rcu: Prevent offline CPUs from executing RCU core code

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>

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 300aba6926928dc75f80102e16ceab5e7c4d02ee..84a6f55fa1456203aca91c6887300e138eb1fc64 100644 (file)
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1892,6 +1892,8 @@ 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);