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

On 06/08/21 at 02:14pm, Andrew Morton wrote:

On Tue, 8 Jun 2021 22:24:32 +0800 Baoquan He [off-list ref] wrote:

quoted

On 06/08/21 at 06:33am, Pingfan Liu wrote:

quoted

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.

quoted

This looks good to me.

Acked-by: Baoquan He <redacted>

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.