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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id BEE66C88E72 for ; Thu, 17 Sep 2026 09:48:33 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id ACE276B009B; Thu, 17 Sep 2026 05:48:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A58586B009D; Thu, 17 Sep 2026 05:48:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 91FCA6B009E; Thu, 17 Sep 2026 05:48:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 66F316B009B for ; Thu, 17 Sep 2026 05:48:32 -0400 (EDT) Received: from smtpin07.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 9266D1C1F2F for ; Thu, 17 Sep 2026 09:48:31 +0000 (UTC) X-FDA: 85222779222.07.AB68C3A Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf28.hostedemail.com (Postfix) with ESMTP id 0EE94C0008 for ; Thu, 17 Sep 2026 09:48:29 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=RXQbRdQb; spf=pass (imf28.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1789638510; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=SSQlyaKBFOXmjTXXwb4CnAc04mzkW2ufkK1lWWnGyPE=; b=Eum7QnTCy5pJY06DbBcjVKCwRze8GB0Yxhw4siwU3EGiukMfixgemTMUPJdcWEyYuLKJLV zjrCcqNP8IgtSg7m2iDAhi1qMVwzNpQu6axV+0C185B/CQ7bL64wtB9h5+kQOZdGHrXLZi 7k2pNRJRH/PmTEwMpqNhs/F1Q6L7iVQ= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=RXQbRdQb; spf=pass (imf28.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1789638510; b=WkIHSDohtq0uAxnn0txJSQ1yy2lb9VxptVlx1LJM93UAgBhq8zomQoX1o0AhF/MIAZY/j+ 2/sWxKKRX5G/3+NntRq1yqGCyNGt/+cqEiWAn79RNQpMLPj2lBX2FG96oIwXrHhnjpW2BS YFT0+hJuF18E1lifkGfBSYt0vDWpm7w= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 8C2CB600D4; Thu, 17 Sep 2026 09:48:29 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A58101F000FF; Thu, 17 Sep 2026 09:48:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789638509; bh=SSQlyaKBFOXmjTXXwb4CnAc04mzkW2ufkK1lWWnGyPE=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=RXQbRdQbaMBgU589o6W6PG3uphqN8mz/5BLM7kb4FOOK2HUFAR93FxbAoJTEAO8Bu eBoMaio317U16mMAW0vaD84KGV27INu10hhQohZWaKuKgfSOO3qZzptjmllqY/CUt/ IuuDdJMQ0mKaF3URDpMUpD2v9wmA5TOXdERqKfg6G4aBNbU+E4K218mD0RumAFV1Mt COnZBQ1CMqCB/u9P+dkXryFycmkanLLTAJtGqNyQEtHTufZKXMU081Bw99vgtS9b0W qM4li9bj33ALeGiPbwdYhg9T2fzZ9DGvn14y4LfOgNz2xVrwZu3cOup4lJ6KfrLH9o JwkgKTsO8Aq7Q== Date: Thu, 17 Sep 2026 10:48:17 +0100 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: Kiryl Shutsemau , Andrew Morton , Suren Baghdasaryan , "Liam R. Howlett" , Vlastimil Babka , Shakeel Butt , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Mike Rapoport , Michal Hocko , Xu Xin , Chengming Zhou , Jann Horn , Pedro Falcato , Rik van Riel , Harry Yoo , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park , Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Guilherme Giacomo Simoes Subject: Re: [PATCH v2] mm: implement and use vma_anon_tracked(), silence KCSAN Message-ID: References: <20260910-vma-is-faulted-v2-1-e81ebc7d146b@kernel.org> <4b2c99f6-d7c0-42a2-bf9a-e85061d53c93@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4b2c99f6-d7c0-42a2-bf9a-e85061d53c93@kernel.org> X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 0EE94C0008 X-Stat-Signature: kjwjw66z6be9px91q5944tczajo3otgk X-Rspam-User: X-HE-Tag: 1789638509-35879 X-HE-Meta: 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 6DjU1lN8 eIgKP+SpzyYFs8s10dj9XqdK+tHVUJBmv+RBl231DnRBEgCDYbJYgMwJjUFNIgB1EhfVUaMT528dsIU6D6P/UIODdB4SEIgAHaCgeoDjmJESIR7wqOeH1c67lCNUbbVJIOtOHiHRKKAQc6d53A8QYkK2sxBO/DIG8kNGpBmBIlc75t2OrfmyVot+DEb+tfo4Jjfbt+4YaYjCgPnOS/vidBMONsLS3ZVWpLJu2tV7M/CXjjTLNaGyKxU4O3tJZLqthhhHAno9PPWNJMCh4+Y/PgbUqTbaN5ROGzylKXkIFvzDvSCTt+UBXsfuAIalhW+OFRFxHMcM798hhCo+4sm4fgM+nqA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Sep 17, 2026 at 11:45:12AM +0200, David Hildenbrand (Arm) wrote: > On 9/14/26 17:21, Lorenzo Stoakes (ARM) wrote: > > On Thu, Sep 10, 2026 at 02:50:25PM +0100, Kiryl Shutsemau wrote: > >> On Thu, Sep 10, 2026 at 02:18:35PM +0100, Lorenzo Stoakes (ARM) wrote: > >>> Provide a function to abstract the common task of checking whether > >>> a VMA is faulted in or not. > >>> > >>> A VMA or mmap lock must be held when calling this function. For an attached > >>> VMA the transitions between unfaulted/faulted state are: > >>> > >>> Transition | VMA/mmap Lock state > >>> ------------------------|----------------------------------------------- > >>> unfaulted to faulted | write lock OR read lock + mm->page_table_lock > >>> faulted to unfaulted | write lock > >>> > >>> So vma_anon_tracked() never provides a false positive (the lock precludes > >>> it), but if only a read lock is held, a negative result must be re-checked > >>> with mm->page_table_lock held. > >>> > >>> Detached VMAs cannot be concurrently manipulated as they are removed from > >>> the maple tree so require no guarantees. > >>> > >>> Use data_race() to silence KCSAN about non-existent data races between > >>> concurrent vma->anon_vma read/write on optimistic fault tests. > >>> > >>> Also while here, const-ify vma_is_attached(), vma_assert_stabilised() and > >>> dependants. > >> > >> If you end up respinning anyway, this would be a natural separate > >> prep patch. > > > > Yup will do, Pedro also asked for this! > > > >> > >>> Finally, update the core VMA merge/split, rmap, mremap, KSM and fault > >>> preparation callers which test vma->anon_vma directly to use > >>> vma_anon_tracked() instead. > >>> > >>> Note that the lockless read in reusable_anon_vma() is doing more than > >>> checking whether the VMA is faulted - it is returning the anon_vma to be > >>> used on fault, so this check is not altered. > >>> > >>> There is one odd one out - file_backed_vma_is_retractable() - which holds > >>> neither a VMA nor mmap lock and is stabilised by the file rmap lock only. > >>> > >>> Therefore just add a comment to explain why the direct vma->anon_vma check > >>> is required. > >>> > >>> Reported-by: Guilherme Giacomo Simoes > >>> Closes: https://lore.kernel.org/all/20260829100034.423064-1-trintaeoitogc@gmail.com/ > >>> Closes: https://lore.kernel.org/all/20260909115723.528501-1-trintaeoitogc@gmail.com/ > >>> Signed-off-by: Lorenzo Stoakes (ARM) > >>> --- > >>> v2: > >>> - Renamed vma_is_faulted() to vma_anon_tracked() as per David. > >> > >> I don't particularly like vma_anon_tracked(), but naming is hard... > > > > Yeah it was a compromise because David and I disagreed on naming (again ;) > > > > I think vma_has_anon_rmap() is a better compromise? > > Yeah let's go for that. Ack will do thanks! > > -- > Cheers, > > David -- Cheers, Lorenzo