linux-kernel - Re: BUG: rcu_sched detected stalls on CPUs

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Date:   Mon, 8 May 2017 06:24:23 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     mitko@...-bg.com
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        linux-kernel@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: BUG: rcu_sched detected stalls on CPUs

On Mon, May 08, 2017 at 09:43:15AM +0300, mitko@...-bg.com wrote:
> On 2017-01-20 17:19, Steven Rostedt wrote:
> >On Fri, 20 Jan 2017 10:43:50 +0200
> >mitko@...-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@...e64) (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Have you tried a newer version of the kernel?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
>