Re: Potential problem with 31e77c93e432dec7 ("sched/fair: Update blocked load when newly idle")

[Vincent Guittot]

On 13 April 2018 at 22:38, Niklas SÃderlund
<niklas.soderlund@xxxxxxxxxxxx> wrote:
> Hi Vincent,
>
> On 2018-04-12 13:15:19 +0200, Niklas SÃderlund wrote:
>> Hi Vincent,
>>
>> Thanks for your feedback.
>>
>> On 2018-04-12 12:33:27 +0200, Vincent Guittot wrote:
>> > Hi Niklas,
>> >
>> > On 12 April 2018 at 11:18, Niklas SÃderlund
>> > <niklas.soderlund@xxxxxxxxxxxx> wrote:
>> > > Hi Vincent,
>> > >
>> > > I have observed issues running on linus/master from a few days back [1].
>> > > I'm running on a Renesas Koelsch board (arm32) and I can trigger a issue
>> > > by X forwarding the v4l2 test application qv4l2 over ssh and moving the
>> > > courser around in the GUI (best test case description award...). I'm
>> > > sorry about the really bad way I trigger this but I can't do it in any
>> > > other way, I'm happy to try other methods if you got some ideas. The
>> > > symptom of the issue is a complete hang of the system for more then 30
>> > > seconds and then this information is printed in the console:
>> >
>> > Heiner (edded cc) also reported similar problem with his platform: a
>> > dual core celeron
>> >
>> > Do you confirm that your platform is a dual cortex-A15 ? At least that
>> > what I have seen on web
>> > This would confirm that dual system is a key point.
>>
>> I can confirm that my platform is a dual core.
>
> I tested another dual core system today Renesas M3-W ARM64 system and I
> can observe the same lockups-on that system if it helps you understand
> the problem. It seems to be much harder to trigger the issue on this
> system for some reason. Hitting return in a ssh session don't seem to
> produce the lockup while starting a GUI using X forwarding over ssh it's
> possible.

Thanks for the test. That's confirm, it's only happen on dual core

>
> [  392.306441] INFO: rcu_preempt detected stalls on CPUs/tasks:
> [  392.312201]  (detected by 0, t=19366 jiffies, g=7177, c=7176, q=35)
> [  392.318555] All QSes seen, last rcu_preempt kthread activity 19368
> (4294990375-4294971007), jiffies_till_next_fqs=1, root ->qsmask 0x0
> [  392.330758] swapper/0       R  running task        0     0      0
> 0x00000022
> [  392.337883] Call trace:
> [  392.340365]  dump_backtrace+0x0/0x1c8
> [  392.344065]  show_stack+0x14/0x20
> [  392.347416]  sched_show_task+0x224/0x2e8
> [  392.351377]  rcu_check_callbacks+0x8ac/0x8b0
> [  392.355686]  update_process_times+0x2c/0x58
> [  392.359908]  tick_sched_handle.isra.5+0x30/0x50
> [  392.364479]  tick_sched_timer+0x40/0x90
> [  392.368351]  __hrtimer_run_queues+0xfc/0x208
> [  392.372659]  hrtimer_interrupt+0xd4/0x258
> [  392.376710]  arch_timer_handler_virt+0x28/0x48
> [  392.381194]  handle_percpu_devid_irq+0x80/0x138
> [  392.385767]  generic_handle_irq+0x28/0x40
> [  392.389813]  __handle_domain_irq+0x5c/0xb8
> [  392.393946]  gic_handle_irq+0x58/0xa8
> [  392.397640]  el1_irq+0xb4/0x130
> [  392.400810]  arch_cpu_idle+0x14/0x20
> [  392.404422]  default_idle_call+0x1c/0x38
> [  392.408381]  do_idle+0x17c/0x1f8
> [  392.411640]  cpu_startup_entry+0x20/0x28
> [  392.415598]  rest_init+0x24c/0x260
> [  392.419037]  start_kernel+0x3e8/0x414
>
> I was running the same tests on another ARM64 platform earlier using the
> same build which have more then two cores and there I could not observe
> this issue.
>
> --
> Regards,
> Niklas SÃderlund