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 B3AE1FA0C43 for ; Wed, 15 Apr 2026 08:04:51 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 117646B0093; Wed, 15 Apr 2026 04:04:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0C7E66B0095; Wed, 15 Apr 2026 04:04:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EF9226B0096; Wed, 15 Apr 2026 04:04:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id DA9706B0093 for ; Wed, 15 Apr 2026 04:04:50 -0400 (EDT) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 863551603BC for ; Wed, 15 Apr 2026 08:04:50 +0000 (UTC) X-FDA: 84660053940.12.21487AF Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf02.hostedemail.com (Postfix) with ESMTP id CF30B80008 for ; Wed, 15 Apr 2026 08:04:48 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Fs8l7fTu; spf=pass (imf02.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@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=1776240288; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=I17gY1VQqAFFn9QfiY1ygRtudFtlgtD9DJehm1faeYM=; b=Rg/kiMO2yiAbGAcZVQKZ1vd1UJNs53kRkkg7lFdiXop8oDSTSXywP1yEhyY4jkdwbNJPxR Xkz8OSkA8U2cvkxsVhVVsFe9nh30kFub65CntVYkpmro8pBCFwO1kssKl/t0tolOTOhlNP jHoqQCk1gXzckQmdkhOC2Zv6gYKqQw4= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1776240288; a=rsa-sha256; cv=none; b=6EBL+25+y07o3YNDRDtZv5/JPVkVpeKtLHpo+/o3JKJWH/dzBXS7t96UPY5v8c+68cKD/x g8nuYh+Z9DYSZx4q0KibzTE8K+aJXi7bOVCf0/WMG17whMs+kVi0MUSADZ43wpCW4Arcsr Cu8piWpZ2jR9RP8ji+sbgSpkOxmU0tM= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Fs8l7fTu; spf=pass (imf02.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 26B2B6012A; Wed, 15 Apr 2026 08:04:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BCFDCC19424; Wed, 15 Apr 2026 08:04:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776240287; bh=871zzdzT4SrXceIZaJieI+YzRKMftM9KovcUV8+EOYs=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Fs8l7fTuVLvJS8nZ4H2fGZVoOH5TUxz+qBME9VCxjOZjAZfrYAOpWcbs+5T+uL/ce LuEywyo6kWxLDDsGUhMTXtvI6Eb9JwkznyUKyHBDNPA+tovJCwW+0ZNuvcAy6uEenL ibdeZCYDI6z/sMbd7lPQDJqy+Oys7CD0az/Zmumr0fvT+N2sPnr5ks3U2JL9zlJDZe 5hKfEByenRcvxG6iltzohnAAQd6IxhJgr9M6Xt0c7TIy4gr7AIChQ8riMJrZOTPGab 770Agpi7/s3AOkSZXN2n61MlixwwHtXj6CZrJiyPSfnZtN2QZeWdTgNrhP8ZmdhPjA gm9ub/wuoLyNw== Message-ID: <09d1ef13-e02b-41e9-b431-4c3254e42011@kernel.org> Date: Wed, 15 Apr 2026 10:04:38 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/sparse: Fix race on mem_section->usage in pfn walkers To: Muchun Song , Andrew Morton , Oscar Salvador , Charan Teja Kalla Cc: Muchun Song , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org References: <20260415022326.53218-1-songmuchun@bytedance.com> 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: <20260415022326.53218-1-songmuchun@bytedance.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Stat-Signature: jgs3j3bh7e8u84t96znb793tboh1mr81 X-Rspamd-Queue-Id: CF30B80008 X-Rspam-User: X-HE-Tag: 1776240288-74521 X-HE-Meta: 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 YUnprrfk TmLWHV17dTWyeNLJo3LTKSZni5Oky+PN9Q29Yw4Im4UdEQkyRcbs4LyWFJAM0oti8JdngcNZuRxePIe9qqK3KcgG4/wXGgkoaAasdPbIomK0Cuh8KebzZXZYErQN8r0BYuKKrBp3+Pu6squVW8spZLnM9jOTd0zhWgV2IXSjMIba5kUWmwUVdRYGXsLy9LeUMVJmapp6fgqaRG+fAx34m82CMfbZAmu9gpiC+FwFDCJUPWp9CP46Ox3s6y4kt7AQWAwsYC1CASDRqtCyxKM9oMVUCjkTydm+5Z2FeGbRzswZDJLaotmB+35kpeUXmt6AmSrEoSTo7+FJrT9E= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/15/26 04:23, Muchun Song wrote: > When memory is hot-removed, section_deactivate() can tear down > mem_section->usage while concurrent pfn walkers still inspect the > subsection map via pfn_section_valid() or pfn_section_first_valid(). I'll note that it's all racy either way: someone checking pfn_valid() / pfn_to_online_page() can race with concurrent unplug. We've known that for years; it's hard to fix; it never ever triggers :) So is this really worth it, when we should in fact, work on protecting the users of pfn_valid() / pfn_to_online_page() with rcu or similar? -- Cheers, David