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== Comment: #0 - Ping Tian Han <pthan@xxxxxxxxxx> - 2015-07-15 04:21:23 ==
---Problem Description---
kdump can be triggered by "echo c > /proc/sysrq-trigger', but the second kernel hangs here:

...
[    7.311129] sd 0:2:4:0: alua: rtpg failed with 8070002
[    7.311232] sd 0:2:4:0: alua: port group 1dc state A preferred supports TOlUSNA
done.
Begin: Running /scripts/local-premount ... done.
[   12.894379] EXT4-fs (dm-12): mounted filesystem with ordered data mode. Opts: (null)
Begin: Running /scripts/local-bottom ... done.
done.
Begin: Running /scripts/init-bottom ... done.
[   13.463955] init: plymouth-upstart-bridge main process (1681) terminated with status 1
[   13.463996] init: plymouth-upstart-bridge main process ended, respawning
[   13.471552] init: plymouth-upstart-bridge main process (1691) terminated with status 1
[   13.471586] init: plymouth-upstart-bridge main process ended, respawning
[   13.479547] init: plymouth-upstart-bridge main process (1694) terminated with status 1
[   13.479580] init: plymouth-upstart-bridge main process ended, respawning
[   13.487503] init: plymouth-upstart-bridge main process (1696) terminated with status 1
[   13.487536] init: plymouth-upstart-bridge main process ended, respawning
[   13.496113] init: plymouth-upstart-bridge main process (1698) terminated with status 1
[   13.496146] init: plymouth-upstart-bridge main process ended, respawning
[   13.504363] init: plymouth-upstart-bridge main process (1700) terminated with status 1
[   13.504397] init: plymouth-upstart-bridge main process ended, respawning
[   13.512840] init: plymouth-upstart-bridge main process (1702) terminated with status 1
[   13.512873] init: plymouth-upstart-bridge main process ended, respawning
[   13.521159] init: plymouth-upstart-bridge main process (1704) terminated with status 1
[   13.521196] init: plymouth-upstart-bridge main process ended, respawning
[   13.531934] init: plymouth-upstart-bridge main process (1706) terminated with status 1
[   13.531968] init: plymouth-upstart-bridge main process ended, respawning
[   13.548264] init: plymouth-upstart-bridge main process (1708) terminated with status 1
[   13.548301] init: plymouth-upstart-bridge main process ended, respawning
[   14.774719] EXT4-fs (dm-12): re-mounted. Opts: errors=remount-ro
<-----------
and no vmcore dumpped.
 
Contact Information = Ping Tian Han/pthan@xxxxxxxxxx, 	Mikhail Afanasiev/afanasie@xxxxxxxxxx 
 
---uname output---
Linux dilllp1 3.19.0-22-generic #22~14.04.1-Ubuntu SMP Wed Jun 17 10:03:39 UTC 2015 ppc64le ppc64le ppc64le GNU/Linux
 
 
---System Hang---
 the booting process of the second kernel hangs. We have to reboot the  system.
 
---Debugger---
A debugger is not configured
 
---Steps to Reproduce---
 1. install ubuntu on dilllp1, which root device is on a mpath device
2. sudo apt-get install linux-crashdump
3. change the crashkerenl= parameter in /boot/grub/grub.cfg to 'crashkernel=768M', then reboot
4. trigger kdump by 'echo c > /proc/sysrq-trigger'
 
Userspace tool common name: kdump-tools 
 
The userspace tool has the following bit modes: 64-bit 

== Comment: #8 - Ping Tian Han <pthan@xxxxxxxxxx> - 2015-12-09 02:09:30 ==
We can reproduce this bug with kernel 4.2.0-19.

== Comment: #12 - Hari Krishna Bathini <hbathini@xxxxxxxxxx> - 2015-12-09 08:22:27 ==
Is the issue only seen with sysctl configuration
"vm.min_free_kbytes = 312721" ?

Thanks
Hari

== Comment: #13 - Ping Tian Han <pthan@xxxxxxxxxx> - 2015-12-09 21:08:54 ==
(In reply to comment #12)
> Is the issue only seen with sysctl configuration
> "vm.min_free_kbytes = 312721" ?
> 

Yes, I just found that if use the default min_free_kbytes value then
kdump works just fine!

== Comment: #14 - Hari Krishna Bathini <hbathini@xxxxxxxxxx> - 2015-12-10 00:51:43 ==
(In reply to comment #13)
> (In reply to comment #12)
> > Is the issue only seen with sysctl configuration
> > "vm.min_free_kbytes = 312721" ?
> > 
> 
> Yes, I just found that if use the default min_free_kbytes value then kdump
> works just fine!

It is blocking kdump from utilising the memory needed to boot.
So, crashkernel=768M with min_free_kbytes configured to
312721 translates to ~450 MB for second kernel boot (kdump)
which doesn't seem to be sufficient for booting.

How to handle this:

1. Reserve memory for crashkernel, that augments it by min_free_kbytes

    OR

2. Use default min_free_kbytes

Thanks
Hari

== Comment: #16 - Ping Tian Han <pthan@xxxxxxxxxx> - 2015-12-10 01:27:40 ==
(In reply to comment #14)
> (In reply to comment #13)
> > (In reply to comment #12)
> > > Is the issue only seen with sysctl configuration
> > > "vm.min_free_kbytes = 312721" ?
> > > 
> > 
> > Yes, I just found that if use the default min_free_kbytes value then kdump
> > works just fine!
> 
> It is blocking kdump from utilising the memory needed to boot.
> So, crashkernel=768M with min_free_kbytes configured to
> 312721 translates to ~450 MB for second kernel boot (kdump)
> which doesn't seem to be sufficient for booting.
> 
> How to handle this:
> 
> 1. Reserve memory for crashkernel, that augments it by min_free_kbytes
> 
>     OR
> 
> 2. Use default min_free_kbytes
> 
> Thanks
> Hari

Is it possible that let kdump ignoreis the min_free_kbytes when being
triggered? We need a large min_free_kbytes to run stress tests, but
kdump doesn't need it.

== Comment: #19 - Hari Krishna Bathini <hbathini@xxxxxxxxxx> - 2015-12-20 13:44:12 ==
Ubuntu uses default initrd and kernel image to boot into kdump
as well. So, the same sysctl settings (runtime parameters)
apply for kdump as well. It is difficult to have one sysctl
setting for production kernel and another for kdump kernel
for this reason.

---
You can workaround this by using a non-persistent sysctl
setting in production kernel for vm.min_free_kbytes.

I mean, remove "vm.min_free_kbytes = 312721" from sysctl
configuration files and set it with the below command:

        # sudo sysctl vm.min_free_kbytes=312721

This way, kdump gets to use the default vm.min_free_kbytes
setting and production kernel could use the value you set.
---

If you wish to have a different soultion, please mirror the
bug and see what Ubuntu has to say about this..

Thanks
Hari

** Affects: linux (Ubuntu)
     Importance: Undecided
     Assignee: Canonical Kernel Team (canonical-kernel-team)
         Status: New


** Tags: architecture-ppc64le bot-comment bugnameltc-127681 severity-high targetmilestone-inin14043
-- 
ISST-LTE: kdump failed: second kernel booting hangs after /scripts/init-bottom when large min_free_kbytes value being set
https://bugs.launchpad.net/bugs/1528101
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