Re: rcu_preempt self-detected stall on CPU from 4.5-rc3, since 3.17

[Mathieu Desnoyers]

----- On Mar 25, 2016, at 5:46 PM, Paul E. McKenney paulmck@xxxxxxxxxxxxxxxxxx wrote:

> On Fri, Mar 25, 2016 at 09:24:14PM +0000, Chatre, Reinette wrote:
>> Hi  Paul,
>> 
>> On 2016-03-23, Paul E. McKenney wrote:
>> > Please boot with the following parameters:
>> > 
>> > 	rcu_tree.rcu_kick_kthreads ftrace
>> > trace_event=sched_waking,sched_wakeup,sched_wake_idle_without_ipi
>> 
>> With these parameters I expected more details to show up in the kernel logs but
>> cannot find any. Even so, today I left the machine running again and when this
>> happened I think I was able to capture the trace data for the event. Please
>> find attached the trace information for the kernel message below. Since the
>> complete trace file is very big I trimmed it to show the time around this event
>> - hopefully this will contain the information you need. I would also like to
>> provide some additional information. The system on which I see these events had
>> a time that was _very_ wrong. I noticed that this issue occurs when
>> system-timesynd was one of the tasks calling the functions of interest to your
>> tracing and am wondering if a very out of sync time in process of being
>> corrected could be the cause of this issue? As an experiment I ensured the
>> system time was accurate before leaving the system idle overnight and I did not
>> see the issue the next morning.
> 
> Ah!  Yes, a sudden jump in time or a disagreement about the time among
> different components of the system can definitely cause these symptoms.
> We have sometimes seen these problems occur when a pair of CPUs have
> wildly different ideas about what time it is, for example.  Please let
> me know how it goes.
> 
> Also, in your trace, there are no sched_waking events for the rcu_preempt
> process that are not immediately followed by sched_wakeup, so your trace
> isn't showing the problem that I am seeing.

This is interesting.

Perhaps we could try with those commits reverted ?

commit e3baac47f0e82c4be632f4f97215bb93bf16b342
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date:   Wed Jun 4 10:31:18 2014 -0700

    sched/idle: Optimize try-to-wake-up IPI

commit fd99f91aa007ba255aac44fe6cf21c1db398243a
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date:   Wed Apr 9 15:35:08 2014 +0200

    sched/idle: Avoid spurious wakeup IPIs

They appeared in 3.16.

Thanks,

Mathieu

> 
> Still beating up on my stress test, which is not yet proving to be all
> that stressful.  :-/
> 
>							Thanx, Paul
> 
>> [  957.396537] INFO: rcu_preempt detected stalls on CPUs/tasks:
>> [  957.399933]  1-...: (0 ticks this GP) idle=4d6/0/0 softirq=6311/6311 fqs=0
>> [  957.403661]  (detected by 0, t=60002 jiffies, g=3583, c=3582, q=47)
>> [  957.407227] Task dump for CPU 1:
>> [  957.409964] swapper/1       R  running task        0     0      1 0x00200000
>> [  957.413770]  0000039daa9a7eb9 ffff8801785cfed0 ffffffff818af34c
>> ffff880100000000
>> [  957.417696]  0000000600000003 ffff8801785d0000 ffff880072f9ea00
>> ffffffff822dcf80
>> [  957.421631]  ffff8801785cc000 ffff8801785cc000 ffff8801785cfee0
>> ffffffff818af597
>> [  957.425562] Call Trace:
>> [  957.428124]  [<ffffffff818af34c>] ? cpuidle_enter_state+0xfc/0x310
>> [  957.431713]  [<ffffffff818af597>] ? cpuidle_enter+0x17/0x20
>> [  957.435122]  [<ffffffff811515ba>] ? call_cpuidle+0x2a/0x40
>> [  957.438467]  [<ffffffff8115198d>] ? cpu_startup_entry+0x28d/0x360
>> [  957.441949]  [<ffffffff8108c864>] ? start_secondary+0x114/0x140
>> [  957.445378] rcu_preempt kthread starved for 60002 jiffies! g3583 c3582 f0x0
>> RCU_GP_WAIT_FQS(3) ->state=0x1
>> [  957.449834] rcu_preempt     S ffff8801785b7d68     0     7      2 0x00000000
>> [  957.453579]  ffff8801785b7d68 ffff88017dc8cc80 ffff88016fe6bb80
>> ffff8801785abb80
>> [  957.457428]  ffff8801785b8000 ffff8801785b7da0 ffff88017dc8cc80
>> ffff88017dc8cc80
>> [  957.461249]  0000000000000003 ffff8801785b7d80 ffffffff81ab03df
>> 0000000100373021
>> [  957.465055] Call Trace:
>> [  957.467493]  [<ffffffff81ab03df>] schedule+0x3f/0xa0
>> [  957.470613]  [<ffffffff81ab4397>] schedule_timeout+0x127/0x270
>> [  957.473976]  [<ffffffff81171a00>] ? detach_if_pending+0x120/0x120
>> [  957.477387]  [<ffffffff8116d983>] rcu_gp_kthread+0x6d3/0xa40
>> [  957.480659]  [<ffffffff811513a0>] ? wake_atomic_t_function+0x70/0x70
>> [  957.484123]  [<ffffffff8116d2b0>] ? force_qs_rnp+0x1b0/0x1b0
>> [  957.487392]  [<ffffffff8112f856>] kthread+0xe6/0x100
>> [  957.490470]  [<ffffffff8112f770>] ? kthread_worker_fn+0x190/0x190
>> [  957.493859]  [<ffffffff81ab5ccf>] ret_from_fork+0x3f/0x70
>> [  957.497044]  [<ffffffff8112f770>] ? kthread_worker_fn+0x190/0x190
>> 
> > Reinette

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com