[Bug 1728115] [NEW] crashkernel offset prevents kernel boot

[Launchpad Bug Tracker]

You have been subscribed to a public bug by Ubuntu Foundations Team Bug Bot (crichton):

[Impact]
On Power Systems, the kernel won't boot when given a crashkernel parameter with an offset/start address of 32M. No output will be shown, giving no clue to the user why the system has not booted, or what the problem is.

[Test Case]
Installing kdump-tools on artful, then booting the system. It won't boot. With the fix, it boots and the crash kernel is reserved.

[Regression Potential]
Some Power Systems might have problems loading the kernel at this address. LP#1567539 is not really clear if PowerNV systems won't kdump when using an address different from 32M. However, it has been requested from an IBM person to test it with 128M instead, and no particular problem was shown. It's possible that there was no reason at first to use 32M, and no problems will be found on either PowerNV or other systems on the field. On the other hand, it's possible they might break kdump. But, right now, those systems won't even boot the first kernel without this change.

----

The linux kernel won't boot when crashkernel parameter tells it to load
a crash kernel at 32Mi on ppc64el on artful.

This happens because the artful kernel is too big. In fact, multiple
requirements on the architecture lead to that:

Kernel memory at address 0 is reserved.
crashkernel must be at first RMO, so architecture puts it at 128Mi. However, kdump-tools currently puts it at @32Mi because of bug https://bugs.launchpad.net/ubuntu/+source/makedumpfile/+bug/1567539.
PACA and LPPACA need to be at the first RMO as well, and with 2048 CPUs, they take more than 5MB and 2MiB, respectively.

With the kernel now taking around 25MB from stext to _end, the kernel
can't reserve enough memory for PACA or LPPACA right after boot, and it
panics.

So, right after installing kdump-tools on artful, and rebooting, the
kernel won't boot, with no sign of life as we haven't even started any
console. Investigation for this issue took an entire day.

The fix would be setting the loading address to 128MiB, and start
reducing size of PACA and maybe remove some of the requirements for the
location of PACA and crash kernel.

I would not even set the loading address of the crash kernel in the
parameter itself, and leave it to the kernel to decide it, which it
already does and already would put it at 128Mi.

Cascardo.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Incomplete

** Affects: makedumpfile (Ubuntu)
     Importance: Undecided
     Assignee: Thadeu Lima de Souza Cascardo (cascardo)
         Status: In Progress


** Tags: patch
-- 
crashkernel offset prevents kernel boot
https://bugs.launchpad.net/bugs/1728115
You received this bug notification because you are a member of Ubuntu Sponsors Team, which is subscribed to the bug report.