From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 93DDDC55822 for ; Wed, 5 Aug 2026 05:58:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=v7zCWK++jNfxfhEt8Y8jIgML8WXQN15ZQy6uHyDnBnc=; b=RNxkIq6JTLrzoMm21G3EWFdQQw t7Aj/LMj9w9MEgx3tQt9O4uD0QLTjKLB34r+atl6/YLDwrhQkoID1TsruYfGcn3waw2mlHLXt6F82 66Q4fcGunsYt9X4UtlQpxW+nSxFxaDdE+zpvuGyJ5Y+KSDPLZsOjb/FKmqgO+M5P0YHF2fWC/Zfr5 nv+WCnvy+4FWeQf9/UJWgnzyuBCb+yQsb3EbzUG3e69VglsnAWZIbODnY7k2gRS/TAXNhF/vrl/+p lB7xw+68kJoEXAuUIZzoLhHkuIDvGNbnO5NU4nMZ+QDdyBltNIzy0z+Fs1jz8D+hSMHncSTD5YozF ZHgNJJYw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wrUdo-00000003H5j-0IeW; Wed, 05 Aug 2026 05:58:12 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wrUdn-00000003H5P-16rk for linux-arm-kernel@lists.infradead.org; Wed, 05 Aug 2026 05:58:11 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 12245403D2; Wed, 5 Aug 2026 05:58:10 +0000 (UTC) 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 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 X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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