Bug 1773478

Summary: [Hyper-V][RHEL7.9 kexec-tools doc]kdump does not support nr_cpus=X (X>1) in vm on Hyper-V host
Product: Red Hat Enterprise Linux 7 Reporter: HuijingHei <hhei>
Component: kexec-toolsAssignee: Kairui Song <kasong>
Status: CLOSED ERRATA QA Contact: HuijingHei <hhei>
Severity: low Docs Contact: Jiri Herrmann <jherrman>
Priority: low    
Version: 7.8CC: bhsharma, cye, hhei, huzhao, kasong, ribarry, ruyang, vkuznets, xiaofwan, xuli, yacao, yuxisun
Target Milestone: rc   
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: kexec-tools-2.0.15-47.el7 Doc Type: Known Issue
Doc Text:
.kdump does not support setting nr_cpus to 2 or higher in Hyper-V virtual machines When using RHEL 7.9 as a guest operating system on a Microsoft Hyper-V hypervisor, the kdump kernel in some cases becomes unresponsive when the `nr_cpus` parameter is set to 2 or higher. To avoid this problem from occurring, do not change the default `nr_cpus=1` parameter in the `/etc/sysconfig/kdump` file of the guest.
 Story Points: ---
Clone Of: Environment:
Last Closed: 2020-09-29 19:37:08 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 1771898    
Attachments:
Description Flags
kdump serial logs with nr_cpus=2 none

Description HuijingHei 2019-11-18 09:04:56 UTC 
Description of problem:
Kdump works with default nr_cpus=1 in /etc/sysconfig/kdump, if set nr_cpus=2, kdump kernel crash, the issue is discussed in https://bugzilla.redhat.com/show_bug.cgi?id=1724993#c28

Version-Release number of selected component (if applicable):
vm: 16G memory, 4 vcpus, kernel-3.10.0-1112.el7.x86_64
Host: 2016, gen2

How reproducible:
100%

Steps to Reproduce:
1. Start guest and update /etc/sysconfig/kdump(KDUMP_COMMANDLINE_APPEND) with nr_cpus=2 
# kdumpctl restart
# kdumpctl status
Kdump is operational

2. trigger kdump
# echo c > /proc/sysrq-trigger

Actual results:
kdump kernel crash

Expected results:


Additional info:
1. For the console log, can see the attachment
2. Test with rhel8.1, no such issue
Comment 2 HuijingHei 2019-11-18 09:05:55 UTC 
Created attachment 1637239 [details]
kdump serial logs with nr_cpus=2

Attach the serial logs
Comment 11 HuijingHei 2020-03-27 03:21:53 UTC 
Check kexec-kdump-howto.txt in kexec-tools-2.0.15-47.el7.src.rpm, there is note about the bug:
On HyperV systems, only nr_cpus=1 is supported, if nr_cpus value is larger than 1, capture kernel may hang at boot.

Change bug status to verified
Comment 14 Kairui Song 2020-03-30 07:20:51 UTC 
The doc text looks good to me, thanks.
Comment 20 errata-xmlrpc 2020-09-29 19:37:08 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (kexec-tools bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2020:3885