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 AF62616DC28 for ; Thu, 21 May 2026 22:31:31 +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=1779402692; cv=none; b=FBmNboRz54aZIaOSty29GsUZag8v6+rEOjPUG3BqDCTxSx+k2vNJdjZWAxiSm3++NHQuSB7JtJXHi17mEnfMag1mqP9El4iIX6L67E+y6I9AHdNK8Ej1vbOYkljW3luQN/UlVg3WskQZRZVzWzS/IfqWKSiWhj59/w9iWVCa294= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779402692; c=relaxed/simple; bh=INVM/aEAix0VnWuxABkyIwXGb/l+lcza/+8nbqVmBuw=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=oKE77Fvel+ANow2C/ldD+SCW8kbb4GRr1wJtJytRSdX/33cgz0zM2iuKbNgNwatw+vlemY7xCT8xxvEcEfes4fcXRcLOD3IMBDIeWZF0AgEAzOljdhutTHEsdEOizFxUdeu7l9yU9dJCuHVDZ3Rfixd0zH1ny/dicz34bw+ygCI= 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=dgyXsqH6; 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="dgyXsqH6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F02621F000E9; Thu, 21 May 2026 22:31:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1779402691; bh=bnv8z/U53fPYRQVRdESTD0xQjxqDX0NyGk7FJvl1zug=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=dgyXsqH67FvyK+9N+RrmIuzBnPicK5E+nVD175qTBrUi/dZfe//hrorWytuL6wRpo g/WQLOOXYW9aoOx0MAwfabDfx6fXjkFvdm7PbfxgdHHnL9fSY4y2XNQ7fJZips1O8Q NBQBE0pdjLnBhjrbbOTs7Jlfa8pXiZwDxcbAiEq0= Date: Thu, 21 May 2026 15:31:30 -0700 From: Andrew Morton To: Alistair Popple Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, catalin.marinas@arm.com, will@kernel.org, david@kernel.org Subject: Re: [PATCH] arm64: mm: call pagetable dtor when freeing hot-removed page tables Message-Id: <20260521153130.d7d5cd060f7522f894252333@linux-foundation.org> In-Reply-To: <20260521032730.2104017-1-apopple@nvidia.com> References: <20260521032730.2104017-1-apopple@nvidia.com> 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 Thu, 21 May 2026 13:27:30 +1000 Alistair Popple wrote: > 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()") 6.16+, so I assume we want cc:stable here. > 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); > } 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.