Re: [PATCH] sched: reset sysctl_sched_time_avg to default when

[Ethan Zhao]

Peter,


On 2017/9/4 15:32, Peter Zijlstra wrote:

On Sat, Sep 02, 2017 at 08:33:03AM +0800, Ethan Zhao wrote:

Yep, that is the first place I considered to set the limit, but that would
break KABI ?

nah..

  V4 sent, please ignore v2 & v3.

  Thanks,
  Ethan

Re: [PATCH] sched: reset sysctl_sched_time_avg to default when

[Ethan Zhao]

Peter,


On 2017/9/4 15:32, Peter Zijlstra wrote:

On Sat, Sep 02, 2017 at 08:33:03AM +0800, Ethan Zhao wrote:

Yep, that is the first place I considered to set the limit, but that would
break KABI ?

nah..

  V4 sent, please ignore v2 & v3.

  Thanks,
  Ethan

Re: [PATCH] sched: reset sysctl_sched_time_avg to default when

[Peter Zijlstra]

On Sat, Sep 02, 2017 at 08:33:03AM +0800, Ethan Zhao wrote:
> Yep, that is the first place I considered to set the limit, but that would
> break KABI ?

nah..

Re: [PATCH] sched: reset sysctl_sched_time_avg to default when

[Peter Zijlstra]

On Sat, Sep 02, 2017 at 08:33:03AM +0800, Ethan Zhao wrote:
> Yep, that is the first place I considered to set the limit, but that would
> break KABI ?

nah..

Re: [PATCH] sched: reset sysctl_sched_time_avg to default when

[Ethan Zhao]

Peter,

 V2 sent, tested okay on stable 4.1, re-factor a little, could apply
to v4.13-rc5,
please review.

[root@ ~]# sysctl kernel.sched_time_avg_ms
kernel.sched_time_avg_ms = 1000
[root@ ~]# sysctl kernel.sched_time_avg_ms=0
sysctl: setting key "kernel.sched_time_avg_ms": Invalid argument
kernel.sched_time_avg_ms = 0
[root@ ~]# sysctl kernel.sched_time_avg_ms
kernel.sched_time_avg_ms = 1000
[root@ ~]# sysctl kernel.sched_time_avg_ms=900
kernel.sched_time_avg_ms = 900
[root@ ~]# sysctl kernel.sched_time_avg_ms
kernel.sched_time_avg_ms = 900

Thanks,
Ethan

On Sat, Sep 2, 2017 at 8:33 AM, Ethan Zhao  wrote:
> Yep, that is the first place I considered to set the limit, but that would
> break KABI ?
>
> Thanks,
> Ethan
>
> On Fri, Sep 1, 2017 at 8:32 PM, Peter Zijlstra  wrote:
>> On Fri, Sep 01, 2017 at 07:31:54PM +0800, Ethan Zhao wrote:
>>> System will hang if user set sysctl_sched_time_avg to 0 by
>>>
>>> [root@XXX ~]# sysctl kernel.sched_time_avg_ms=0
>>>
>>> Stack traceback for pid 0
>>> 0x883f6406c600 0 0 1 3 R 0x883f6406cf50 *swapper/3
>>> 883f7ccc3ae8 0018 810c4dd0 
>>> 00017800 883f7ccc3d78 0003 883f7ccc3bf8
>>> 810c4fc9 883f7ccc3c08 810c5043 883f7ccc3c08
>>> Call Trace:
>>>  [] ? update_group_capacity+0x110/0x200
>>> [] ? update_sd_lb_stats+0x109/0x600
>>> [] ? find_busiest_group+0x47/0x530
>>> [] ? load_balance+0x194/0x900
>>> [] ? update_rq_clock.part.83+0x1a/0xe0
>>> [] ? rebalance_domains+0x152/0x290
>>> [] ? run_rebalance_domains+0xdc/0x1d0
>>> [] ? __do_softirq+0xfb/0x320
>>> [] ? irq_exit+0x125/0x130
>>> [] ? scheduler_ipi+0x97/0x160
>>> [] ? smp_reschedule_interrupt+0x29/0x30
>>> [] ? reschedule_interrupt+0x6e/0x80
>>>  [] ? cpuidle_enter_state+0xcc/0x230
>>> [] ? cpuidle_enter_state+0x9c/0x230
>>> [] ? cpuidle_enter+0x17/0x20
>>> [] ? cpu_startup_entry+0x38c/0x420
>>> [] ? start_secondary+0x173/0x1e0
>>>
>>> Because divide-by-zero error happens in function
>>>
>>> update_group_capacity()
>>>   update_cpu_capacity()
>>> scale_rt_capacity()
>>>   {
>>>   ...
>>>   total = sched_avg_period() + delta;
>>>   used = div_u64(avg, total);
>>>   ...
>>>   }
>>>
>>> Seems this issue could be reproduced on all I tried stable 4.1 - last
>>> kernel.
>>>
>>> To fix this issue, reset sysctl_sched_time_avg to default value
>>> MSEC_PER_SEC if user input invalid value in function
>>>
>>> sched_avg_period()
>>>
>>> Reported-by: James Puthukattukaran 
>>> Signed-off-by: Ethan Zhao 
>>> ---
>>>  Tested on stable 4.1, compiled on stable 4.13-rc5
>>>  kernel/sched/sched.h | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>>> index eeef1a3..b398560 100644
>>> --- a/kernel/sched/sched.h
>>> +++ b/kernel/sched/sched.h
>>> @@ -1620,6 +1620,9 @@ static inline void rq_last_tick_reset(struct rq *rq)
>>>
>>>  static inline u64 sched_avg_period(void)
>>>  {
>>> + if (unlikely(sysctl_sched_time_avg <= 0))
>>> + sysctl_sched_time_avg = MSEC_PER_SEC;
>>> +
>>
>> Sight, no.. you can set limits in the sysctl table.

Re: [PATCH] sched: reset sysctl_sched_time_avg to default when

[Ethan Zhao]

Peter,

 V2 sent, tested okay on stable 4.1, re-factor a little, could apply
to v4.13-rc5,
please review.

[root@ ~]# sysctl kernel.sched_time_avg_ms
kernel.sched_time_avg_ms = 1000
[root@ ~]# sysctl kernel.sched_time_avg_ms=0
sysctl: setting key "kernel.sched_time_avg_ms": Invalid argument
kernel.sched_time_avg_ms = 0
[root@ ~]# sysctl kernel.sched_time_avg_ms
kernel.sched_time_avg_ms = 1000
[root@ ~]# sysctl kernel.sched_time_avg_ms=900
kernel.sched_time_avg_ms = 900
[root@ ~]# sysctl kernel.sched_time_avg_ms
kernel.sched_time_avg_ms = 900

Thanks,
Ethan

On Sat, Sep 2, 2017 at 8:33 AM, Ethan Zhao  wrote:
> Yep, that is the first place I considered to set the limit, but that would
> break KABI ?
>
> Thanks,
> Ethan
>
> On Fri, Sep 1, 2017 at 8:32 PM, Peter Zijlstra  wrote:
>> On Fri, Sep 01, 2017 at 07:31:54PM +0800, Ethan Zhao wrote:
>>> System will hang if user set sysctl_sched_time_avg to 0 by
>>>
>>> [root@XXX ~]# sysctl kernel.sched_time_avg_ms=0
>>>
>>> Stack traceback for pid 0
>>> 0x883f6406c600 0 0 1 3 R 0x883f6406cf50 *swapper/3
>>> 883f7ccc3ae8 0018 810c4dd0 
>>> 00017800 883f7ccc3d78 0003 883f7ccc3bf8
>>> 810c4fc9 883f7ccc3c08 810c5043 883f7ccc3c08
>>> Call Trace:
>>>  [] ? update_group_capacity+0x110/0x200
>>> [] ? update_sd_lb_stats+0x109/0x600
>>> [] ? find_busiest_group+0x47/0x530
>>> [] ? load_balance+0x194/0x900
>>> [] ? update_rq_clock.part.83+0x1a/0xe0
>>> [] ? rebalance_domains+0x152/0x290
>>> [] ? run_rebalance_domains+0xdc/0x1d0
>>> [] ? __do_softirq+0xfb/0x320
>>> [] ? irq_exit+0x125/0x130
>>> [] ? scheduler_ipi+0x97/0x160
>>> [] ? smp_reschedule_interrupt+0x29/0x30
>>> [] ? reschedule_interrupt+0x6e/0x80
>>>  [] ? cpuidle_enter_state+0xcc/0x230
>>> [] ? cpuidle_enter_state+0x9c/0x230
>>> [] ? cpuidle_enter+0x17/0x20
>>> [] ? cpu_startup_entry+0x38c/0x420
>>> [] ? start_secondary+0x173/0x1e0
>>>
>>> Because divide-by-zero error happens in function
>>>
>>> update_group_capacity()
>>>   update_cpu_capacity()
>>> scale_rt_capacity()
>>>   {
>>>   ...
>>>   total = sched_avg_period() + delta;
>>>   used = div_u64(avg, total);
>>>   ...
>>>   }
>>>
>>> Seems this issue could be reproduced on all I tried stable 4.1 - last
>>> kernel.
>>>
>>> To fix this issue, reset sysctl_sched_time_avg to default value
>>> MSEC_PER_SEC if user input invalid value in function
>>>
>>> sched_avg_period()
>>>
>>> Reported-by: James Puthukattukaran 
>>> Signed-off-by: Ethan Zhao 
>>> ---
>>>  Tested on stable 4.1, compiled on stable 4.13-rc5
>>>  kernel/sched/sched.h | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>>> index eeef1a3..b398560 100644
>>> --- a/kernel/sched/sched.h
>>> +++ b/kernel/sched/sched.h
>>> @@ -1620,6 +1620,9 @@ static inline void rq_last_tick_reset(struct rq *rq)
>>>
>>>  static inline u64 sched_avg_period(void)
>>>  {
>>> + if (unlikely(sysctl_sched_time_avg <= 0))
>>> + sysctl_sched_time_avg = MSEC_PER_SEC;
>>> +
>>
>> Sight, no.. you can set limits in the sysctl table.

Re: [PATCH] sched: reset sysctl_sched_time_avg to default when

[Ethan Zhao]

Yep, that is the first place I considered to set the limit, but that would
break KABI ?

Thanks,
Ethan

On Fri, Sep 1, 2017 at 8:32 PM, Peter Zijlstra  wrote:
> On Fri, Sep 01, 2017 at 07:31:54PM +0800, Ethan Zhao wrote:
>> System will hang if user set sysctl_sched_time_avg to 0 by
>>
>> [root@XXX ~]# sysctl kernel.sched_time_avg_ms=0
>>
>> Stack traceback for pid 0
>> 0x883f6406c600 0 0 1 3 R 0x883f6406cf50 *swapper/3
>> 883f7ccc3ae8 0018 810c4dd0 
>> 00017800 883f7ccc3d78 0003 883f7ccc3bf8
>> 810c4fc9 883f7ccc3c08 810c5043 883f7ccc3c08
>> Call Trace:
>>  [] ? update_group_capacity+0x110/0x200
>> [] ? update_sd_lb_stats+0x109/0x600
>> [] ? find_busiest_group+0x47/0x530
>> [] ? load_balance+0x194/0x900
>> [] ? update_rq_clock.part.83+0x1a/0xe0
>> [] ? rebalance_domains+0x152/0x290
>> [] ? run_rebalance_domains+0xdc/0x1d0
>> [] ? __do_softirq+0xfb/0x320
>> [] ? irq_exit+0x125/0x130
>> [] ? scheduler_ipi+0x97/0x160
>> [] ? smp_reschedule_interrupt+0x29/0x30
>> [] ? reschedule_interrupt+0x6e/0x80
>>  [] ? cpuidle_enter_state+0xcc/0x230
>> [] ? cpuidle_enter_state+0x9c/0x230
>> [] ? cpuidle_enter+0x17/0x20
>> [] ? cpu_startup_entry+0x38c/0x420
>> [] ? start_secondary+0x173/0x1e0
>>
>> Because divide-by-zero error happens in function
>>
>> update_group_capacity()
>>   update_cpu_capacity()
>> scale_rt_capacity()
>>   {
>>   ...
>>   total = sched_avg_period() + delta;
>>   used = div_u64(avg, total);
>>   ...
>>   }
>>
>> Seems this issue could be reproduced on all I tried stable 4.1 - last
>> kernel.
>>
>> To fix this issue, reset sysctl_sched_time_avg to default value
>> MSEC_PER_SEC if user input invalid value in function
>>
>> sched_avg_period()
>>
>> Reported-by: James Puthukattukaran 
>> Signed-off-by: Ethan Zhao 
>> ---
>>  Tested on stable 4.1, compiled on stable 4.13-rc5
>>  kernel/sched/sched.h | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>> index eeef1a3..b398560 100644
>> --- a/kernel/sched/sched.h
>> +++ b/kernel/sched/sched.h
>> @@ -1620,6 +1620,9 @@ static inline void rq_last_tick_reset(struct rq *rq)
>>
>>  static inline u64 sched_avg_period(void)
>>  {
>> + if (unlikely(sysctl_sched_time_avg <= 0))
>> + sysctl_sched_time_avg = MSEC_PER_SEC;
>> +
>
> Sight, no.. you can set limits in the sysctl table.

Re: [PATCH] sched: reset sysctl_sched_time_avg to default when

[Ethan Zhao]

Yep, that is the first place I considered to set the limit, but that would
break KABI ?

Thanks,
Ethan

On Fri, Sep 1, 2017 at 8:32 PM, Peter Zijlstra  wrote:
> On Fri, Sep 01, 2017 at 07:31:54PM +0800, Ethan Zhao wrote:
>> System will hang if user set sysctl_sched_time_avg to 0 by
>>
>> [root@XXX ~]# sysctl kernel.sched_time_avg_ms=0
>>
>> Stack traceback for pid 0
>> 0x883f6406c600 0 0 1 3 R 0x883f6406cf50 *swapper/3
>> 883f7ccc3ae8 0018 810c4dd0 
>> 00017800 883f7ccc3d78 0003 883f7ccc3bf8
>> 810c4fc9 883f7ccc3c08 810c5043 883f7ccc3c08
>> Call Trace:
>>  [] ? update_group_capacity+0x110/0x200
>> [] ? update_sd_lb_stats+0x109/0x600
>> [] ? find_busiest_group+0x47/0x530
>> [] ? load_balance+0x194/0x900
>> [] ? update_rq_clock.part.83+0x1a/0xe0
>> [] ? rebalance_domains+0x152/0x290
>> [] ? run_rebalance_domains+0xdc/0x1d0
>> [] ? __do_softirq+0xfb/0x320
>> [] ? irq_exit+0x125/0x130
>> [] ? scheduler_ipi+0x97/0x160
>> [] ? smp_reschedule_interrupt+0x29/0x30
>> [] ? reschedule_interrupt+0x6e/0x80
>>  [] ? cpuidle_enter_state+0xcc/0x230
>> [] ? cpuidle_enter_state+0x9c/0x230
>> [] ? cpuidle_enter+0x17/0x20
>> [] ? cpu_startup_entry+0x38c/0x420
>> [] ? start_secondary+0x173/0x1e0
>>
>> Because divide-by-zero error happens in function
>>
>> update_group_capacity()
>>   update_cpu_capacity()
>> scale_rt_capacity()
>>   {
>>   ...
>>   total = sched_avg_period() + delta;
>>   used = div_u64(avg, total);
>>   ...
>>   }
>>
>> Seems this issue could be reproduced on all I tried stable 4.1 - last
>> kernel.
>>
>> To fix this issue, reset sysctl_sched_time_avg to default value
>> MSEC_PER_SEC if user input invalid value in function
>>
>> sched_avg_period()
>>
>> Reported-by: James Puthukattukaran 
>> Signed-off-by: Ethan Zhao 
>> ---
>>  Tested on stable 4.1, compiled on stable 4.13-rc5
>>  kernel/sched/sched.h | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>> index eeef1a3..b398560 100644
>> --- a/kernel/sched/sched.h
>> +++ b/kernel/sched/sched.h
>> @@ -1620,6 +1620,9 @@ static inline void rq_last_tick_reset(struct rq *rq)
>>
>>  static inline u64 sched_avg_period(void)
>>  {
>> + if (unlikely(sysctl_sched_time_avg <= 0))
>> + sysctl_sched_time_avg = MSEC_PER_SEC;
>> +
>
> Sight, no.. you can set limits in the sysctl table.

Re: [PATCH] sched: reset sysctl_sched_time_avg to default when

[Peter Zijlstra]

On Fri, Sep 01, 2017 at 07:31:54PM +0800, Ethan Zhao wrote:
> System will hang if user set sysctl_sched_time_avg to 0 by
> 
> [root@XXX ~]# sysctl kernel.sched_time_avg_ms=0
> 
> Stack traceback for pid 0
> 0x883f6406c600 0 0 1 3 R 0x883f6406cf50 *swapper/3
> 883f7ccc3ae8 0018 810c4dd0 
> 00017800 883f7ccc3d78 0003 883f7ccc3bf8
> 810c4fc9 883f7ccc3c08 810c5043 883f7ccc3c08
> Call Trace:
>  [] ? update_group_capacity+0x110/0x200
> [] ? update_sd_lb_stats+0x109/0x600
> [] ? find_busiest_group+0x47/0x530
> [] ? load_balance+0x194/0x900
> [] ? update_rq_clock.part.83+0x1a/0xe0
> [] ? rebalance_domains+0x152/0x290
> [] ? run_rebalance_domains+0xdc/0x1d0
> [] ? __do_softirq+0xfb/0x320
> [] ? irq_exit+0x125/0x130
> [] ? scheduler_ipi+0x97/0x160
> [] ? smp_reschedule_interrupt+0x29/0x30
> [] ? reschedule_interrupt+0x6e/0x80
>  [] ? cpuidle_enter_state+0xcc/0x230
> [] ? cpuidle_enter_state+0x9c/0x230
> [] ? cpuidle_enter+0x17/0x20
> [] ? cpu_startup_entry+0x38c/0x420
> [] ? start_secondary+0x173/0x1e0
> 
> Because divide-by-zero error happens in function
> 
> update_group_capacity()
>   update_cpu_capacity()
> scale_rt_capacity()
>   {
>   ...
>   total = sched_avg_period() + delta;
>   used = div_u64(avg, total);
>   ...
>   }
> 
> Seems this issue could be reproduced on all I tried stable 4.1 - last
> kernel.
> 
> To fix this issue, reset sysctl_sched_time_avg to default value
> MSEC_PER_SEC if user input invalid value in function
> 
> sched_avg_period()
> 
> Reported-by: James Puthukattukaran 
> Signed-off-by: Ethan Zhao 
> ---
>  Tested on stable 4.1, compiled on stable 4.13-rc5 
>  kernel/sched/sched.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index eeef1a3..b398560 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1620,6 +1620,9 @@ static inline void rq_last_tick_reset(struct rq *rq)
>  
>  static inline u64 sched_avg_period(void)
>  {
> + if (unlikely(sysctl_sched_time_avg <= 0))
> + sysctl_sched_time_avg = MSEC_PER_SEC;
> +

Sight, no.. you can set limits in the sysctl table.

Re: [PATCH] sched: reset sysctl_sched_time_avg to default when

[Peter Zijlstra]

On Fri, Sep 01, 2017 at 07:31:54PM +0800, Ethan Zhao wrote:
> System will hang if user set sysctl_sched_time_avg to 0 by
> 
> [root@XXX ~]# sysctl kernel.sched_time_avg_ms=0
> 
> Stack traceback for pid 0
> 0x883f6406c600 0 0 1 3 R 0x883f6406cf50 *swapper/3
> 883f7ccc3ae8 0018 810c4dd0 
> 00017800 883f7ccc3d78 0003 883f7ccc3bf8
> 810c4fc9 883f7ccc3c08 810c5043 883f7ccc3c08
> Call Trace:
>  [] ? update_group_capacity+0x110/0x200
> [] ? update_sd_lb_stats+0x109/0x600
> [] ? find_busiest_group+0x47/0x530
> [] ? load_balance+0x194/0x900
> [] ? update_rq_clock.part.83+0x1a/0xe0
> [] ? rebalance_domains+0x152/0x290
> [] ? run_rebalance_domains+0xdc/0x1d0
> [] ? __do_softirq+0xfb/0x320
> [] ? irq_exit+0x125/0x130
> [] ? scheduler_ipi+0x97/0x160
> [] ? smp_reschedule_interrupt+0x29/0x30
> [] ? reschedule_interrupt+0x6e/0x80
>  [] ? cpuidle_enter_state+0xcc/0x230
> [] ? cpuidle_enter_state+0x9c/0x230
> [] ? cpuidle_enter+0x17/0x20
> [] ? cpu_startup_entry+0x38c/0x420
> [] ? start_secondary+0x173/0x1e0
> 
> Because divide-by-zero error happens in function
> 
> update_group_capacity()
>   update_cpu_capacity()
> scale_rt_capacity()
>   {
>   ...
>   total = sched_avg_period() + delta;
>   used = div_u64(avg, total);
>   ...
>   }
> 
> Seems this issue could be reproduced on all I tried stable 4.1 - last
> kernel.
> 
> To fix this issue, reset sysctl_sched_time_avg to default value
> MSEC_PER_SEC if user input invalid value in function
> 
> sched_avg_period()
> 
> Reported-by: James Puthukattukaran 
> Signed-off-by: Ethan Zhao 
> ---
>  Tested on stable 4.1, compiled on stable 4.13-rc5 
>  kernel/sched/sched.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index eeef1a3..b398560 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1620,6 +1620,9 @@ static inline void rq_last_tick_reset(struct rq *rq)
>  
>  static inline u64 sched_avg_period(void)
>  {
> + if (unlikely(sysctl_sched_time_avg <= 0))
> + sysctl_sched_time_avg = MSEC_PER_SEC;
> +

Sight, no.. you can set limits in the sysctl table.

[PATCH] sched: reset sysctl_sched_time_avg to default when

[Ethan Zhao]

System will hang if user set sysctl_sched_time_avg to 0 by

[root@XXX ~]# sysctl kernel.sched_time_avg_ms=0

Stack traceback for pid 0
0x883f6406c600 0 0 1 3 R 0x883f6406cf50 *swapper/3
883f7ccc3ae8 0018 810c4dd0 
00017800 883f7ccc3d78 0003 883f7ccc3bf8
810c4fc9 883f7ccc3c08 810c5043 883f7ccc3c08
Call Trace:
 [] ? update_group_capacity+0x110/0x200
[] ? update_sd_lb_stats+0x109/0x600
[] ? find_busiest_group+0x47/0x530
[] ? load_balance+0x194/0x900
[] ? update_rq_clock.part.83+0x1a/0xe0
[] ? rebalance_domains+0x152/0x290
[] ? run_rebalance_domains+0xdc/0x1d0
[] ? __do_softirq+0xfb/0x320
[] ? irq_exit+0x125/0x130
[] ? scheduler_ipi+0x97/0x160
[] ? smp_reschedule_interrupt+0x29/0x30
[] ? reschedule_interrupt+0x6e/0x80
 [] ? cpuidle_enter_state+0xcc/0x230
[] ? cpuidle_enter_state+0x9c/0x230
[] ? cpuidle_enter+0x17/0x20
[] ? cpu_startup_entry+0x38c/0x420
[] ? start_secondary+0x173/0x1e0

Because divide-by-zero error happens in function

update_group_capacity()
  update_cpu_capacity()
scale_rt_capacity()
{
...
total = sched_avg_period() + delta;
used = div_u64(avg, total);
...
}

Seems this issue could be reproduced on all I tried stable 4.1 - last
kernel.

To fix this issue, reset sysctl_sched_time_avg to default value
MSEC_PER_SEC if user input invalid value in function

sched_avg_period()

Reported-by: James Puthukattukaran 
Signed-off-by: Ethan Zhao 
---
 Tested on stable 4.1, compiled on stable 4.13-rc5 
 kernel/sched/sched.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index eeef1a3..b398560 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1620,6 +1620,9 @@ static inline void rq_last_tick_reset(struct rq *rq)
 
 static inline u64 sched_avg_period(void)
 {
+   if (unlikely(sysctl_sched_time_avg <= 0))
+   sysctl_sched_time_avg = MSEC_PER_SEC;
+
return (u64)sysctl_sched_time_avg * NSEC_PER_MSEC / 2;
 }
 
-- 
1.8.3.1

[PATCH] sched: reset sysctl_sched_time_avg to default when

[Ethan Zhao]

System will hang if user set sysctl_sched_time_avg to 0 by

[root@XXX ~]# sysctl kernel.sched_time_avg_ms=0

Stack traceback for pid 0
0x883f6406c600 0 0 1 3 R 0x883f6406cf50 *swapper/3
883f7ccc3ae8 0018 810c4dd0 
00017800 883f7ccc3d78 0003 883f7ccc3bf8
810c4fc9 883f7ccc3c08 810c5043 883f7ccc3c08
Call Trace:
 [] ? update_group_capacity+0x110/0x200
[] ? update_sd_lb_stats+0x109/0x600
[] ? find_busiest_group+0x47/0x530
[] ? load_balance+0x194/0x900
[] ? update_rq_clock.part.83+0x1a/0xe0
[] ? rebalance_domains+0x152/0x290
[] ? run_rebalance_domains+0xdc/0x1d0
[] ? __do_softirq+0xfb/0x320
[] ? irq_exit+0x125/0x130
[] ? scheduler_ipi+0x97/0x160
[] ? smp_reschedule_interrupt+0x29/0x30
[] ? reschedule_interrupt+0x6e/0x80
 [] ? cpuidle_enter_state+0xcc/0x230
[] ? cpuidle_enter_state+0x9c/0x230
[] ? cpuidle_enter+0x17/0x20
[] ? cpu_startup_entry+0x38c/0x420
[] ? start_secondary+0x173/0x1e0

Because divide-by-zero error happens in function

update_group_capacity()
  update_cpu_capacity()
scale_rt_capacity()
{
...
total = sched_avg_period() + delta;
used = div_u64(avg, total);
...
}

Seems this issue could be reproduced on all I tried stable 4.1 - last
kernel.

To fix this issue, reset sysctl_sched_time_avg to default value
MSEC_PER_SEC if user input invalid value in function

sched_avg_period()

Reported-by: James Puthukattukaran 
Signed-off-by: Ethan Zhao 
---
 Tested on stable 4.1, compiled on stable 4.13-rc5 
 kernel/sched/sched.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index eeef1a3..b398560 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1620,6 +1620,9 @@ static inline void rq_last_tick_reset(struct rq *rq)
 
 static inline u64 sched_avg_period(void)
 {
+   if (unlikely(sysctl_sched_time_avg <= 0))
+   sysctl_sched_time_avg = MSEC_PER_SEC;
+
return (u64)sysctl_sched_time_avg * NSEC_PER_MSEC / 2;
 }
 
-- 
1.8.3.1