From: Andrew Morton <akpm@linux-foundation•org>
To: Catalin Marinas <catalin.marinas@arm•com>
Cc: Alistair Popple <apopple@nvidia•com>,
linux-arm-kernel@lists•infradead.org,
linux-kernel@vger•kernel.org, linux-mm@kvack•org,
will@kernel•org, david@kernel•org
Subject: Re: [PATCH] arm64: mm: call pagetable dtor when freeing hot-removed page tables
Date: Mon, 1 Jun 2026 21:22:25 -0700 [thread overview]
Message-ID: <20260601212225.11f277a85d5ed15083b08cc2@linux-foundation.org> (raw)
In-Reply-To: <ahACfQ6kCfONqz5h@arm.com>
On Fri, 22 May 2026 08:15:09 +0100 Catalin Marinas <catalin.marinas@arm•com> wrote:
> > > --- 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);
> > > }
> >
> > I'd of course prefer that arm maintainers handle this. But
> > 5e8eb9aeeda3 came via myself so convention kinda-dictates that I get to
> > fix it.
>
> That's fine but Sashiko has some points:
>
> https://sashiko.dev/#/patchset/20260521032730.2104017-1-apopple@nvidia.com
>
> The __remove_pgd_mapping() path is fine but we also have the
> vmemmap_free() path where the constructor was never called.
>
> We could pass around a bool dtor argument but I wonder whether we could
> just check it's a pgtable page:
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 4c8959153ac4..9d42cbddce27 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1441,6 +1441,9 @@ static void free_hotplug_page_range(struct page *page, size_t size,
>
> static void free_hotplug_pgtable_page(struct page *page)
> {
> + if (folio_test_pgtable(page_folio(page)))
> + pagetable_dtor(page_ptdesc(page));
> +
> free_hotplug_page_range(page, PAGE_SIZE, NULL);
> }
This patch is still floating around in mm.git awaiting some
finalization. What to do?
From: Alistair Popple <apopple@nvidia•com>
Subject: arm64: mm: call pagetable dtor when freeing hot-removed page tables
Date: Thu, 21 May 2026 13:27:30 +1000
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>
---
arch/arm64/mm/mmu.c | 1 +
1 file changed, 1 insertion(+)
--- a/arch/arm64/mm/mmu.c~arm64-mm-call-pagetable-dtor-when-freeing-hot-removed-page-tables
+++ a/arch/arm64/mm/mmu.c
@@ -1441,6 +1441,7 @@ static void free_hotplug_page_range(stru
static void free_hotplug_pgtable_page(struct page *page)
{
+ pagetable_dtor(page_ptdesc(page));
free_hotplug_page_range(page, PAGE_SIZE, NULL);
}
_
next prev parent reply other threads:[~2026-06-02 4:22 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-21 3:27 [PATCH] arm64: mm: call pagetable dtor when freeing hot-removed page tables Alistair Popple
2026-05-21 22:31 ` 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
2026-06-02 4:22 ` Andrew Morton [this message]
2026-06-02 13:12 ` Will Deacon
2026-06-02 17:06 ` Andrew Morton
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