Public bug reported:

When linux-crashdump (5.4.0.58.61) is enabled on Ubuntu 20.04 LTS,
everything appears to be in good working order, according to "systemctl
status kdump-tools" and "kdump-config status". However, upon an actual
crash, the system hangs, and no crash files are produced. I've
investigated and have learned that the capture kernel does indeed start,
but it is unable to unpack the rootfs/initrd, and thus fails and hangs.

[    1.070469] Trying to unpack rootfs image as initramfs...
[    1.333182] swapper/0 invoked oom-killer: gfp_mask=0x100cc2(GFP_HIGHUSER), 
order=0, oom_score_adj=0
[    1.335074] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.4.0-26-generic 
#30-Ubuntu 
[    1.336396] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
Ubuntu-1.8.2-1ubuntu1 04/01/2014
[    1.336396] Call Trace:
[    1.336396]  dump_stack+0x6d/0x9a
[    1.336396]  dump_header+0x4f/0x1eb
[    1.336396]  out_of_memory.part.0.cold+0x39/0x83
[    1.336396]  out_of_memory+0x6d/0xd0
...
[    1.413202] ---[ end Kernel panic - not syncing: System is deadlocked on 
memory ]---


On this system with 8G of memory, the crash memory as specified on the kernel 
command line is "crashkernel=512M-:192M". I changed the 192M to 256M, and now 
kdump works.

Not sure how the 192M value is chosen, but it does not work. I think
this used value used to work for 16.04 and maybe 18.04 (I didn't try),
but is no longer useful for 20.04.

** Affects: kexec-tools (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1908090

Title:
  ubuntu 20.04 kdump fails

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