Commit 7400d3bb authored Jan 15, 2016 by Byungchul Park Committed by Ingo Molnar Feb 29, 2016

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: 59543275 ("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>

parent 6aa447bc

kernel/sched/fair.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -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);
		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

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