On Mon, Nov 10, 2025 at 04:56:37PM -0500, Zi Yan wrote:

On 10 Nov 2025, at 16:16, Lorenzo Stoakes wrote:

quoted

OK ignore the past mail, I have managed to repro this locally and have a
fix.

Turns out the swap code is doing something quite insane... I will send
fix-patches to the series shortly.

Meanwhile I attach fix-patch! :)

Cheers, Lorenzo

----8<----
From c705fd85a806f53017df31e6b072c4bfa839e3a2 Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <redacted>
Date: Mon, 10 Nov 2025 21:11:52 +0000
Subject: [PATCH] fix

Signed-off-by: Lorenzo Stoakes <redacted>
---
 include/linux/leafops.h |  4 ++--
 mm/swapfile.c           | 12 ++++++++++--
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/include/linux/leafops.h b/include/linux/leafops.h
index a464a7e08c76..c4cd36760ea0 100644
--- a/include/linux/leafops.h
+++ b/include/linux/leafops.h

@@ -56,7 +56,7 @@ static inline softleaf_t softleaf_from_pte(pte_t pte)
 {
 	softleaf_t arch_entry;

-	if (pte_present(pte))
+	if (pte_present(pte) || pte_none(pte))
 		return softleaf_mk_none();

 	pte = pte_swp_clear_flags(pte);

@@ -95,7 +95,7 @@ static inline softleaf_t softleaf_from_pmd(pmd_t pmd)
 {
 	softleaf_t arch_entry;

-	if (pmd_present(pmd))
+	if (pmd_present(pmd) || pmd_none(pmd))
 		return softleaf_mk_none();

 	if (pmd_swp_soft_dirty(pmd))

diff --git a/mm/swapfile.c b/mm/swapfile.c
index fd23d9f7ae10..f0dcf261f652 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c

@@ -3202,9 +3202,17 @@ static int claim_swapfile(struct swap_info_struct *si, struct inode *inode)
  */
 unsigned long generic_max_swapfile_size(void)
 {
-	const softleaf_t entry = swp_entry(0, ~0UL);
+	softleaf_t entry = swp_entry(0, ~0UL);
+	const pte_t pte = softleaf_to_pte(entry);

-	return swp_offset(softleaf_from_pte(softleaf_to_pte(entry))) + 1;
+	/*
+	* Since the PTE can be an invalid swap entry (i.e. the none PTE), we do

So softleaf_from_pte() returns softleaf_mk_none() instead and causes the
issue?

Yup :) fun!

It's kinda crazy that on x86-64 at least we _intentionally_ generate an invalid
swap entry but there we go.

quoted

+	* this manually.
+	*/

This comment is not aligned, in case you plan to send this patch as is. :)

Lol ugh, well I've split out this fix with fixes for all other raised points and
plan to send a v3 of that series to make life easier.

There's a bunch of conflicts that arise from the changes so that's easier for
everyone.

quoted

+	entry = __pte_to_swp_entry(pte);
+	entry = swp_entry(__swp_type(entry), __swp_offset(entry));
+
+	return swp_offset(entry) + 1;
 }

 /* Can be overridden by an architecture for additional checks. */
--
2.51.0

This fix looks good to me. Thanks.

Thanks!

Best Regards,
Yan, Zi

Cheers, Lorenzo