Re: BUG: rcu_sched detected stalls on CPUs

Paul E. McKenney
2017-05-08T13:24:29Z

On Mon, May 08, 2017 at 09:43:15AM +0300, mitko@stz-bg.com wrote:
> On 2017-01-20 17:19, Steven Rostedt wrote:
> >On Fri, 20 Jan 2017 10:43:50 +0200
> >mitko@stz-bg.com wrote:
> >
> >>[1.] One line summary of the problem:
> >>
> >>rcu_sched detected stalls on CPUs and few minutes server not respond.
> >
> >Is this reproducible? Or was this a one time ordeal?
> >
> >>
> >>[2.] Full description of the problem/report:
> >>
> >>Load of my server (postgres database) isnt big less then 0.50 and when
> >>error occured rcu_sched detected stalls on CPUs
> >>server freeze and nothing is work for 3-5 minute.
> >>No network, no video signal, no keyboard, no mouse. Nothing is worked.
> >>After these few minutes everything continue normal.
> >>This usual is happend once per day. When I check in google find a lots
> >>of ppl complain of this error, but no solution.
> >>Do any one know can help me to resolve it ? I spoke with few
> >>friends and
> >>they trying to convince me the problem is in CPU.
> >>I did not believe after a 3 years working CPU suddenly stop working
> >>correctly, but I might be wrong.
> >>
> >>[3.] Keywords (i.e., modules, networking, kernel):
> >>
> >>kernel
> >>
> >>[4.] Kernel information
> >>[4.1.] Kernel version (from /proc/version):
> >>
> >>Linux version 4.4.38 (root@hive64) (gcc version 5.4.0 (GCC) ) #2
> >>SMP Sun
> >>Dec 11 16:11:02 CST 2016
> >>
> >
> >Have you tried a newer version of the kernel?
> >
> >-- Steve
>
>
> Hello,
> yesterday I change to new kernel: 4.9.26 and still no effect.
>
> I trying to figure out what I need to buy because I read on google a
> lots of posts about that problem,
> some ppl suggest is BIOS firmware bug, some ppl tell that when they
> swap CPU problem is resolved.
> May be problem was started when I first time boot 4.x kernel and
> there have cpu microcode updates.
> Im 3.x kernels this feature was not in kernel, but I don't know,
> only guess.
>
> Can some one point me clearly: You need to change this one and
> problem will be solved ?

Looking back at your earlier email, I see the following:

[Wed Jan 4 10:19:12 2017] rcu_sched kthread starved for 60004 jiffies! g61967937 c61967936 f0x0 s3 ->state=0x1

That indicates that the task "rcu_sched" isn't being allowed to run.
The "->state=0x1" indicates that this task is currently asleep and the
"s3" indicates that it is looking to start a grace period, but has not
progressed through this task. My guess is that your system get very
busy, and that rcu_sched's normal scheduling priority is not sufficient
for it to be allowed to run.

I therefore suggest that you try raising the rcu_sched task's priority.

You can find this task like this:

ps -ef | grep rcu_sched

On my laptop, I get this:

$ ps -ef | grep rcu_sched
root 7 2 0 Apr11 ? 00:19:19 [rcu_sched]
paulmck 18307 22926 0 06:11 pts/35 00:00:00 grep --color=auto rcu_sche

You can use the chrt command to set the priority. For example, given that
on my laptop, rcu_sched is PID 7:

sudo chrt -f -p 1 7

You can double-check as follows:

$ chrt -p 7
pid 7's current scheduling policy: SCHED_FIFO
pid 7's current scheduling priority: 1

Does that help?

Thanx, Paul

> [239940.067938] clocksource: timekeeping watchdog on CPU26: Marking
> clocksource 'tsc' as unstable because the skew is too large:
> [239940.067943] clocksource: 'hpet' wd_now:
> ecb521ce wd_last: ca45912d mask: ffffffff
> [239940.067946] clocksource: 'tsc' cs_now:
> 2d12df5f88d08 cs_last: 29fffbe2d36d6 mask: ffffffffffffffff
> [239940.068357] clocksource: Switched to clocksource hpet
> [240000.066457] INFO: rcu_sched detected stalls on CPUs/tasks:
> [240000.066488] 2-...: (38 GPs behind) idle=f1a/0/0
> softirq=2417028/2417028 fqs=0
> [240000.066491] 3-...: (27 GPs behind) idle=0bc/0/0
> softirq=3076046/3076047 fqs=0
> [240000.066494] 4-...: (1006 GPs behind) idle=308/0/0
> softirq=1474922/1474922 fqs=0
> [240000.066497] 5-...: (8034 GPs behind) idle=7b4/0/0
> softirq=69165/69166 fqs=0
> [240000.066499] 6-...: (1665 GPs behind) idle=716/0/0
> softirq=16465/16465 fqs=0
> [240000.066502] 7-...: (8034 GPs behind) idle=bd0/0/0
> softirq=15923/15924 fqs=0
> [240000.066505] 8-...: (1665 GPs behind) idle=a62/0/0
> softirq=93861/93861 fqs=0
> [240000.066507] 9-...: (1258 GPs behind) idle=a8c/0/0
> softirq=21608/21608 fqs=0
> [240000.066510] 11-...: (1665 GPs behind) idle=8e6/0/0
> softirq=18844/18844 fqs=0
> [240000.066512] 13-...: (1665 GPs behind) idle=ab8/0/0
> softirq=21278/21278 fqs=0
> [240000.066515] 14-...: (4854 GPs behind) idle=578/0/0
> softirq=25624/25626 fqs=0
> [240000.066517] 15-...: (8034 GPs behind) idle=f5e/0/0
> softirq=18114/18115 fqs=0
> [240000.066520] 16-...: (1665 GPs behind) idle=b66/0/0
> softirq=19511/19511 fqs=0
> [240000.066528] 17-...: (0 ticks this GP) idle=e18/0/0
> softirq=16163/16163 fqs=0
> [240000.066531] 18-...: (1665 GPs behind) idle=a18/0/0
> softirq=16424/16424 fqs=0
> [240000.066533] 19-...: (1665 GPs behind) idle=944/0/0
> softirq=17920/17920 fqs=0
> [240000.066549] 20-...: (20991 GPs behind) idle=750/0/0
> softirq=17549/17552 fqs=0
> [240000.066552] 21-...: (0 ticks this GP) idle=9e0/0/0
> softirq=18937/18937 fqs=0
> [240000.066555] 22-...: (14519 GPs behind) idle=95e/0/0
> softirq=16122/16124 fqs=0
> [240000.066557] 23-...: (1665 GPs behind) idle=bbc/0/0
> softirq=16316/16316 fqs=0
> [240000.066560] 24-...: (0 ticks this GP) idle=c56/0/0
> softirq=20070/20070 fqs=0
> [240000.066563] 27-...: (8034 GPs behind) idle=bdc/0/0
> softirq=18291/18292 fqs=0
> [240000.066566] 28-...: (8034 GPs behind) idle=4f8/0/0
> softirq=22313/22314 fqs=0
> [240000.066568] 29-...: (3443 GPs behind) idle=22a/0/0
> softirq=24975/24976 fqs=0
> [240000.066571] 30-...: (1665 GPs behind) idle=940/0/0
> softirq=89382/89382 fqs=0
> [240000.066572] (detected by 10, t=60002 jiffies, g=4843721,
> c=4843720, q=659)
> [240000.066578] Task dump for CPU 2:
> [240000.066581] swapper/2 R running task 0 0
> 1 0x00200000
> [240000.066588] 0000000000000083 ffffffffa5cecd79 ffff8aca3eea1e00
> ffffffffa64cab40
> [240000.066593] 0000000000000005 ffffffffa64cad38 ffffa96c80073eb0
> ffffffffa5ba9d93
> [240000.066597] ffff8aca3eea1e00 000000000e94fec6 ffff8aca38535940
> 0000000000000002
> [240000.066601] Call Trace:
> [240000.066617] [<ffffffffa5cecd79>] ? intel_idle+0x109/0x110
> [240000.066625] [<ffffffffa5ba9d93>] ? cpuidle_enter_state+0x103/0x2b0
> [240000.066629] [<ffffffffa5ba9f77>] ? cpuidle_enter+0x17/0x20
> [240000.066638] [<ffffffffa50d5d73>] ? call_cpuidle+0x23/0x40
> [240000.066641] [<ffffffffa50d5fd7>] ? cpu_startup_entry+0x147/0x220
> [240000.066647] [<ffffffffa503ecfd>] ? start_secondary+0x12d/0x140
> [240000.066650] Task dump for CPU 3:
> [240000.066651] swapper/3 R running task 0 0
> 1 0x00200000
>
> Regards,
> Mitko
>