sched/fair: Avoid newidle balance for !active CPUs

Peter Zijlstra · ingomolnar · commit 2800486ee348 · 2017-09-12T17:41:03.000+02:00
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: 77d1dfd ("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: 77d1dfd ("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
@@ -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
