linux-kernel - Re: [PATCH] rcu: declare rcu_data variables in the section they are defined in

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Message-ID: <20150504203325.GE5381@linux.vnet.ibm.com>
Date:	Mon, 4 May 2015 13:33:26 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Nicolas Iooss <nicolas.iooss_linux@....org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu: declare rcu_data variables in the section they are
 defined in

On Sun, May 03, 2015 at 12:27:02PM -0700, Josh Triplett wrote:
> On Sun, May 03, 2015 at 05:57:53PM +0800, Nicolas Iooss wrote:
> > Commit 11bbb235c26f ("rcu: Use DEFINE_PER_CPU_SHARED_ALIGNED for
> > rcu_data") replaced DEFINE_PER_CPU by DEFINE_PER_CPU_SHARED_ALIGNED in
> > the definition of rcu_sched and rcu_bh without updating
> > kernel/rcu/tree.h.
> > 
> > This makes clang report a section mismatch (-Wsection warning) when
> > building LLVMLinux because the variables are declared in .data..percpu
> > but defined in .data..percpu..shared_aligned.
> > 
> > Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@....org>
> 
> Good catch.
> Reviewed-by: Josh Triplett <josh@...htriplett.org>

Agreed, good catch!  But don't we also need to worry about
rcu_preempt_data?  Also, given that tree_trace.c now uses iterators
rather than direct access via the per-CPU variables, wouldn't the
following be more appropriate?  (-Very- lightly tested.)

							Thanx, Paul

------------------------------------------------------------------------

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index da9f6adb5ff9..ee86870b1825 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -537,17 +537,6 @@ extern struct list_head rcu_struct_flavors;
 /*
  * RCU implementation internal declarations:
  */
-extern struct rcu_state rcu_sched_state;
-DECLARE_PER_CPU(struct rcu_data, rcu_sched_data);
-
-extern struct rcu_state rcu_bh_state;
-DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
-
-#ifdef CONFIG_PREEMPT_RCU
-extern struct rcu_state rcu_preempt_state;
-DECLARE_PER_CPU(struct rcu_data, rcu_preempt_data);
-#endif /* #ifdef CONFIG_PREEMPT_RCU */
-
 #ifdef CONFIG_RCU_BOOST
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
 DECLARE_PER_CPU(int, rcu_cpu_kthread_cpu);

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