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b=SeRc4CB3tfoKRBhIV6CGSKRkthW7QoclBiBsZUpKUThMOsXOQD8ty6QdCV0U8iGvs qb9WbjKCfWAijL1XQoR2zdLBhNf8zE90wk4B7r+Vg1SkFv/MvZPhepzVtpqXtRVNPB IjhNm2dPXy3wlmsU+kVOfZzq6mhQwdo4CryaCDdo= Date: Mon, 1 Jun 2026 21:22:25 -0700 From: Andrew Morton To: Catalin Marinas Cc: Alistair Popple , 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 Message-Id: <20260601212225.11f277a85d5ed15083b08cc2@linux-foundation.org> In-Reply-To: References: <20260521032730.2104017-1-apopple@nvidia.com> <20260521153130.d7d5cd060f7522f894252333@linux-foundation.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 46C14C0004 X-Stat-Signature: 6qgjuma1jb48oyzp4i4xn1aj1giekbrm X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1780374147-696574 X-HE-Meta: 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 RcvboRvK EXvJkh/JzYLA1MluIa7ecAYb3KIajxOYqV34d3m4yywr3pHL+rj6sdkb/6Ora1D1pjPLNd4+4kx0GIrKb6LeMsKCU5NSVPrqWbMvSPlmvczH6a/6kN+38uEm0R4mlqitvSln4ktpNKc5gJdHvHd+Y2B/aTNRxGqAgGEfhI8pIwhWSDmwu0rRPDDYu8hqKrQLuNLFH/11P8dwc4BRPA7kE9L/JbvULAUwOLEGtC1sCpVsRX84AfdbUgPdfMa6WoDG88vdjXh9lGemVkid4Kvkqws4Rk7SkOVb9lM1XweRvAnRa3Iyiz7dT9cTAXrU+drloLeiugRSJn7ZWtoewOw9QKbPGI4Xnguwcvfa5qJGjdT3/39IwINwfyFpZOVW9Kg1ymqtECcAlzZpMnX3oPJ3hxt4PkoB4vZ9s9B/GBYOM9Zkos1Y5OvdqzjWiZTLm7VenGpanWYpXigMHAOtOyDooSIx4Cg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 22 May 2026 08:15:09 +0100 Catalin Marinas 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 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 Cc: Catalin Marinas Cc: David Hildenbrand Cc: Will Deacon Cc: Signed-off-by: Andrew Morton --- 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); } _