Message-ID: <e33d354978447db931aec584e0de6d52@stz-bg.com>
Date:   Wed, 10 May 2017 14:00:32 +0300
From:   mitko@...-bg.com
To:     paulmck@...ux.vnet.ibm.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 2017-05-09 17:49, Paul E. McKenney wrote:
> On Tue, May 09, 2017 at 10:53:25AM +0300, mitko@...-bg.com wrote:
>> On 2017-05-08 16:24, Paul E. McKenney wrote:
>> >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Have you tried a newer version of the kernel?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
>> >
>> 
>> 
>> Hi,
>> interesting ... I change priority as you suggest and will keep you
>> in touch
>> if the problem happens again because I cant reproduce it. Replay on
>> your next email, I don't have any
>> virtual servers / guest os on the server. It's server with only one
>> process - redis server
>> and in this time when error it's happened actually one of other
>> servers start loading data
>> into redis sever. Data is small 3-4 mil. keys every key contain
>> around 150 symbols.
>> I have that problem on two servers, next server is database server
>> with postgresql
>> and that problem happened more often, usual once per day or for few
>> days.
>> I never play before with changing priority of processes. When I check
>> iLO log I saw logged error: power lost but server does not lost the
>> power actually,
>> it's just stop respond for 2-3 minutes and then continue normal
>> operation with
>> uptime more then 100 days.
> 
> Does redis keep any useful log?  If so, it would be worth looking into
> what it thought that it was doing.


No,

only standard logs:

1333:M 06 May 04:36:43.019 * 10000 changes in 60 seconds. Saving...
1333:M 06 May 04:36:43.025 * Background saving started by pid 4325
4325:C 06 May 04:36:46.745 * DB saved on disk
4325:C 06 May 04:36:46.749 * RDB: 40 MB of memory used by copy-on-write
1333:M 06 May 04:36:46.825 * Background saving terminated with success
1333:M 06 May 04:37:47.018 * 10000 changes in 60 seconds. Saving...
1333:M 06 May 04:37:47.026 * Background saving started by pid 4326
4326:C 06 May 04:37:50.902 * DB saved on disk
4326:C 06 May 04:37:50.907 * RDB: 208 MB of memory used by copy-on-write
1333:M 06 May 04:37:50.926 * Background saving terminated with success


Don't know if that information is valued, but before loading data server 
does not
do anything for last 3-4 hours and probably kernel put some processes in 
sleeping mode
  then data is begin loaded. Logs tell us
10k changes for few seconds until all data of 3-4 mil keys is loaded.
May be, as you suggest kernel can not start the processes so quickly.
Last night I does not have that problem, but for the moment I can not 
confirm
the suggested solution is worked.

Regards,
Mitko




> 
> 							Thanx, Paul
> 
>> Thanks for your suggestion.
>> Regards,
>> Mitko
>> 
>> 
>> 
>> 
>> >>[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
>> >>
>> 

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