Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 25ce9aa4 authored by Pavankumar Kondeti's avatar Pavankumar Kondeti Committed by Gerrit - the friendly Code Review server
Browse files

sched: Fix integer overflow in sched_update_nr_prod() 



"int" type is used to hold the time difference between the successive
updates to nr_run in sched_update_nr_prod(). This can result in
overflow, if the function is called ~2.15 sec after it was called
before. The most probable scenarios are when CPU is idle and
hotplugged. But as we update the last_time of all possible CPUs in
sched_get_nr_running_avg() periodically from a deferrable timer context
(core_ctl module), this overflow is observed only when the system is
completely idle for long time. When this overflow happens we hit
a BUG_ON() in sched_get_nr_running_avg().

Use "u64" type instead of "int" for holding the time difference and
add additional BUG_ON() to catch the instances where sched_clock()
returns a backward value.

Change-Id: I284abb5889ceb8cf9cc689c79ed69422a0e74986
Signed-off-by: default avatarPavankumar Kondeti <pkondeti@codeaurora.org>
parent fbaa89c3

kernel/sched/sched_avg.c

+10 −9
Original line number Diff line number Diff line 
/* Copyright (c) 2012, 2015, The Linux Foundation. All rights reserved.

/* Copyright (c) 2012, 2015-2016, The Linux Foundation. All rights reserved.

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 and
@@ -60,17 +60,17 @@ void sched_get_nr_running_avg(int *avg, int *iowait_avg, int *big_avg) 


		spin_lock_irqsave(&per_cpu(nr_lock, cpu), flags);

		curr_time = sched_clock();

		diff = curr_time - per_cpu(last_time, cpu);

		BUG_ON((s64)diff < 0);



		tmp_avg += per_cpu(nr_prod_sum, cpu);

		tmp_avg += per_cpu(nr, cpu) *

			(curr_time - per_cpu(last_time, cpu));

		tmp_avg += per_cpu(nr, cpu) * diff;



		tmp_big_avg += per_cpu(nr_big_prod_sum, cpu);

		tmp_big_avg += nr_eligible_big_tasks(cpu) *

			(curr_time - per_cpu(last_time, cpu));

		tmp_big_avg += nr_eligible_big_tasks(cpu) * diff;



		tmp_iowait += per_cpu(iowait_prod_sum, cpu);

		tmp_iowait +=  nr_iowait_cpu(cpu) *

			(curr_time - per_cpu(last_time, cpu));

		tmp_iowait +=  nr_iowait_cpu(cpu) * diff;



		per_cpu(last_time, cpu) = curr_time;
@@ -107,14 +107,15 @@ EXPORT_SYMBOL(sched_get_nr_running_avg); 
 */

void sched_update_nr_prod(int cpu, long delta, bool inc)

{

	int diff;

	s64 curr_time;

	u64 diff;

	u64 curr_time;

	unsigned long flags, nr_running;



	spin_lock_irqsave(&per_cpu(nr_lock, cpu), flags);

	nr_running = per_cpu(nr, cpu);

	curr_time = sched_clock();

	diff = curr_time - per_cpu(last_time, cpu);

	BUG_ON((s64)diff < 0);

	per_cpu(last_time, cpu) = curr_time;

	per_cpu(nr, cpu) = nr_running + (inc ? delta : -delta);