From 7400d3bbaa229eb8e7631d28fb34afd7cd2c96ff Mon Sep 17 00:00:00 2001
From: Byungchul Park <byungchul.park@lge.com>
Date: Fri, 15 Jan 2016 16:07:49 +0900
Subject: [PATCH] sched/fair: Avoid using decay_load_missed() with a negative
value
decay_load_missed() cannot handle nagative values, so we need to prevent
using the function with a negative value.
Reported-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
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: Thomas Gleixner <tglx@linutronix.de>
Cc: perterz@infradead.org
Fixes: 59543275488d ("sched/fair: Prepare __update_cpu_load() to handle active tickless")
Link: http://lkml.kernel.org/r/20160115070749.GA1914@X58A-UD3R
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/fair.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5641042274988..3b3dc39671f84 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4509,9 +4509,17 @@ static void __update_cpu_load(struct rq *this_rq, unsigned long this_load,
/* scale is effectively 1 << i now, and >> i divides by scale */
- old_load = this_rq->cpu_load[i] - tickless_load;
+ old_load = this_rq->cpu_load[i];
old_load = decay_load_missed(old_load, pending_updates - 1, i);
- old_load += tickless_load;
+ if (tickless_load) {
+ old_load -= decay_load_missed(tickless_load, pending_updates - 1, i);
+ /*
+ * old_load can never be a negative value because a
+ * decayed tickless_load cannot be greater than the
+ * original tickless_load.
+ */
+ old_load += tickless_load;
+ }
new_load = this_load;
/*
* Round up the averaging division if load is increasing. This
--
2.39.5