From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793301900; b=23NSKY1hW041QtTPANlETwY+U3C7FbB3zB4XExaMOlaWSg8dB1GGcPhqGdo2w+N53Lxr /9FaCA5TK0d344HaGKC/vpByOLPPywbpcSrrXBxeRL1fjaycfVv630xMH3hie6fWwUUJf +Iay4oK8pUEX5ATf/9OZC+AiMDSNJZBy2Ijch36UHMe0wnDpi+qYrt/xqPB26OdmHPCMM 95qVacRSSFw61npwL1rFXtkNMwEI34VrP8A8aAUOOaJIls15IFhZpThROwLOq7SRYeMyd Qp4IINCGZxeHHuTdEI1r/4uLBdWbeNhJIi2dNCySG4o1DoWL7HglM7ieunvSUKfY5ZQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793301900; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=vHvd/q4O+h986N5mN9exXE8IloUVYJcmVGFfgDmC9Y8=; b=Kg+BD/p0XP9B1w0HsSqm9SMy4VdNXllk58g/ve/uvfCDbcCwUvRkwr5NSm6q9lcPtjos iX4WY2cbFc+0is9IDCLd6O2UKhT8Wh2yLRcAJ92iOjtl6T+N3fDKn4QGffTbhBj2/R6T5 2UCEYFaH5k49HffxIqv9IgV483ZdJ4AdIyFkizZyIG4DTsesESBiFjmWbeGclp57gsbZG 3PR5qWJOZn4/nDv826IIG8QCF0swSbZRVbreL9hUGUJ5+7+Gxc9ul+35SbK3oBQT58vDk DzvXiGgc60hfo1gHDrtJ/Kz4+OOBlZezoXGqKShlZ1GQuYFDTfRg6IlExVxDt09LwWA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=h2m8gHYK; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id ABB61606A31A for ; Thu, 29 Oct 2026 19:24:59 +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=h2m8gHYK Received: by smtp.kernel.org (Postfix) with ESMTPSA id 819681F01816; Thu, 29 Oct 2026 19:24:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793301899; bh=vHvd/q4O+h986N5mN9exXE8IloUVYJcmVGFfgDmC9Y8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=h2m8gHYKiowIWGROOIGIp2lgHFP799kn2vRajWijcS7Fh+fc7BMZU1zMShcDg9HTG BfUh89iRO16QtmjcQSo0OlzshRrRS6mdNcVNOAxIUViFcgKe21b+qxwWBJcSGsHqoz VEeNeJRVMbHLUGisCtyZPe/4fbCJjZUzlBePLM6WgJguoHTt5sCY168SJ5lmJCrPKc 05VZ7DuHlGYolvsBCbpYBiUfTe5Gup3enN/xMpqUH5GgftDE3ejr+Sv87B6DGXRF9c kSzpiRKxYKfg1rgxL6Bwcb/rrttSBxByJG4kKkAfBWuSaxJhga7fO1vvuLksPwZF5r Vq3miXW1MpUNg== Message-ID: <2c84d8ad-d189-4127-9d1d-8cf0eb40c43c@kernel.org> Date: Thu, 29 Oct 2026 20:24:52 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/huge_memory: use READ_ONCE() when cloning folio flags during split To: Zi Yan , Barry Song , Ye Liu Cc: Andrew Morton , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Lance Yang , Usama Arif , Kiryl Shutsemau , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ye Liu References: <20261029-data_race_huge_mem-v1-1-112e331291c1@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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/29/26 20:19, Zi Yan wrote: > On Thu Oct 29, 2026 at 10:54 AM EDT, David Hildenbrand (Arm) wrote: >> On 10/29/26 15:31, Zi Yan wrote: >>> >>> data_race() would work too. >>> >>> >>> The PG_waiters on the original folio/the original head page is not lost, >> >> Ah, so it's not on arbitrary tail pages, just the old head. >> >>> but there is a chance PG_waiters is lost in the new head, because >>> prep_compound_page() uses __SetPageHead() and can ignore the atomic set >>> of PG_waiters. >> >> Fun. >> ...> >>> Solutions can be: >>> >>> 1. Use atomic SetPageHead() in prep_compound_page(). >> >> That sounds like the right thing to do? > > Yes, simpler, but the atomic op can be costly at compound page init > time. My plan is to add prep_compound_page_atomic() for > __split_folio_to_order() and the atomic version SetPageHead(). Makes perfect sense. -- Cheers, David