[tip:sched/core] sched: Don't scan all-offline -> cpus_allowed twice if !CONFIG_CPUSETS

[tip-bot for Oleg Nesterov <tipbot@zytor.com>]

Commit-ID:  e73e85f0593832aa583b252f9a16cf90ed6d30fa
Gitweb:     http://git.kernel.org/tip/e73e85f0593832aa583b252f9a16cf90ed6d30fa
Author:     Oleg Nesterov <oleg@redhat.com>
AuthorDate: Sat, 10 Oct 2015 20:53:15 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 20 Oct 2015 10:25:57 +0200

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@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: heiko.carstens@de.ibm.com
Link: http://lkml.kernel.org/r/20151010185315.GA24100@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/core.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a7b368e..b4d263d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1580,13 +1580,15 @@ 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;