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 D080CC88E72 for ; Mon, 14 Sep 2026 15:21:59 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EC0856B00A3; Mon, 14 Sep 2026 11:21:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E70636B00BB; Mon, 14 Sep 2026 11:21:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D39396B00BC; Mon, 14 Sep 2026 11:21:58 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 6E0436B00A3 for ; Mon, 14 Sep 2026 11:21:58 -0400 (EDT) Received: from smtpin20.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id CCD3A401A1 for ; Mon, 14 Sep 2026 15:21:57 +0000 (UTC) X-FDA: 85212733074.20.9397078 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf10.hostedemail.com (Postfix) with ESMTP id 28426C0011 for ; Mon, 14 Sep 2026 15:21:56 +0000 (UTC) Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=HXLwSMkG; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf10.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1789399316; 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=BbM/6KmbIwqEmYkcORDjoWrwHW3qkC0k639i+OR+Sr8=; b=XVVibRfQkijHR461arczmZIha/TNlruXgnoc096hlwSaioWRClAiqlOVZmB5Q0f+x/iSRO JxIroqQVdxuXW8Q6Z6Q7Do2dynHdIgi1IyFea+8t2RPAw+5IQl5gOQAhLO6j/SAcA35LEC bdkoCp78Z/oUEUb0mK2K0tiJRDh9+Ww= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1789399316; b=sfFlq28DrIE/dDcf24OqM7fByV8msN38+kLE0J0DvZQvbv2XWGzTil66jSLSC9HbLqEWd1 nKcqB7y//q3Wmb2nzFrQg6+Og5MeTFZmZfU2PwjWow7RNPuR4OT0AeovGMEi5urOrjxi6u 5fcaPS99N3ulfVfUyaey+gDl7z+QNLE= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=HXLwSMkG; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf10.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 5B393415B7; Mon, 14 Sep 2026 15:21:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 504B41F000FF; Mon, 14 Sep 2026 15:21:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789399315; bh=BbM/6KmbIwqEmYkcORDjoWrwHW3qkC0k639i+OR+Sr8=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=HXLwSMkGUQJpjeB6H3k1gKeb4bQKtfUE3zfkdtxMdHq9prST9T7R7/v1Ujd8ovI0V eCf2nffXt+2XbJScr13PvgAj/Z2DYBBz/fqVuCsPZIjFQqJo2M2oybxC/oiOMfJ9jH /fmFZXd1qlne4zCEQrqK7ruv7BDqvXt5lHRzqkuPYGd3d2W365qPBWLBsrYKSNX4j1 DX7yT6W15irI9igbkNqy7AvA6APc3nXFkPzv/KpDjvcWf/lU9mfb3ci4l+X0ixBEW0 rrgrUZBXxrzHNG3AYJ5gH2nB/SsjBvhWBNGArrvQkDuFiq8QmaBgF69VSf0+6h4ip6 Pacmx3r5tv4xA== Date: Mon, 14 Sep 2026 16:21:45 +0100 From: "Lorenzo Stoakes (ARM)" To: Kiryl Shutsemau Cc: Andrew Morton , Suren Baghdasaryan , "Liam R. Howlett" , Vlastimil Babka , Shakeel Butt , David Hildenbrand , 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 28426C0011 X-Stat-Signature: n3b1wudqkw4dak9ofg47r3j66uey1n86 X-HE-Tag: 1789399316-871075 X-HE-Meta: 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 67i1s3+k GmYezXST9oHPvr9dL5y5VGt+GPc9UXamFVPjfw1RWEyMMnT7YXR59WmKqH869XLBzHbz+k2rXlse6H9czbZXaAIsUU+nLgsIjdvOlWo/nzGrXnr/bvRh2jiv/A2VwzxQPh8Y3vVU60POEGNGzoKGsrSXZ/zwNS5ZlcWkSJtrRmvUfX+ubQlaN0RInq+AerOIoN88r5mj8FORfCuS9kjojl53DJJ5JVy20DN//ivMX01Dr6ivTLjLpxmSp/GTc7A+M95w0iqmGiIetzxtXZdRNNZ47z/RQ9iMlXC8jMmTOzx3ZepryfXjkk26iFuBVvXsiHixVTek+5vK49X7yaKQwTdRys6CvROSLLqBd Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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? > > From quick grep, it seems you missed two cases of direct readers: > > hugepage_vma_revalidate(): > > if (expect_anon && (!(*vmap)->anon_vma || !vma_is_anonymous(*vmap))) > > vma_needs_copy(): > > if (src_vma->anon_vma) > > Worth fixing? If it is intentional, add a comment why. I don't see it. Ack will check. > > Anyways: > > Reviewed-by: Kiryl Shutsemau (Meta) Thanks! > > -- > Kiryl Shutsemau / Kirill A. Shutemov -- Cheers, Lorenzo