Re: Purgatory compile flag changes apparently causing Kexec relocation overflows

[Steve Wahl]

On Wed, Aug 28, 2019 at 02:51:21PM -0700, Nick Desaulniers wrote:
> On Wed, Aug 28, 2019 at 12:42 PM Steve Wahl <steve.wahl@xxxxxxx> wrote:
> >
> > Please CC me on responses to this.
> >
> > I normally would do more diligence on this, but the timing is such
> > that I think it's better to get this out sooner.
> >
> > With the tip of the tree from https://github.com/torvalds/linux.git  (a
> > few days old, most recent commit fetched is
> > bb7ba8069de933d69cb45dd0a5806b61033796a3), I'm seeing "kexec: Overflow
> > in relocation type 11 value 0x11fffd000" when I try to load a crash
> > kernel with kdump. This seems to be caused by commit
> > 059f801a937d164e03b33c1848bb3dca67c0b04, which changed the compiler
> > flags used to compile purgatory.ro, apparently creating 32 bit
> > relocations for things that aren't necessarily reachable with a 32 bit
> > reference.  My guess is this only occurs when the crash kernel is
> > located outside 32-bit addressable physical space.
> >
> > I have so far verified that the problem occurs with that commit, and
> > does not occur with the previous commit.  For this commit, Thomas
> > Gleixner mentioned a few of the changed flags should have been looked
> > at twice.  I have not gone so far as to figure out which flags cause
> > the problem.
> >
> > The hardware in use is a HPE Superdome Flex with 48 * 32GiB dimms
> > (total 1536 GiB).
> >
> > One example of the exact error messages seen:
> >
> > 019-08-28T13:42:39.308110-05:00 uv4test14 kernel: [   45.137743] kexec: Overflow in relocation type 11 value 0x17f7affd000
> > 2019-08-28T13:42:39.308123-05:00 uv4test14 kernel: [   45.137749] kexec-bzImage64: Loading purgatory failed
> 
> Thanks for the report and sorry for the breakage.  Can you please send
> me more information for how to precisely reproduce the issue?  I'm
> happy to look into fixing it.

Here's the details I know might be important:

Since this appears to be a problem with the result of a relocation not
fitting within 32 bits, I think the location chosen to place the crash
kernel needs to be above 4GiB; so you need a machine with more memory
than that.

At the moment I'm running SLES 12 sp 4 as the rest of the
environment.  rpm says kdump is kdump-0.8.16-9.2.x86_64.  I've fetched
the kernel sources and compiled directly on this system.  I believe I
copied the kernel config from the SLES kernel and did a make
olddefconfig for configuration.  Made and installed the kernel from
the kernel tree.

crashkernel=512M,high is set on the command line.

As the system boots, and systemd initializes kdump, it tries to load
the crash kernel, I believe through
/usr/lib/systemd/system/kdump.service running /lib/kdump/load.sh
--update.

Once that completes, 'systemctl status kdump' indicates a failure, and
dmesg | grep kexec shows the error messages mentioned above.

> Let me go dig up the different listed flags.  Steve, it may be fastest
> for you to test re-adding them in your setup to see which one is
> important.

I will work through that tomorrow and let you know what I find.

> Tglx, if you want to revert the above patches, I'm ok with that.  It's
> important that we fix the issue eventually that my patches were meant
> to address, but precisely *when* it's solved isn't critical; our
> kernels can carry out of tree patches for now until the issue is
> completely resolved worst case.
> -- 
> Thanks,
> ~Nick Desaulniers

Thank you!

--> Steve Wahl

-- 
Steve Wahl, Hewlett Packard Enterprise