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Mon, 05 Jan 2026 02:47:41 -0800 (PST) Date: Mon, 5 Jan 2026 02:47:39 -0800 From: Breno Leitao To: Pratyush Yadav Cc: Alexander Graf , Mike Rapoport , Pasha Tatashin , linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org, usamaarif642@gmail.com, rmikey@meta.com, clm@fb.com, riel@surriel.com, kernel-team@meta.com Subject: Re: [PATCH v2 1/2] kexec: history: track previous kernel version Message-ID: References: <20260102-kho-v2-0-1747b1a3a1d6@debian.org> <20260102-kho-v2-1-1747b1a3a1d6@debian.org> <86secn7ors.fsf@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <86secn7ors.fsf@kernel.org> X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 5B978A000B X-Stat-Signature: huqhi8t9o3nj8p8tgjaozwj1rtpkwppz X-Rspam-User: X-HE-Tag: 1767610063-518031 X-HE-Meta: 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 dA1iFXTi AP54x+69Kxace+qVyUQbLP9T7bZfEkeEe79TPUJli2g6bdK6iK37TeBrek9frG8aEpY+jAMbzzo92uDRc955mT3RDqqa1JmJlvh7TOSfPzsONUHM0hciTK3UgghvBt469t+TxiaSqpwRvYrcaHGgfLR1GSZNmtNtjuxDmU4NG+7N3C0Y5EBajn2WVuohc9xziWVdoH35fip0d5lUJFoNZjZAcOVk36axI82r1QWktxw9WF96L9Ci4SvXt/oWmuv8plk4hkArHeEKE5EXttoGAZLEkbGSA4Z2R41LlRcMzyi0K3X1uQwlbuEn7ZQl/Tybq+K8Ulhem0NkRLaIVz6QHJavPItbt52I23svtZOb6bmZ0h3eQwxDZaCTEFIjrer5LarGaDgeg2ikdCiM4VUm9uDx98sYoppHmSnis X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello Pratyush, On Fri, Jan 02, 2026 at 09:17:27PM +0100, Pratyush Yadav wrote: > > Subject: [PATCH v2 1/2] kexec: history: track previous kernel version > > Nit: please use the prefix "kho: " for KHO patches. ack. > On Fri, Jan 02 2026, Breno Leitao wrote: > > Add CONFIG_KEXEC_HISTORY to store and display the kernel version from > > the previous kexec boot. > > > > When enabled, the current kernel's release string is saved to the > > "previous-release" property in the KHO device tree before kexec. On > > the next boot, if this property exists, the previous kernel version > > is retrieved and printed during early boot. > > > > This helps diagnose bugs that only manifest when kexecing from > > specific kernel versions, making it easier to correlate crashes with > > the kernel that initiated the kexec. > > Why can't you use journalctl to figure out which kernel was running > previously? This is a good question, this is why this doesn't work for me: 1) in some cases you cannot rely on systemd infrastructure. - This is very common when you have linux as the boot loader, which basically boot linux (UEFI -> Bootloader/linux -> kexec -> target linux) - In these cases, the bootloader doesn't have write access to the filesyste/journal - This is becoming more and more common. For instance, at Meta, Linux is the default bootloader. 2) in some of the bugs I've listed earlier, the machine doesn't even get to userspace before the crash. For instance, in the bug fixed by commit 77d48d39e991 ("efistub/tpm: Use ACPI reclaim memory for event log to avoid corruption"), the kernel was not reach userspace/init, thus, it would not be possible to run journalctl. Thanks for the review, --breno