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

[Alistair Popple]

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 at 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