linux-kernel - [tip:sched/core] sched/fair: Avoid using decay_load

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Message-ID: <tip-7400d3bbaa229eb8e7631d28fb34afd7cd2c96ff@git.kernel.org>
Date:	Mon, 29 Feb 2016 03:14:29 -0800
From:	tip-bot for Byungchul Park <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	cl@...ux.com, fweisbec@...il.com, efault@....de,
	paulmck@...ux.vnet.ibm.com, peterz@...radead.org,
	tglx@...utronix.de, torvalds@...ux-foundation.org, riel@...hat.com,
	lcapitulino@...hat.com, byungchul.park@....com, mingo@...nel.org,
	cmetcalf@...hip.com, linux-kernel@...r.kernel.org,
	dietmar.eggemann@....com, hpa@...or.com
Subject: [tip:sched/core] sched/fair: Avoid using decay_load_missed() with a
 negative value

Commit-ID:  7400d3bbaa229eb8e7631d28fb34afd7cd2c96ff
Gitweb:     http://git.kernel.org/tip/7400d3bbaa229eb8e7631d28fb34afd7cd2c96ff
Author:     Byungchul Park <byungchul.park@....com>
AuthorDate: Fri, 15 Jan 2016 16:07:49 +0900
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 29 Feb 2016 09:53:03 +0100

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@....com>
Signed-off-by: Byungchul Park <byungchul.park@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Chris Metcalf <cmetcalf@...hip.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@...hat.com>
Cc: Mike Galbraith <efault@....de>
Cc: Paul E . McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: perterz@...radead.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@...nel.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 5641042..3b3dc39 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