From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 5692C606A333 for ; Tue, 3 Nov 2026 08:11:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=e0PDWy3U Received: by kanga.kvack.org (Postfix) id 5C6846B05B1; Tue, 3 Nov 2026 03:11:23 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 59E926B05E6; Tue, 3 Nov 2026 03:11:23 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4A4C76B05E7; Tue, 3 Nov 2026 03:11:23 -0500 (EST) 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 224BC6B05B1 for ; Tue, 3 Nov 2026 03:11:23 -0500 (EST) Received: from smtpin20.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id A44E314030A for ; Tue, 3 Nov 2026 08:11:22 +0000 (UTC) X-FDA: 85393088004.20.694F925 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf28.hostedemail.com (Postfix) with ESMTP id DD0D9C0003 for ; Tue, 3 Nov 2026 08:11:20 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=e0PDWy3U; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf28.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793693481; 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=NQHiBdI0xyIEIllcHZs0yInsfxeb9r5VLhNWBGTa1x0=; b=CaM3guEoZt9MdZXKePB93QSwv+RpgCnC+OCD4cG7vsu4h9lJYpLwr71A9q/TgGpzdnrMnR ZwPcY3YevIqgvVcTS/4fRbhxk2W8dBojVKNQlzPSnfh4KMlN7fSokLqxLWErrGS60eUjrL 2kXYr3dRtbzH8rUSBbWCPhCNq433Yas= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=e0PDWy3U; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf28.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793693481; b=R5Miuodx0zoIB/qXiEkq/+8QA0KYuCbVcVv2uXfGypmG17guEh9Yx7Raa03CEes9KImj/G Z3Hf4N/xCHncngomObkwGv+T2bRT2hw1mGyuaJW3Wq024b6L9kJjVLQHGtLuE0XPqqnCoD BVpcn5OgDPOpKs7YgLa/EPLPCIVtkVs= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 34FCA417D0; Tue, 3 Nov 2026 08:11:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C6B821F00919; Tue, 3 Nov 2026 08:11:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793693480; bh=NQHiBdI0xyIEIllcHZs0yInsfxeb9r5VLhNWBGTa1x0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=e0PDWy3UxP/kvsGnXi328Pmi5xYrEFKmIm6BqK3JTDHYPF2tY3FoTK3QubpCeYr3F l4oWg2OGY045IW9TtLzS46o8lWfHIL4QT7Ane9Ss5goUWsEPx82gTQyuFwMNgSJtVs 6M8Q4c//MKDtw/y3RK9ZpNNBZ9mHPdj0aBt+E9xk6hxDG9yYuJOVYr8Gpopn0voKmL kAjxFci0tl/J/xHJEx9tO8vvhezHhrzK8+rzrCH8OmKa4+YLT0VtYOVGPW1tpl0SfK fdFAJFE3teyviBmhf4zgRc6RoqfIm1Gq4udjutOQHlSb/yUI6NhTJoX5VCpGB2FLpm 6ql8XWecvmK2g== Message-ID: <15b36696-91a0-4128-96e2-e2931a858f73@kernel.org> Date: Tue, 3 Nov 2026 09:11:12 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/memory: use pmdp_get_lockless() for the pmd read in do_fault_around() To: Hui Zhu , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Hui Zhu References: <20261103014749.96764-1-hui.zhu@linux.dev> 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: <20261103014749.96764-1-hui.zhu@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: DD0D9C0003 X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: ayhua9nhba51n9r48afaumujgaus15pz X-HE-Tag: 1793693480-973008 X-HE-Meta: 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 1tU8701B hHJ+ew9zDF6/Q1jK0/7+bxaQEJt6tB2VULuDqIa1MunokY8a0OkZt3XlSQeUaJljdlwR3ZBKm6+HWR/8J7B6aC5A/Zp7mL3fdYZN1BNMnpJ+r2iRyHWnmkeikkjIIKz2Qnedx8M4RikvgrY11IP04KFp1Le/RmaB2udsLTwbR+eFhLN0MBh+BSzNE8trVNuOo79j9aKDRERDyxRoiCIRh6WQOfrV5BhgYP8JZKUS9Ex7G+QwNuyqVFButcnHTLXjdQVnvTjD97W/HtegU9sa9i7FzDr+AcXA71D0Xsjbe2M1+rvsJcWLR5b7hug== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/3/26 02:47, Hui Zhu wrote: > From: Hui Zhu > > KCSAN reports a data-race in do_read_fault / pmd_install; the same code > is in mainline: > > write (marked) to 0xffff8d52a75fb810 of 8 bytes by task 27487 on cpu 5: > native_set_pmd arch/x86/include/asm/pgtable_64.h:83 [inline] > pmd_populate arch/x86/include/asm/pgalloc.h:84 [inline] > pmd_install+0xe0/0x120 mm/memory.c:444 > finish_fault+0x5bc/0xb00 mm/memory.c:5204 > do_cow_fault mm/memory.c:5432 [inline] > do_fault+0x5d0/0x6e0 mm/memory.c:5526 > handle_mm_fault+0x211/0x4c0 mm/memory.c:6218 > __mm_populate+0x144/0x270 mm/gup.c:2207 > __do_sys_mlockall+0x2cd/0x380 mm/mlock.c:764 > > read to 0xffff8d52a75fb810 of 8 bytes by task 27527 on cpu 9: > do_fault_around mm/memory.c:5341 [inline] > do_read_fault+0x162/0x670 mm/memory.c:5381 > do_fault+0x31a/0x6e0 mm/memory.c:5524 > handle_mm_fault+0x211/0x4c0 mm/memory.c:6218 > faultin_page_range+0x227/0x530 mm/gup.c:2156 > __x64_sys_madvise+0x67/0x80 mm/madvise.c:1479 > > value changed: 0x0000000000000000 -> 0x000000001386c067 > > Both paths only hold mmap_lock for read, so do_fault_around() tests > vmf->pmd while pmd_install() populates it under the pmd lock. The race is > benign: a stale pmd_none() only wastes the prealloc_pte, which do_fault() > frees again, and a pmd seen as populated only makes ->map_pages() find no > PTE and do_read_fault() fall back to __do_fault(). > > The load still has to be lockless-safe. pmdp_get() is a plain READ_ONCE() > and can tear where pmd_t is wider than a word, as on i386-PAE where > pmd_install() publishes two words with a single cmpxchg8b. Use > pmdp_get_lockless(), the accessor for pmd reads without the pmd lock and > what __pte_offset_map() already uses on this very pmd a few instructions > later. It is pmdp_get() everywhere else, so the report is silenced the > same way. > > No functional change on architectures that can load a pmd in one go. > > Signed-off-by: Hui Zhu > --- > Changelog: > v3: > Shorten the comment to one line (David Hildenbrand). > v2: > Use pmdp_get_lockless() instead of pmdp_get() (David Hildenbrand). > > mm/memory.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 0fb676dd2bd63..f25c2ce0ef153 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -6017,7 +6017,8 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf) > to_pte = min3(from_pte + nr_pages, (pgoff_t)PTRS_PER_PTE, > pte_off + vma_pages(vmf->vma) - vma_off) - 1; > > - if (pmd_none(*vmf->pmd)) { > + /* pmd_install() rechecks pmd_none() under the pmd lock. */ > + if (pmd_none(pmdp_get_lockless(vmf->pmd))) { > vmf->prealloc_pte = pte_alloc_one(vmf->vma->vm_mm); > if (!vmf->prealloc_pte) > return VM_FAULT_OOM; I'll wait for for review and then pick it up. -- Cheers, David