linux-kernel - Re: [PATCH RFC] kexec: add option to print previous kernel release after kexec

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Message-ID: <ljo3xdbpwa2kzx5thlki6fc74mpswuwtfqzdl4qyatqi3qjbwm@4prhagytf2ja>
Date: Tue, 30 Dec 2025 07:11:10 -0800
From: Breno Leitao <leitao@...ian.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: Alexander Graf <graf@...zon.com>, Mike Rapoport <rppt@...nel.org>, 
	Pratyush Yadav <pratyush@...nel.org>, linux-kernel@...r.kernel.org, kexec@...ts.infradead.org, 
	linux-mm@...ck.org, usamaarif642@...il.com, rmikey@...a.com, clm@...com, 
	riel@...riel.com, kernel-team@...a.com
Subject: Re: [PATCH RFC] kexec: add option to print previous kernel release
 after kexec

Hello Pasha,


On Tue, Dec 30, 2025 at 10:03:38AM -0500, Pasha Tatashin wrote:
> On Tue, Dec 30, 2025 at 9:13 AM Breno Leitao <leitao@...ian.org> wrote:
> >
> > Introduce a new Kconfig option, CONFIG_KEXEC_SHOW_PREVIOUS_RELEASE,
> 
> I don't think we need a config for this. Let's just show the previous
> kernel version unconditionally when KHO is enabled.
> 
> > which enables the storage and display of the previous kernel's release
> > version across kexec boots when using Kexec Handover (KHO).
> >
> > Motivation
> > ==========
> >
> > Kernel bugs that depend on the version of the previously running kernel
> > are not uncommon, especially in scenarios where a buggy kernel kexecs
> > into a new one and the issue only manifests in the subsequent kernel.
> >
> > Recent examples include:
> >
> >  * eb2266312507 ("x86/boot: Fix page table access in 5-level to 4-level paging transition")
> >  * 77d48d39e991 ("efistub/tpm: Use ACPI reclaim memory for event log to avoid corruption")
> >  * 64b45dd46e15 ("x86/efi: skip memattr table on kexec boot")
> >
> > As kexec-based reboots become more widespread among Linux users, these
> > issues are becoming increasingly prominent.
> >
> > When such crashes occur, correlating them to the previous kernel version
> > is challenging, especially at scale, where the problem may only appear in
> > specific cases and it is hard to correlate.
> >
> > With the introduction of Kexec Handover (KHO), we now have a reliable
> > mechanism to pass information between kernels. This presents an
> > opportunity to address the problem by carrying the previous kernel's
> > release version to the next kernel and printing it at boot time.
> 
> LUO added the number of times a machine has been live updated to help
> debugging problems that are related to live update, perhaps, in
> addition to the previous kernel version, we should also add a number
> of times the machine has been kexec'd. It is useful when a bug
> manifests only after a number of kexec's which is also sometimes a
> case.

Thanks for bringing this up, I am on the same page as you here.

In fact, this was on my TODO list, but I didn't want to send in this RFC
to avoid too much changes/code.

I will wait a bit more and add the number of kexec'ed kernels in the
next revision.

Thanks for your input,
--breno