+ mm-hugetlb-keep-max_huge_pages-when-dissolving-surplus-folios.patch added to mm-hotfixes-unstable branch

+ mm-hugetlb-keep-max_huge_pages-when-dissolving-surplus-folios.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/hugetlb: keep max_huge_pages when dissolving surplus folios
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-hugetlb-keep-max_huge_pages-when-dissolving-surplus-folios.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-keep-max_huge_pages-when-dissolving-surplus-folios.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Longlong Xia <xialonglong@kylinos.cn>
Subject: mm/hugetlb: keep max_huge_pages when dissolving surplus folios
Date: Fri, 14 Aug 2026 16:30:27 +0800

dissolve_free_hugetlb_folio() can remove a free folio as surplus when its
node has surplus pages.  In that case remove_hugetlb_folio() decrements
both nr_huge_pages and surplus_huge_pages, leaving the persistent pool
size unchanged.

Updating max_huge_pages as if a persistent folio had been removed can
therefore corrupt the persistent pool target and underflow it when
max_huge_pages is zero.  Keep max_huge_pages unchanged for surplus folios,
including the vmemmap restoration rollback path.

Link: https://lore.kernel.org/20260814083027.1419487-1-xialonglong2025@163.com
Fixes: cb402bbdabca ("mm/hugetlb: fix surplus pages in dissolve_free_huge_page()")
Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Longlong Xia <xialonglong@kylinos.cn>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jinjiang Tu <tujinjiang@huawei.com>
Cc: Longlong Xia <xialonglong@kylinos.cn>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlb-keep-max_huge_pages-when-dissolving-surplus-folios
+++ a/mm/hugetlb.c
@@ -2002,7 +2002,8 @@ retry:
 		if (h->surplus_huge_pages_node[folio_nid(folio)])
 			adjust_surplus = true;
 		remove_hugetlb_folio(h, folio, adjust_surplus);
-		h->max_huge_pages--;
+		if (!adjust_surplus)
+			h->max_huge_pages--;
 		spin_unlock_irq(&hugetlb_lock);
 
 		/*
@@ -2022,7 +2023,8 @@ retry:
 			if (rc) {
 				spin_lock_irq(&hugetlb_lock);
 				add_hugetlb_folio(h, folio, adjust_surplus);
-				h->max_huge_pages++;
+				if (!adjust_surplus)
+					h->max_huge_pages++;
 				goto out;
 			}
 		} else {
_

Patches currently in -mm which might be from xialonglong@kylinos.cn are

mm-hugetlb-keep-max_huge_pages-when-dissolving-surplus-folios.patch
mm-ksm-avoid-missing-ksmd-wakeups-in-ksm_enter.patch
zram-fix-out-of-bounds-access-in-writeback_store.patch
zram-fix-out-of-bounds-access-in-read_block_state.patch
zsmalloc-account-for-handle-size-in-class-lookup.patch