linux-kernel - Re: [PATCH v4] kho: kexec-metadata: track previous kernel chain

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Message-ID: <aXdGyXNUO0mPwJsp@gmail.com>
Date: Mon, 26 Jan 2026 02:51:58 -0800
From: Breno Leitao <leitao@...ian.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: Alexander Graf <graf@...zon.com>, 
	Pasha Tatashin <pasha.tatashin@...een.com>, 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, SeongJae Park <sj@...nel.org>
Subject: Re: [PATCH v4] kho: kexec-metadata: track previous kernel chain

On Sun, Jan 25, 2026 at 01:32:27PM +0200, Mike Rapoport wrote:
> On Thu, Jan 22, 2026 at 04:04:55AM -0800, Breno Leitao wrote:
> > Ack! I am planning something as:
> > 
> > 	commit 90e098ca0d611b44594f08e50ba1cff3c932dd2b
> > 	Author: Breno Leitao <leitao@...ian.org>
> > 	Date:   Thu Jan 22 03:47:23 2026 -0800
> > 
> > 	kho: document kexec-metadata tracking feature

...

> I'd move this section before "debugfs Interfaces", other than that LGTM.

Ack!

> > > Can't we move it into the existing if (fdt) below?
> > 
> > Unfortunately, that won't work due to a data dependency between the two
> > functions.
> > 
> > kho_process_kexec_metadata() reads from the FDT subtree and populates kho_in:
> > 
> > Basically:
> > 
> > 	kho_in.kexec_count = metadata->kexec_count;
> > 
> > While kho_populate_kexec_metadata() increments metadata->kexec_count:
> > 
> >           /* kho_in.kexec_count is set to 0 on cold boot */
> >           metadata->kexec_count = kho_in.kexec_count + 1;
> > 
> > If kho_process_kexec_metadata() is moved after kho_populate_kexec_metadata(),
> > the count would always increment from 0 to 1, ignoring whatever was passed in
> > the FDT.
> > 
> > Restructuring to call kho_in_debugfs_init() earlier also doesn't work:
> > 
> > 
> > 	if (fdt) {
> > 		kho_in_debugfs_init(&kho_in.dbg, fdt);
> > 		kho_process_kexec_metadata();
> > 		return 0;
> > 	}
> > 
> > 	/* Populate kexec metadata for the possible next kexec */
> > 	err = kho_populate_kexec_metadata();
> > 	if (err)
> >                   pr_warn("failed to initialize kexec-metadata subtree: %d\n",
> >                           err);
> > 
> > This would return early without populating the kexec metadata for the next
> > kexec, breaking the chain on KHO boots.
> 
> How about we rename kho_process_kexec_metadata() to
> kho_retreive_kexec_metadata() and add kho_process_kexec_metadata() that
> will first call _retrieve and then _populate? Something like
> 
> static int __init kho_process_kexec_metadata(const void *fdt)
> {
> 	int err;
> 
> 	if (fdt)
> 		kho_retrieve_kexec_metadata();
> 
> 	/* Populate kexec metadata for the possible next kexec */
> 	err = kho_populate_kexec_metadata();
> 	if (err)
> 		pr_warn("failed to initialize kexec-metadata subtree: %d\n",
> 			err);
> 
> 	return err;
> }

That would work, I will probably rename it to kho_kexec_metadata_init()
or kho_kexec_metadata_setup() to follow the same pattern already there.

Thanks for the review, I will send an updated version soon,
--breno