sched/fair: Avoid newidle balance for !active CPUs

On CPU hot unplug, when parking the last kthread we'll try and
schedule into idle to kill the CPU. This last schedule can (and does)
trigger newidle balance because at this point the sched domains are
still up because of commit:

  77d1dfda0e79 ("sched/topology, cpuset: Avoid spurious/wrong domain rebuilds")

Obviously pulling tasks to an already offline CPU is a bad idea, and
all balancing operations _should_ be subject to cpu_active_mask, make
it so.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Fixes: 77d1dfda0e79 ("sched/topology, cpuset: Avoid spurious/wrong domain rebuilds")
Link: http://lkml.kernel.org/r/20170907150613.994135806@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8415d1ec2b841e04c5270816d6e116b0f3d0277a..3bcea40d3029627f06831924c5873843fc2e2362 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8447,6 +8447,12 @@ static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
         */
        this_rq->idle_stamp = rq_clock(this_rq);
 
+       /*
+        * Do not pull tasks towards !active CPUs...
+        */
+       if (!cpu_active(this_cpu))
+               return 0;
+
        /*
         * This is OK, because current is on_cpu, which avoids it being picked
         * for load-balance and preemption/IRQs are still disabled avoiding