[PATCH] rcu: more careful check for the last non-dyntick-idle CPU

[Lai Jiangshan <laijs@cn.fujitsu.com>]

Warning: I just did build test.

Subject: [PATCH] rcu: more careful check for the last non-dyntick-idle CPU

If a CPU is not in nohz_cpu_mask, it does not means this
CPU is a non-dyntick-idle CPU, because this CPU may be offline or not exist.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 4befb64..6086a7d 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1026,7 +1026,7 @@ int rcu_needs_cpu(int cpu)
 
 	/* Don't bother unless we are the last non-dyntick-idle CPU. */
 	for_each_cpu_not(thatcpu, nohz_cpu_mask)
-		if (thatcpu != cpu) {
+		if (cpu_online(thatcpu) && thatcpu != cpu) {
 			per_cpu(rcu_dyntick_drain, cpu) = 0;
 			per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
 			return rcu_needs_cpu_quick_check(cpu);