From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A2B0633BBCC for ; Tue, 2 Jun 2026 04:22:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780374147; cv=none; b=rJkabGAuVhF3ujINl9+0bs5nJwW5WXT4f0s16JJjq1Ts7qF9PI1BqgtObcWS+FBsVmj1kpOzWYK5uDz7hOr3yqeSoTchpJLm4WqNlXohAeqBPC586GAcVw5r7wi69pdV3UACftmDXjH5QilUOooMQ8nGScsVVQcK2dPESGNdxGE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780374147; c=relaxed/simple; bh=mOWXWcMCcJSK6DsKwme0YP9vbhxiWH+Qws8uDkWRNeY=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=qv5Wwljpuy0gWTNgW+o/skxQqhqDeHdWDlw2pOdvD55Uw9DwwdrkTzsV9bST1Apix9j3Ed9dmA0oAy0Q2MY+7IjpGcijMrZP3g/BI/Jog1Cj09YiO3a4aTW+ZS4oHqIgn4a+lxortZ1+si5otUqH5p2puLqlsFPwKCplo7KXDQQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=SeRc4CB3; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="SeRc4CB3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 285571F00893; Tue, 2 Jun 2026 04:22:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1780374146; bh=nXGOCPORwRtBIOtgSlL5BmqNdJWalyZfji2BLv/IMKg=; h=Date:From:To:Cc:Subject:In-Reply-To:References; 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) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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); } _