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 C66554963BB for ; Thu, 10 Sep 2026 14:02:56 +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=1789048978; cv=none; b=UluNixL0PdFbIYxpMOPvrSHeP3LLBf0cJuBRSWvm8PFUWFpFb0nisMIKrdoSjaG/5gJc8y8xB6v84xWDYMLQ7mF6KToeed7vBlOxevkg1G0h1uGZjvzPnuymtCDHBcWd2dOC5v5ZPhZ64A52ndEiapElu6kzx6bG+WhPW4XmMKw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789048978; c=relaxed/simple; bh=8aIsvPXTu/pIz4UpkptzLCCX3S+Aa/MK8wSV/nc+Mhc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=KK681PjKMIwq5/td6NQG7g8J1vNbaZmm57ffTAJttpVBDwe56Bb4FAJaBgMPtKX9ht0Q4S26TXabGuYV5lDoIAenPJ99Gt9vQX8ZRm60os7iVt4K7cyF09b94cFgOP2mPpfy5tIsFtm8rEDAgLuhdAekTFUQ2Y3kluQTj5soyZ8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fA2x/ub3; 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="fA2x/ub3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A0BB01F00899; Thu, 10 Sep 2026 14:02:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789048976; bh=Qj7jerQrIGn+60nnavoJTceZpIvkRfaJD46i+mDcQ4k=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=fA2x/ub3LYfGaIOregLfIXJPVcmYC7hAkDtUCKcAdCRS0QPrURkadHTHdMm/1fTyn zTBFoqftDYUE6bdM2VNXsSADqAQ7ymuRz8BBrqlC3Vbzc7xzFy9r09pCdObupSaLMz P7e5VmCwBULqN5PprSOoP/xt27w159ha0e67YOhFK7sNSwgvnVDeH9pdOC/gU1sk0P 29L/IjWnH04bauvPl590zCvm4iQBV3l8hFdeulzAw3yIQye2cQpXDzwsgKAez9oe1Y C8kt+nmb3SdVtrrVGVPiiz1EVgRjh4LHtaUctDFh+7GGooCY6MBRlSN4wTALPo7CYD wIKyEW5mIV52g== Message-ID: <7d779a3e-0c12-42fc-91e1-fe53ae2dc641@kernel.org> Date: Thu, 10 Sep 2026 16:02:43 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: implement and use vma_anon_tracked(), silence KCSAN To: "Lorenzo Stoakes (ARM)" , 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 , Kiryl Shutsemau , 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 Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Guilherme Giacomo Simoes References: <20260910-vma-is-faulted-v2-1-e81ebc7d146b@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260910-vma-is-faulted-v2-1-e81ebc7d146b@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/10/26 15:18, 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 > Still using the faulted/unfaulted terminology above is subotimal but I don't mind too much as long as the code is easy to grasp :) > 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. > > 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. > > v1: > https://lore.kernel.org/r/20260909-vma-is-faulted-v1-1-3a701f48984a@kernel.org > --- > index dd66c6ad5af1..40669bec953c 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -264,7 +264,7 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, > * Allow page fault since anon_vma may be not initialized until > * the first page fault. Do we directly want to fix up such comments to not talk about "anon_vma" but instead of the abstraction? Not immediately sure how to rephrase, but I guess the goal would be to avoid the term "anon_vma" and least outside of core-rmap/anon_vma code. [...] > /* KSM folios don't reach here because of the !anon_vma check */ > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 01e7b6b046b6..9f9cd6657360 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -2705,7 +2705,7 @@ static int unuse_mm(struct mm_struct *mm, unsigned int type) > if (check_stable_address_space(mm)) > goto unlock; > for_each_vma(vmi, vma) { > - if (vma->anon_vma && !is_vm_hugetlb_page(vma)) { > + if (vma_anon_tracked(vma) && !is_vm_hugetlb_page(vma)) { > ret = unuse_vma(vma, type); > if (ret) > break; [...] > +/** > + * vma_anon_tracked() - is @vma tracked by an anon_vma? > + * @vma: The VMA to be checked. > + * > + * A VMA or mmap lock must be held. I would document here what the implication is: if untracked, there cannot be any anon folios, if tracked, there might. Some callers of this function (e.g., ksm, swapfile) want to know exactly that: could there be any anon folio in there such that they have to provess the VMA. -- Cheers, David