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 0EF4EE67A9C for ; Tue, 3 Mar 2026 08:48:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3AA456B0095; Tue, 3 Mar 2026 03:48:30 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 381916B0096; Tue, 3 Mar 2026 03:48:30 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 259246B0098; Tue, 3 Mar 2026 03:48:30 -0500 (EST) 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 11F6D6B0095 for ; Tue, 3 Mar 2026 03:48:30 -0500 (EST) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id B52E31C2DD for ; Tue, 3 Mar 2026 08:48:29 +0000 (UTC) X-FDA: 84504125538.19.D907FE5 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf09.hostedemail.com (Postfix) with ESMTP id D841C14000C for ; Tue, 3 Mar 2026 08:48:27 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=sQFhgWr1; spf=pass (imf09.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 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=1772527708; 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=OEcS0O25UdeCMwiY1wLq2u87+WK9pnAlpOZelh9i9R0=; b=v4Vf8LUpFGY4xj0wXiqV+lVe+SDGpRIUSErYDVgzMCFG+0nBJKd9r38/8lHSI4lYMYtt/O E2vOnFzhxlCNpiRj9qHDTlQZNjcqzGlvylIqhlEPKl016gZMZP0hVmFnXTEfaCHJqLzykU LDe7O9lp3Grko3hXpSSDoolToDr1j3A= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=sQFhgWr1; spf=pass (imf09.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1772527708; a=rsa-sha256; cv=none; b=dPtjGkXJduf/Lf2X2JxoiV/sqOmz7VVnWMDD18xZcKXVWB29FWnWrsCuVx1Fkb/0z/fmiV t17ZTx2y7lSwiV3Bu2a5+Klst6aBENHznOox80QtdGlNVfXFygQkyoasWwI7vknqBaWLRk NQpPrLR/I4FokGO0tovTb1q2LuuTR48= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id BF0E242BB9; Tue, 3 Mar 2026 08:48:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F38F9C116C6; Tue, 3 Mar 2026 08:48:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772527706; bh=epD00FefbJXRoRgkmbGok8xKZSTpyougdaUkz5Nbp/Y=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=sQFhgWr1bBwgDvH5hRq8G47VTi6WQCJ47jZwoimCj2jKA7Enu2hks2eyJoG2hcuu9 +T9aQKru/QcnhjqptMENpxixzOMs7BYgp1Ca4+8tHTygnwlYHehpvkmwb2pQrx7Id0 1rpjAeAG2ZA5qwxzkzlpxPNxwKhlXEux0+4Y056pdU6ojid6y/I7WySaGK1iYBObpw 9rzO6kLeeuQSv3dClKh6EI6i+efYyyiX2Pt3cOhHVAOOI0AfY3Qh1kpiBJloV1+FLF 9g+dbil+xnT1DQ4OIKE3h5qWQSP4bHu8NbGxtESdCq0SCAJUCTIyEMpNnRyR992wNP foYgUBA1GAOYg== Message-ID: <56a23a23-cbed-4ace-acef-3ada41bc182d@kernel.org> Date: Tue, 3 Mar 2026 09:48:19 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/huge_memory: fix a folio_split() race condition with folio_try_get() To: Zi Yan , Andrew Morton Cc: Lorenzo Stoakes , Hugh Dickins , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Matthew Wilcox , Bas van Dijk , Eero Kelly , Andrew Battat , Adam Bratschi-Kaye , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, stable@vger.kernel.org References: <20260302203159.3208341-1-ziy@nvidia.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: <20260302203159.3208341-1-ziy@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: meesbe1esyccfogpfn5m14tk7qrjrsmq X-Rspamd-Server: rspam09 X-Rspam-User: X-Rspamd-Queue-Id: D841C14000C X-HE-Tag: 1772527707-7296 X-HE-Meta: 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 Dv1wXkh0 jMHEcQoI6QUWQBY9rf7rAROxJFOIMjpjilnAKkKrS5ppcLdgRe0VqTBbCQLZWRkbjD6Z8V8FFViqrNj+NaqFsPm3XHxuJ4suNcPUNvDsl5GDrKj5wi1JT6wMzg7s/NWjSIxpxs9uQEutvl5BSzPx0JRY4F74mhy7KnmKQkfO/K8oQRUu6keKiPok/0iecltvIX6sa1hVYNPb+7WCnWt04ftfIO704IA6Iq57Wjl3X9WErVb9RUVkw7xW5zg0JEAMzujTbJ22LHE6AZM8Z0svtDrfd6Ud3Erf8+uV3vIA/XcLDdxSQgokh4rGnBfYKA0ngdl+VutjtP4WGctD3bDU8fd+QPVeFdUtu/uzeZZ3iwgz1n0XONqddJ4ln5/6piwjpoCOkTQm3Uf38qBcxZjyM0m/cgvhiQISHsBclc06hYGdemjafFADrVr1AeB6XLV0Hzxgf0QeJUCtI84o= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/2/26 21:31, Zi Yan wrote: > During a pagecache folio split, the values in the related xarray should not > be changed from the original folio at xarray split time until all > after-split folios are well formed and stored in the xarray. Current use > of xas_try_split() in __split_unmapped_folio() lets some after-split folios > show up at wrong indices in the xarray. When these misplaced after-split > folios are unfrozen, before correct folios are stored via __xa_store(), and > grabbed by folio_try_get(), they are returned to userspace at wrong file > indices, causing data corruption. More detailed explanation is at the > bottom. > > The reproducer is at: https://github.com/dfinity/thp-madv-remove-test > It > 1. creates a memfd, > 2. forks, > 3. in the child process, maps the file with large folios (via shmem code > path) and reads the mapped file continuously with 16 threads, > 4. in the parent process, uses madvise(MADV_REMOVE) to punch poles in the > large folio. > > Data corruption can be observed without the fix. Basically, data from a > wrong page->index is returned. > > Fix it by using the original folio in xas_try_split() calls, so that > folio_try_get() can get the right after-split folios after the original > folio is unfrozen. > > Uniform split, split_huge_page*(), is not affected, since it uses > xas_split_alloc() and xas_split() only once and stores the original folio > in the xarray. Change xas_split() used in uniform split branch to use > the original folio to avoid confusion. > > Fixes below points to the commit introduces the code, but folio_split() is > used in a later commit 7460b470a131f ("mm/truncate: use folio_split() in > truncate operation"). > > More details: > > For example, a folio f is split non-uniformly into f, f2, f3, f4 like > below: > +----------------+---------+----+----+ > | f | f2 | f3 | f4 | > +----------------+---------+----+----+ > but the xarray would look like below after __split_unmapped_folio() is > done: > +----------------+---------+----+----+ > | f | f2 | f3 | f3 | > +----------------+---------+----+----+ > > After __split_unmapped_folio(), the code changes the xarray and unfreezes > after-split folios: > > 1. unfreezes f2, __xa_store(f2) > 2. unfreezes f3, __xa_store(f3) > 3. unfreezes f4, __xa_store(f4), which overwrites the second f3 to f4. > 4. unfreezes f. > > Meanwhile, a parallel filemap_get_entry() can read the second f3 from the > xarray and use folio_try_get() on it at step 2 when f3 is unfrozen. Then, > f3 is wrongly returned to user. > > After the fix, the xarray looks like below after __split_unmapped_folio(): > +----------------+---------+----+----+ > | f | f | f | f | > +----------------+---------+----+----+ > so that the race window no longer exists. > > Fixes: 00527733d0dc8 ("mm/huge_memory: add two new (not yet used) functions for folio_split()") > Signed-off-by: Zi Yan > Reported-by: Bas van Dijk > Closes: https://lore.kernel.org/all/CAKNNEtw5_kZomhkugedKMPOG-sxs5Q5OLumWJdiWXv+C9Yct0w@mail.gmail.com/ > Tested-by: Lance Yang > Cc: > --- > mm/huge_memory.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 56db54fa48181..f0bdac3f270b5 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3647,6 +3647,7 @@ static int __split_unmapped_folio(struct folio *folio, int new_order, > const bool is_anon = folio_test_anon(folio); > int old_order = folio_order(folio); > int start_order = split_type == SPLIT_TYPE_UNIFORM ? new_order : old_order - 1; > + struct folio *old_folio = folio; > int split_order; > > /* > @@ -3668,11 +3669,17 @@ static int __split_unmapped_folio(struct folio *folio, int new_order, > * irq is disabled to allocate enough memory, whereas > * non-uniform split can handle ENOMEM. > */ > - if (split_type == SPLIT_TYPE_UNIFORM) > - xas_split(xas, folio, old_order); > - else { Just wondering whether we should no move the comment over here now, so it just covers both cases. > + if (split_type == SPLIT_TYPE_UNIFORM) { > + xas_split(xas, old_folio, old_order); > + } else { > xas_set_order(xas, folio->index, split_order); > - xas_try_split(xas, folio, old_order); > + /* > + * use the to-be-split folio, so that a parallel > + * folio_try_get() waits on it until xarray is > + * updated with after-split folios and > + * the original one is unfrozen. > + */ > + xas_try_split(xas, old_folio, old_order); > if (xas_error(xas)) > return xas_error(xas); > } Acked-by: David Hildenbrand (Arm) -- Cheers, David