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

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

From: "Paul E. McKenney" <paul.mckenney@linaro.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@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.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