From: Alistair Popple <apopple@nvidia.com>
Date: Thu, 21 May 2026 03:27:30 +0000 (+1000)
Subject: arm64: mm: call pagetable dtor when freeing hot-removed page tables
X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=c594b83457ccdee76d458416fb3bc9348a37592f;p=thirdparty%2Fkernel%2Flinux.git

arm64: mm: call pagetable dtor when freeing hot-removed page tables

Since 5e8eb9aeeda3 ("arm64: mm: always call PTE/PMD ctor in
__create_pgd_mapping()") page-table allocation on ARM64 always calls
pagetable_{pte,pmd,pud,p4d}_ctor().  This sets the page_type to
PGTY_table, increments NR_PAGETABLE and possible allocates a PTL.  However
the matching pagetable_dtor() calls were never added.

With DEBUG_VM enabled on kernel versions prior to v6.17 without
2dfcd1608f3a9 ("mm/page_alloc: let page freeing clear any set page type")
this leads to the following warning when freeing these pages due to
page->page_type sharing page->_mapcount:

  BUG: Bad page state in process ... pfn:284fbb
  page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x284fbb
  flags: 0x17fffc000000000(node=0|zone=2|lastcpupid=0x1ffff)
  page_type: f2(table)
  page dumped because: nonzero mapcount
  Call trace:
   bad_page+0x13c/0x160
   __free_frozen_pages+0x6cc/0x860
   ___free_pages+0xf4/0x180
   free_pages+0x54/0x80
   free_hotplug_page_range.part.0+0x58/0x90
   free_empty_tables+0x438/0x500
   __remove_pgd_mapping.constprop.0+0x60/0xa8
   arch_remove_memory+0x48/0x80
   try_remove_memory+0x158/0x1d8
   offline_and_remove_memory+0x138/0x180

It can also lead to leaking the ptl allocation if ALLOC_SPLIT_PTLOCKS is
defined and incorrect NR_PAGETABLE stats.  Fix this by calling
pagetable_dtor() in free_hotplug_pgtable_page() prior to freeing the page
to undo the effects of calling pagetable_*_ctor().

Link: https://lore.kernel.org/20260521032730.2104017-1-apopple@nvidia.com
Fixes: 5e8eb9aeeda3 ("arm64: mm: always call PTE/PMD ctor in __create_pgd_mapping()")
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index dd85e093ffdb1..8242f93f05e4f 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1441,6 +1441,7 @@ static void free_hotplug_page_range(struct page *page, size_t size,
 
 static void free_hotplug_pgtable_page(struct page *page)
 {
+	pagetable_dtor(page_ptdesc(page));
 	free_hotplug_page_range(page, PAGE_SIZE, NULL);
 }