linux-kernel - Re: [PATCH tip/core/rcu 14/14] rcu: Fix rcu_is_cpu_idle() #ifdef in TINY

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Date:	Fri, 15 Jun 2012 16:05:07 -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,
	fweisbec@...il.com, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 14/14] rcu: Fix rcu_is_cpu_idle() #ifdef in
 TINY_RCU

On Fri, Jun 15, 2012 at 03:57:49PM -0700, Paul E. McKenney wrote:
> On Fri, Jun 15, 2012 at 02:28:28PM -0700, Josh Triplett wrote:
> > On Fri, Jun 15, 2012 at 01:13:15PM -0700, Paul E. McKenney wrote:
> > > From: "Paul E. McKenney" <paul.mckenney@...aro.org>
> > > 
> > > The rcu_is_cpu_idle() function is used if CONFIG_DEBUG_LOCK_ALLOC,
> > > but TINY_RCU defines it only when CONFIG_PROVE_RCU.  This causes
> > > build failures when CONFIG_DEBUG_LOCK_ALLOC=y but CONFIG_PROVE_RCU=n.
> > > This commit therefore adjusts the #ifdefs for rcu_is_cpu_idle() so
> > > that it is defined when CONFIG_DEBUG_LOCK_ALLOC=y.
> > > 
> > > Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > 
> > Given that an earlier patch in this series makes rcupdate.h
> > unconditionally prototype rcu_is_cpu_idle, shouldn't rcutiny.c define it
> > unconditionally?  (And do so before the earlier patch in this series
> > makes it available unconditionally?)
> 
> Or update that earlier patch so that it keeps rcu_is_cpu_idle() under
> #ifdef CONFIG_DEBUG_LOCK_ALLOC.  Either way, good catch!
> 
> Hmmm...  I want it under CONFIG_DEBUG_LOCK_ALLOC for TINY_RCU (memory
> footprint and all that), but unconditional for TREE_RCU.  That can
> be arranged...

Seems reasonable to me, as long as the availability of the prototype at
compile time always matches the availability of the function at link
time.

- Josh Triplett
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