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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: Pavankumar Kondeti <pkondeti@codeaurora.org>
This commit is contained in:
Pavankumar Kondeti 2016-09-28 12:21:03 +05:30 committed by Gerrit - the friendly Code Review server
parent 9ae0217aa6
commit e593048d81
1 changed files with 10 additions and 9 deletions
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19
kernel/sched/sched_avg.c
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@ -1,4 +1,4 @@
/* 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);