Re: [PATCH] crash_core, vmcoreinfo: Append 'SECTION_SIZE_BITS' to vmcoreinfo

Baoquan He
2021-06-09T02:47:29Z

On 06/08/21 at 02:14pm, Andrew Morton wrote:
> On Tue, 8 Jun 2021 22:24:32 +0800 Baoquan He <bhe@redhat.com> wrote:
>
> > On 06/08/21 at 06:33am, Pingfan Liu wrote:
> > > As mentioned in kernel commit 1d50e5d0c505 ("crash_core, vmcoreinfo:
> > > Append 'MAX_PHYSMEM_BITS' to vmcoreinfo"), SECTION_SIZE_BITS in the
> > > formula:
> > > #define SECTIONS_SHIFT (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
> > >
> > > Besides SECTIONS_SHIFT, SECTION_SIZE_BITS is also used to calculate
> > > PAGES_PER_SECTION in makedumpfile just like kernel.
> > >
> > > Unfortunately, this arch-dependent macro SECTION_SIZE_BITS changes, e.g.
> > > recently in kernel commit f0b13ee23241 ("arm64/sparsemem: reduce
> > > SECTION_SIZE_BITS"). But user space wants a stable interface to get this
> > > info. Such info is impossible to be deduced from a crashdump vmcore.
> > > Hence append SECTION_SIZE_BITS to vmcoreinfo.
> >
> > ...
> >
> > Add the discussion of the original thread in kexec ML for reference:
> > http://lists.infradead.org/pipermail/kexec/2021-June/022676.html
>
> I added a Link: for this.

Thanks, Andrew.

>
> > This looks good to me.
> >
> > Acked-by: Baoquan He <bhe@redhat.com>
>
> I'm thinking we should backport this at least to Fixes:f0b13ee23241.
> But perhaps it's simpler to just backport it as far as possible, so I
> added a bare cc:stable with no Fixes:. Thoughts?

Yeah, it should add cc:stable, thanks. Otherwise it will break
vmcore dumping on 5.12 stable kernel even though with the updated
makedumpfile utility. Fixes:f0b13ee23241 will help stable kernel
maintainer easier to identify which kernel this patch need be applied
on? If only having cc:stable with no Fixes is allowed, it's also OK.