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 E62C4395ACD; Fri, 9 Oct 2026 20:43:11 +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=1791578592; cv=none; b=qkpToV6nDzq1StQ86GYV8SXxgoO3rerwAAtcpVvZQWzmxmH9r+JXTA+nD3Xiq2PepOe2kdUbYDpvOXXakT73Nibche2NG5fG5iYKDfOmmAxzSDCJcFx3I1VTDQkUMgcEuIWEw2xWI/6vxj9ctcUBnw7hnjszqwZZtm6r0Mpg0JA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791578592; c=relaxed/simple; bh=N6FjwFwOZG1eWNtQeKvq39djVLP7i9vN+zdPlsY+4hk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=WuyQt5Ht00HqUn7zh2RIVU766N2Ziji7TZjDLvsHMU/nVUeVBUs4lxb4Sh8JRFF6YK6BmfXqDwH4vWaRoVP+f0bFFc/V3uMP9c9Gg7qS4IXPQxtGSzjoKRzfgJ74be+1yxPmp5AAFtRYoMBKJktODKmgtdtWEgmOGlJQI2qMbFA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SP23AZs/; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SP23AZs/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CEA6F1F000FF; Fri, 9 Oct 2026 20:43:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791578591; bh=JxCU4kgy6yuLL3vMKMbNFEILfGTC3AEpOEg/HFNIu60=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=SP23AZs/ZMLS1F7HAiY5z7X5nF2RAOysCWRarEHnTfxNiZ6ItX8IcZVYkiT3Xyrzw Ts27Z3REnfSbgPcmeCHEvXQfI5R0zszY/WgI7oNDs5Uuk4RtQelzpmDtOVb/O1mgbC ESJ+fGuVP07bnVnyI4wWN+oqUM/udZKJQpOIxZ7jC0KEakCwnj/veq68QxurhH1xPa x4QNtZRPeZ9Z9OSE+fx43CSrHusaCl/LHAxjU2JLx+s5fnC628xxa9yw0FVkBWzqfI F/V/SeQf2YozHcliqBqzshsNtBivlYnNq0VSVj9gwdZur95pXceUhTxA42KBjet0PE DuKW2pGkIo/aQ== Message-ID: Date: Fri, 9 Oct 2026 22:43:02 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/4] arm64/mm: fix destructor for unconstructed hotplug page tables To: Muchun Song , akpm@linux-foundation.org Cc: linux-mm@kvack.org, stable@vger.kernel.org, osalvador@suse.de, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, linux-arm-kernel@lists.infradead.org, pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, linux-riscv@lists.infradead.org, agordeev@linux.ibm.com, kevin.brodsky@arm.com, bjorn@rivosinc.com, apopple@nvidia.com, linux-kernel@vger.kernel.org, muchun.song@linux.dev References: <20261008073021.2512665-1-songmuchun@bytedance.com> <20261008073021.2512665-5-songmuchun@bytedance.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/8/26 09:30, Muchun Song wrote: > Commit c594b83457cc ("arm64: mm: call pagetable dtor when freeing > hot-removed page tables") made free_hotplug_pgtable_page() > unconditionally run the page-table destructor. This matches page tables > allocated by the arm64 mapping code, which runs the corresponding > constructors. > > However, arm64 also uses the generic sparse-vmemmap population code. > Runtime intermediate page tables allocated by that code do not run a > page-table constructor. Why do we have that inconsistency? It seems to cause pain :) > Freeing one during memory hot-remove therefore > runs a destructor without a matching constructor and corrupts > NR_PAGETABLE accounting. > > Use PageTable() to run the destructor only for page-table pages whose > constructor initialized them. This keeps the arm64-created page-table > lifecycle balanced while safely freeing constructor-free vmemmap tables. > > Fixes: c594b83457cc ("arm64: mm: call pagetable dtor when freeing hot-removed page tables") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Muchun Song > --- > arch/arm64/mm/mmu.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 7343ac9294f8..688b33095651 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -1495,7 +1495,8 @@ 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)); > + if (PageTable(page)) > + pagetable_dtor(page_ptdesc(page)); > free_hotplug_page_range(page, PAGE_SIZE, NULL); That results in a __free_pages() for ones allocated by sparse-vmemmap population code. Are we sure that's the right thing to do? This is all so inconsistent and confusing :( -- Cheers, David