From: Alistair Popple <apopple@nvidia.com>
To: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	catalin.marinas@arm.com, will@kernel.org, david@kernel.org,
	akpm@linux-foundation.org, Alistair Popple <apopple@nvidia.com>
Subject: [PATCH] arm64: mm: call pagetable dtor when freeing hot-removed page tables
Date: Thu, 21 May 2026 13:27:30 +1000	[thread overview]
Message-ID: <20260521032730.2104017-1-apopple@nvidia.com> (raw)

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().

Fixes: 5e8eb9aeeda3 ("arm64: mm: always call PTE/PMD ctor in __create_pgd_mapping()")
Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
 arch/arm64/mm/mmu.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 8e1d80a7033e..0c24fe650e95 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1422,6 +1422,7 @@ 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);
 }
 
-- 
2.54.0

next             reply	other threads:[~2026-05-21  3:27 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-05-21  3:27 Alistair Popple [this message]
2026-05-21 22:31 ` [PATCH] arm64: mm: call pagetable dtor when freeing hot-removed page tables Andrew Morton
2026-05-21 23:50   ` Alistair Popple
2026-05-22  7:15   ` Catalin Marinas
2026-05-22  7:32     ` Catalin Marinas
2026-05-22  9:36     ` Vishal Moola
2026-05-26 11:54       ` Kevin Brodsky
2026-05-26 12:31         ` David Hildenbrand (Arm)
2026-05-27  7:34           ` Kevin Brodsky
2026-05-27  9:22             ` Vishal Moola
2026-05-31 19:29             ` David Hildenbrand (Arm)
2026-05-26 15:07         ` Will Deacon
2026-05-27  7:35           ` Kevin Brodsky
2026-05-27  9:30             ` Vishal Moola
2026-05-28  8:05               ` Kevin Brodsky
2026-05-29 10:16                 ` Vishal Moola

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