linux-kernel - [PATCH tip/core/rcu 22/22] rcu: Prevent offline CPUs from executing RCU core code

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Message-Id: <1340378241-6458-22-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Fri, 22 Jun 2012 08:17:21 -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 22/22] rcu: Prevent offline CPUs from executing RCU core code

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

Earlier versions of RCU invoked the RCU core from the CPU_DYING notifier
in order to note a quiescent state for the outgoing CPU.  Because the
CPU is marked "offline" during the execution of the CPU_DYING notifiers,
the RCU core had to tolerate being invoked from an offline CPU.  However,
commit b1420f1c (Make rcu_barrier() less disruptive) left only tracing
code in the CPU_DYING notifier, so the RCU core need no longer execute
on offline CPUs.  This commit therefore enforces this restriction.

Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcutree.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d21c2d3..cbf4d05 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1880,6 +1880,8 @@ static void rcu_process_callbacks(struct softirq_action *unused)
 {
 	struct rcu_state *rsp;
 
+	if (cpu_is_offline(smp_processor_id()))
+		return;
 	trace_rcu_utilization("Start RCU core");
 	for_each_rcu_flavor(rsp)
 		__rcu_process_callbacks(rsp);
-- 
1.7.8

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