From: Chris Redpath <chris.redpath@arm.com>
Date: Wed, 11 Jun 2014 13:08:40 +0000 (+0100)
Subject: sched: hmp: fix out-of-range CPU possible
X-Git-Tag: firefly_0821_release~3680^2~16^2^2~4
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=4378062f289e67259f017f6b176ee385dc974836;p=firefly-linux-kernel-4.4.55.git

sched: hmp: fix out-of-range CPU possible

If someone hotplugs all the little CPUs while another CPU is handling
a wakeup, we can potentially return new_cpu == NR_CPUS from
hmp_select_slower_cpu (which is called internally by
hmp_best_little_cpu as well). We will use this to deref the
per_cpu rq array in hmp_next_down_delay which can go boom.

Signed-off-by: Chris Redpath <chris.redpath@arm.com>
Signed-off-by: Jon Medhurst <tixy@linaro.org>
---

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ffa643ce9116..26c43b463017 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4456,7 +4456,11 @@ unlock:
 #else
 		new_cpu = hmp_select_slower_cpu(p, prev_cpu);
 #endif
-		if (new_cpu != prev_cpu) {
+		/*
+		 * we might have no suitable CPU
+		 * in which case new_cpu == NR_CPUS
+		 */
+		if (new_cpu < NR_CPUS && new_cpu != prev_cpu) {
 			hmp_next_down_delay(&p->se, new_cpu);
 			trace_sched_hmp_migrate(p, new_cpu, HMP_MIGRATE_WAKEUP);
 			return new_cpu;