linux-kernel - [PATCH 3/3] sched: don't scan all-offline ->cpus_allowed twice if !CONFIG

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Date:	Sat, 10 Oct 2015 20:53:15 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	heiko.carstens@...ibm.com, Tejun Heo <tj@...nel.org>,
	Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vitaly Kuznetsov <vkuznets@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] sched: don't scan all-offline ->cpus_allowed twice if
	!CONFIG_CPUSETS

If CONFIG_CPUSETS=n then "case cpuset" changes the state and runs
the already failed for_each_cpu() loop again for no reason.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/sched/core.c |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e4fa6be..b421e24 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1335,13 +1335,15 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 			goto out;
 		}
 
+		/* No more Mr. Nice Guy. */
 		switch (state) {
 		case cpuset:
-			/* No more Mr. Nice Guy. */
-			cpuset_cpus_allowed_fallback(p);
-			state = possible;
-			break;
-
+			if (IS_ENABLED(CONFIG_CPUSETS)) {
+				cpuset_cpus_allowed_fallback(p);
+				state = possible;
+				break;
+			}
+			/* fall-through */
 		case possible:
 			do_set_cpus_allowed(p, cpu_possible_mask);
 			state = fail;
-- 
1.5.5.1

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