linux-kernel - [PATCH tip/core/rcu 06/22] rcu: Move _rcu_barrier()'s rcu_head structures to rcu

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Date:	Fri, 22 Jun 2012 08:17:05 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, 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, sbw@....edu, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 06/22] rcu: Move _rcu_barrier()'s rcu_head structures to rcu_data structures

From: "Paul E. McKenney" <paul.mckenney@...aro.org>

In order for multiple flavors of RCU to each concurrently run one
rcu_barrier(), each flavor needs its own per-CPU set of rcu_head
structures.  This commit therefore moves _rcu_barrier()'s set of
per-CPU rcu_head structures from per-CPU variables to the existing
per-CPU and per-RCU-flavor rcu_data structures.

Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@...htriplett.org>
---
 kernel/rcutree.c |    6 ++----
 kernel/rcutree.h |    3 +++
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 24cd2f0..cb2d35d 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -157,7 +157,6 @@ unsigned long rcutorture_vernum;
 
 /* State information for rcu_barrier() and friends. */
 
-static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
 static atomic_t rcu_barrier_cpu_count;
 static DEFINE_MUTEX(rcu_barrier_mutex);
 static struct completion rcu_barrier_completion;
@@ -2279,12 +2278,11 @@ static void rcu_barrier_callback(struct rcu_head *notused)
  */
 static void rcu_barrier_func(void *type)
 {
-	int cpu = smp_processor_id();
-	struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
 	struct rcu_state *rsp = type;
+	struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
 
 	atomic_inc(&rcu_barrier_cpu_count);
-	rsp->call(head, rcu_barrier_callback);
+	rsp->call(&rdp->barrier_head, rcu_barrier_callback);
 }
 
 /*
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 15837d7..1783eae 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -300,6 +300,9 @@ struct rcu_data {
 	unsigned long n_rp_need_fqs;
 	unsigned long n_rp_need_nothing;
 
+	/* 6) _rcu_barrier() callback. */
+	struct rcu_head barrier_head;
+
 	int cpu;
 	struct rcu_state *rsp;
 };
-- 
1.7.8

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