[Devel] [PATCH v2 vz8] kernel/sched/fair.c: Add missing update_rq_clock() calls

[Andrey Ryabinin]

On 9/29/20 11:24 AM, Kirill Tkhai wrote:
> On 28.09.2020 15:03, Andrey Ryabinin wrote:
>> We've got a hard lockup which seems to be caused by mgag200
>> console printk code calling to schedule_work from scheduler
>> with rq->lock held:
>>   #5 [ffffb79e034239a8] native_queued_spin_lock_slowpath at ffffffff8b50c6c6
>>   #6 [ffffb79e034239a8] _raw_spin_lock at ffffffff8bc96e5c
>>   #7 [ffffb79e034239b0] try_to_wake_up at ffffffff8b4e26ff
>>   #8 [ffffb79e03423a10] __queue_work at ffffffff8b4ce3f3
>>   #9 [ffffb79e03423a58] queue_work_on at ffffffff8b4ce714
>>  #10 [ffffb79e03423a68] mga_imageblit at ffffffffc026d666 [mgag200]
>>  #11 [ffffb79e03423a80] soft_cursor at ffffffff8b8a9d84
>>  #12 [ffffb79e03423ad8] bit_cursor at ffffffff8b8a99b2
>>  #13 [ffffb79e03423ba0] hide_cursor at ffffffff8b93bc7a
>>  #14 [ffffb79e03423bb0] vt_console_print at ffffffff8b93e07d
>>  #15 [ffffb79e03423c18] console_unlock at ffffffff8b518f0e
>>  #16 [ffffb79e03423c68] vprintk_emit_log at ffffffff8b51acf7
>>  #17 [ffffb79e03423cc0] vprintk_default at ffffffff8b51adcd
>>  #18 [ffffb79e03423cd0] printk at ffffffff8b51b3d6
>>  #19 [ffffb79e03423d30] __warn_printk at ffffffff8b4b13a0
>>  #20 [ffffb79e03423d98] assert_clock_updated at ffffffff8b4dd293
>>  #21 [ffffb79e03423da0] deactivate_task at ffffffff8b4e12d1
>>  #22 [ffffb79e03423dc8] move_task_group at ffffffff8b4eaa5b
>>  #23 [ffffb79e03423e00] cpulimit_balance_cpu_stop at ffffffff8b4f02f3
>>  #24 [ffffb79e03423eb0] cpu_stopper_thread at ffffffff8b576b67
>>  #25 [ffffb79e03423ee8] smpboot_thread_fn at ffffffff8b4d9125
>>  #26 [ffffb79e03423f10] kthread at ffffffff8b4d4fc2
>>  #27 [ffffb79e03423f50] ret_from_fork at ffffffff8be00255
>>
>> The printk called because assert_clock_updated() triggered
>> 	SCHED_WARN_ON(rq->clock_update_flags < RQCF_ACT_SKIP);
>>
>> This means that we missing necessary update_rq_clock() call.
>> Add one to cpulimit_balance_cpu_stop() to fix the warning.
>> Also add one in load_balance() before move_task_groups() call.
>> It seems to be another place missing this call.
>>
>> https://jira.sw.ru/browse/PSBM-108013
>> Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
>> ---
>>  kernel/sched/fair.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 5d3556b15e70..e6dc21d5fa03 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -7816,6 +7816,7 @@ static int cpulimit_balance_cpu_stop(void *data)
>>  
>>  		schedstat_inc(sd->clb_count);
>>  
>> +		update_rq_clock(rq);
> 
> Shouldn't we also add the same for target_rq to avoid WARN() coming from attach_task()?
> 

It seems like we should.