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 6250E3403E8; Wed, 5 Aug 2026 05:58:10 +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=1785909491; cv=none; b=kx1CNYjaqFANVatDbUB1UAks0JjEIp3I/haqaIpT7A6WDIKjOvklIsEvYKftY0tNE1FD7f450O+54vZZS8Ti3IIwePBVl/V+PCghN1BGXVM71lWZ0wrwMkO350s2rK8nOR2kwgAdIWXf9nvIzyV2GI5xExJzh69ZgD2cqFE2X4M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785909491; c=relaxed/simple; bh=05r7tS7FwUKD/e4NnomclcLpuPqMIKhQGaOK/mPLxWI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Yd2amsJXl1jCscPKOPBk8Cc6v7/BtZ6mz0fSfF+OpEeiU8tbHyziZYapnWK3B3DVJ2BEX09iDWKuQ9ShzobGcDll00VLeg+Hi2HVnnol4MV1wsL9JfnSgaP10bUH5OPfSQQ6P3aAo5tJ1MxMlab/Bgf1Yfr2fJJj3ReA/jkDQIQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WpTfVY+g; 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="WpTfVY+g" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 574631F000E9; Wed, 5 Aug 2026 05:58:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785909490; bh=v7zCWK++jNfxfhEt8Y8jIgML8WXQN15ZQy6uHyDnBnc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=WpTfVY+gis0GaZ8Ilij2iuNXtip1yECYuuQNUlYVo6jVc87VSMT30kmNOwPl/ZTao 7oJbpElLKRYZM/H9E3uzPA0m2dDs7qxBrWfUSWeNQgVusyFJAB0zhgsb3CndB3eLBl oVx+8kJVKo/dvCnEjFd77EC7hbxP5rQoI682riTb93MQ9TfiRSWCb3g5JOckn0oZli 58e+xTR7r2M3llPSRy5MrzI9rSBdgu2K2JYrZI3FiSOydblbfVLAtbSKgrhbcozdEM SIQIBRN5owC9lJ1/5UdzSc5P9So3/Y8YL+DvqEaETnFE51wJndUFjamNuiFbFR2lzb lLGJvpl87Db5A== Message-ID: <595fe323-59d3-4f4a-92a3-ac5d67b7461b@kernel.org> Date: Wed, 5 Aug 2026 07:58:02 +0200 Precedence: bulk X-Mailing-List: linux-parisc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 6/6] mm: constify the pte_offset_map_ro_nolock() return value To: Pedro Falcato , "Lorenzo Stoakes (ARM)" Cc: David Hildenbrand , Andrew Morton , Catalin Marinas , Will Deacon , "James E.J. Bottomley" , Helge Deller , Madhavan Srinivasan , Michael Ellerman , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kevin Brodsky , Muhammad Usama Anjum , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org References: <20260803164400.531199-1-pfalcato@suse.de> <20260803164400.531199-7-pfalcato@suse.de> Content-Language: fr-FR From: "Christophe Leroy (CS GROUP)" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Le 04/08/2026 à 21:22, Pedro Falcato a écrit : > On Tue, Aug 04, 2026 at 12:22:19PM +0100, Lorenzo Stoakes (ARM) wrote: > >> >>> if (!pte) { >>> mmap_read_unlock(mm); >>> result = SCAN_NO_PTE_TABLE; >>> diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c >>> index b91b1a98029c..2cfc6e608ef4 100644 >>> --- a/mm/pgtable-generic.c >>> +++ b/mm/pgtable-generic.c >>> @@ -308,8 +308,8 @@ pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp) >>> return NULL; >>> } >>> >>> -pte_t *pte_offset_map_ro_nolock(struct mm_struct *mm, pmd_t *pmd, >>> - unsigned long addr, spinlock_t **ptlp) >>> +const pte_t *pte_offset_map_ro_nolock(struct mm_struct *mm, pmd_t *pmd, >> >> Can pmd be const too? > > I was going to say "yes but then pmdp_get() also needs to be constfified" but > actually no, it can't: > > pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp) { > if (unlikely(pmd_bad(pmdval))) { > pmd_clear_bad(pmd); > goto nomap; > } > } > > so PTE mapping actually needs to write to the pmdp if the pmd looks bad. > Tricky stuff :) But if pmd is const, can it be bad at all ? Christophe