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Can't capture vmcore?

I'm getting kernel panics in a VM that functions as a hypervisor, the
moment I spin up the nested guest (on AMD ThreadRipper / Fedora 27). That
is annoying, of course, so I try to be a good citizen and file a bug.

For some reason though, I cannot get the core dumped. I get a core fine
with sysrq, but not with this actual panic. I've followed [1] to set up
kdump and crash, but everytime I trigger the crash and see my VM reboot, I
see an empty /var/crash afterwards.

As was able to get the vmcore written to /var/crash on in a RHEL7 guest,
I'm starting to suspect a bug, but I'm unsure.

Any pointers on how to debug this?

[1] <a href="https://fedoraproject.org/wiki/How_to_use_kdump_to_debug_kernel_crashes" title="https://fedoraproject.org/wiki/How_to_use_kdump_to_debug_kernel_crashes">https://fedoraproject.org/wiki/How_to_use_kdump_to_debug_kernel_crashes</a>

Comments

Re: Can't capture vmcore?

By Josh Boyer at 01/16/2018 - 08:41

On Tue, Jan 9, 2018 at 1:51 PM, Maxim Burgerhout < ... at wzzrd dot com> wrote:
Adding the Fedora kernel list.

Kdump isn't automatically tested in Fedora and while it can work, it
can often be broken as well. There might be someone on the kernel
list that is more familiar with the current state of kdump support in
Fedora, or alternative methods for getting the kernel backtrace.

josh

Re: Can't capture vmcore?

By Juan Orti Alcaine at 01/16/2018 - 10:58

2018-01-16 13:41 GMT+01:00 Josh Boyer < ... at fedoraproject dot org>:

​​I'm also interested in this, because I have a reproducible system crash
but I can't ​capture the vmcore, the crash kernel only writes the dmesg.​