kexec does not work for kernel version with patch level >= 256

[Patrick Sung]

On Wed, Mar 31, 2021 at 10:47 AM Baoquan He <bhe at redhat.com> wrote:
>
> On 03/24/21 at 12:28pm, Patrick Sung wrote:
> > Hello all,
> >
> > I am using the 4.9 long term kernel which is currently at 4.9.262.
> > When using this kernel with kexec-tools it prints out this error
> >
> >   Unsupported utsname.release: 4.9.262
> >   Cannot load <kdump images path>
> >
> > A quick search in the code shows that kexec/kernel_version.c doing this check:
> >
> >   if (major >= 256 || minor >= 256 || patch >= 256) {
> >
> > and also in kexec/kexec.h
> >   #define KERNEL_VERSION(major, minor, patch) \
> >     (((major) << 16) | ((minor) << 8) | patch)
>
> Yeah, this seems to be a good catch. The existing longterm kenrel 4.9.262
> does cause the problem. I am not very sure about the longterm kernel
> version numbering, maybe we can leave 16 bits for for patch number to
> avoid the longterm kernel issue?
>
> Is there document telling the longterm kernel version numbering, or any
> pointer?
>
Actually I found that the mainline kernel clamp the "patch" version to 255

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/Makefile?id=9b82f13e7ef316cdc0a8858f1349f4defce3f9e0

> Thanks
> Baoquan
>
> >
> > which explains the reason for the range check in kernel_version.c
> >
> > Increasing the number of bits allowed in "patch" seems to fix the issue.
> >
> > Thanks,
> > Patrick
> >
> > _______________________________________________
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> > http://lists.infradead.org/mailman/listinfo/kexec
> >
>