linux-kernel - [RFC rcu/next] torture: Stop onoff task if there is only one cpu

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Date:	Mon,  2 May 2016 10:30:00 +0800
From:	Boqun Feng <boqun.feng@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>
Subject: [RFC rcu/next] torture: Stop onoff task if there is only one cpu

If the whole system has only one cpu, that cpu won't be able to be
offlined, so there is no need onoff task is stil running.

Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---

I hit something like the following while I was running rcutorture
in a guest with only one vCPU:

[   31.197457] rcu-torture:torture_onoff task: offlining 0
[   31.197508] rcu-torture:torture_onoff task: offline 0 failed: errno -16

I know this is an expected behavior, but think we could just stop
the onoff task if there is only one cpu.

 kernel/torture.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/torture.c b/kernel/torture.c
index fb39a06bbef5..a85b7d61d9dd 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -194,6 +194,12 @@ torture_onoff(void *arg)
 	for_each_online_cpu(cpu)
 		maxcpu = cpu;
 	WARN_ON(maxcpu < 0);
+
+	if (maxcpu == 0) {
+		VERBOSE_TOROUT_STRING("only one cpu is found, onoff is impossible");
+		goto stop;
+	}
+
 	if (onoff_holdoff > 0) {
 		VERBOSE_TOROUT_STRING("torture_onoff begin holdoff");
 		schedule_timeout_interruptible(onoff_holdoff);
@@ -209,6 +215,8 @@ torture_onoff(void *arg)
 				       &sum_online, &min_online, &max_online);
 		schedule_timeout_interruptible(onoff_interval);
 	}
+
+stop:
 	torture_kthread_stopping("torture_onoff");
 	return 0;
 }
-- 
2.8.0