu 28/28] rcu: Fix idle-task checks

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Message-ID: <20111103045509.GH2042@leaf>
Date:	Wed, 2 Nov 2011 21:55:09 -0700
From:	Josh Triplett <josh@...htriplett.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, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	patches@...aro.org, "Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH RFC tip/core/rcu 28/28] rcu: Fix idle-task checks

On Wed, Nov 02, 2011 at 01:30:49PM -0700, Paul E. McKenney wrote:
> From: Paul E. McKenney <paul.mckenney@...aro.org>
> 
> RCU has traditionally relied on idle_cpu() to determine whether a given
> CPU is running in the context of an idle task, but recent changes have
> invalidated this approach.  This commit therefore switches from idle_cpu
> to "current->pid != 0".

Could you elaborate a bit on "recent changes"?  It looks like you mean
commit 908a3283728d92df36e0c7cd63304fd35e93a8a9; if so, could you add
that reference to the commit message?

Also, the hard-coded use of "current->pid != 0" concerns me.  Could this
use some existing function?  Does idle_task() help?  If no appropriate
predicate exists, perhaps it should.  is_idle_task(current)?

- Josh Triplett
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