linux-kernel - [PATCH tip/core/rcu 1/9] torture: Don't try to offline the last CPU

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Message-Id: <20190326233118.23057-1-paulmck@linux.ibm.com>
Date:   Tue, 26 Mar 2019 16:31:10 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH tip/core/rcu 1/9] torture: Don't try to offline the last CPU

If there is only one online CPU, it doesn't make sense to try to offline
it, as any such attempt is guaranteed to fail.  This commit therefore
check for this condition and refuses to attempt the nonsensical.

Reported-by: Su Yue <suy.fnst@...fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
Tested-By: Su Yue <suy.fnst@...fujitsu.com>
---
 kernel/torture.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/torture.c b/kernel/torture.c
index 8faa1a9aaeb9..17b2be9bde12 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -88,6 +88,8 @@ bool torture_offline(int cpu, long *n_offl_attempts, long *n_offl_successes,
 
 	if (!cpu_online(cpu) || !cpu_is_hotpluggable(cpu))
 		return false;
+	if (num_online_cpus() <= 1)
+		return false;  /* Can't offline the last CPU. */
 
 	if (verbose > 1)
 		pr_alert("%s" TORTURE_FLAG
-- 
2.17.1