linux-kernel - RE: Weird SysRq's during reboot

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Message-ID: <139f01d41468$dbc51e70$934f5b50$@bytehouse.co.uk>
Date:   Thu, 5 Jul 2018 15:02:45 +0100
From:   "Alan" <alan@...ehouse.co.uk>
To:     <linux-kernel@...r.kernel.org>
Subject: RE: Weird SysRq's during reboot

Panic over. It seems that my OnApp control server, when it loses contact
with a compute node, sends an snmptrap command to force a reboot of that
node. The trap script on the server uses sysrq-trigger, first "s", then "u",
then "b".

Please accept my apologies if you wasted any time on this.

Regards,  Alan Griffiths

Bytehouse

-----Original Message-----
From: Alan [mailto:alan@...ehouse.co.uk] 
Sent: 05 July 2018 11:19
To: 'linux-kernel@...r.kernel.org' <linux-kernel@...r.kernel.org>
Subject: Weird SysRq's during reboot

Hello everyone, this is my first time posting to this list so please be
gentle.

I have a server, hardware spec:

         HP DL360p G8
           2 x Intel Xeon E5-2620 Hex-Core 2GHz processors
           150GB Ram
           Embedded HP Ethernet 1Gb 4-port 331FLR Adapter
           Embedded Smart Array P420i Controller
           PCI-E Slot 1 HP Ethernet 10Gb 2-port 530SFP+ Adapter

which I am trying to configure as an OnApp compute engine. Recently I have
seen the following weird behaviour:

         1. Login on the server as root
         2. Enter a 'shutdown -r now' command
         3. Watch the reboot on the iLO console
         4. System reboots except that right at the end, after the login
prompt appears on the console, I see:

                  SysRq: Emergency Sync
                  Emergency Sync complete
                  SysRq : Emergency Remount R/O

              And then the system reboots again.
         5. The second reboot always works without the SysRq.

Looking in /var/log/messages I see, just prior to the second reboot (*):

         Jul  5 10:30:17 hv08 kernel: Ebtables v2.0 registered
         Jul  5 10:30:17 hv08 kernel: Bridge firewalling registered
         Jul  5 10:30:17 hv08 kernel: arp_tables: (C) 2002 David S. Miller
         Jul  5 10:30:18 hv08 kernel: lo: Disabled Privacy Extensions
*        Jul  5 10:30:27 hv08 kernel: SysRq : Emergency Sync
*        Jul  5 10:30:27 hv08 kernel: Emergency Sync complete
*        Jul  5 10:30:28 hv08 kernel: SysRq : Emergency Remount R/O
         Jul  5 10:33:43 hv08 kernel: imklog 5.8.10, log source = /proc/kmsg
started.
         Jul  5 10:33:43 hv08 rsyslogd: [origin software="rsyslogd"
swVersion="5.8.10" x-pid="2491" x-info="http://www.rsyslog.com"] start
         Jul  5 10:33:43 hv08 kernel: Initializing cgroup subsys cpuset
         Jul  5 10:33:43 hv08 kernel: Initializing cgroup subsys cpu
         Jul  5 10:33:43 hv08 kernel: Linux version
2.6.32-696.30.1.el6.x86_64 (mockbuild@...l.rdu2.centos.org) (gcc version
4.4.7 20120313 (Red Hat 4.4.7-18) (GCC) ) #1 SMP Tue May 22 03:28:18 UTC
2018
         Jul  5 10:33:43 hv08 kernel: Command line: ro
root=UUID=eafc533f-c5cb-4c89-bc0d-33125ab7f9d9 nomodeset rd_NO_LUKS
KEYBOARDTYPE=pc KEYTABLE=uk LANG=en_US.UTF-8 rd_NO_MD
SYSFONT=latarcyrheb-sun16 crash kernel=auto rd_NO_LVM rd_NO_DM rhgb quiet

I have tried booting the 2.6.32-696.28.1.el6.x86_64  and the
2.6.32-696.el6.x86_64  kernels with the same result. The problem does not
occur if I boot from the Centos 6.9 liveDVD iso which also uses kernel
version 2.6.32-696.el6.x86_64.

So, I am hoping someone here can answer any of these questions for me:

         A. What have I done to make this happen?
         B. Is there a way I can fix it?
         C. If not is there some other way to stop it happening?

Thank you for taking the time to read this email. I shall look forward to
hearing from you. Please CC me on any replies.

Regards, Alan Griffiths

Bytehouse