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 E2DD9C43458 for ; Mon, 29 Jun 2026 06:50:00 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7582C6B0092; Mon, 29 Jun 2026 02:49:59 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 72F306B0093; Mon, 29 Jun 2026 02:49:59 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 647AB6B0095; Mon, 29 Jun 2026 02:49:59 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 338376B0092 for ; Mon, 29 Jun 2026 02:49:59 -0400 (EDT) Received: from smtpin25.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id A2A5FA05DC for ; Mon, 29 Jun 2026 06:49:58 +0000 (UTC) X-FDA: 84932025276.25.FE030A4 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf07.hostedemail.com (Postfix) with ESMTP id CCFBD40007 for ; Mon, 29 Jun 2026 06:49:56 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=kBYaXA3n; spf=pass (imf07.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; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1782715796; b=gNQTwIg65eJgfKdEzXTHupl+BIyVrqfrtnrBYZtm3CW8vQ1tdO963i+jdMWd/W3IX71yCp OIQzWOueVyHJf6z1Ab91mGa5XU7hBtQ3pffMs/LDv7T+LWykR13SqeYnZGqPs5FM7gN101 2iXLn88meUqAoFSKSplGgFFb11Sgfuw= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782715796; 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=3rqo+iGnNiPi7WUkA3ir659tVYxJHbxTA/cjOOBMrVA=; b=S051WV1s54AcFp3gKA2f85xSrBfKf7HaWf4/4fZw+wlYUh9G9JwtA1/CmXbBX7X6HQOtH3 gcWa4bkPaPtjqMQ72TID2w+CpI0+sHe/UMtn8qCjMjFQLP3fFoHkfcA2pD2S7+x3rC5hRF VVQt/BzP1tqRkQo1I8Nh/rDeS0P2w10= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=kBYaXA3n; spf=pass (imf07.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 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id C2A004122F; Mon, 29 Jun 2026 06:49:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2D5A1F000E9; Mon, 29 Jun 2026 06:49:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782715795; bh=3rqo+iGnNiPi7WUkA3ir659tVYxJHbxTA/cjOOBMrVA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=kBYaXA3neQO8Uwt2EmclV43XV0y6FxNDWsMHtcixzh4xUbZjwzxaEVsSL74hOvfK8 dAX0Ukj69TNlsNYunSnVKurCP3ZKtJn6IEVG8w0mXE1+7vDN30gwBoQGuHJ4yT+6Xy YgusRPmqGicsY0s3XbM53jANeUhGkeK+mxHHMS/WuZo/8X3QAJQQ5GKtuScy0CW8nl UMfoCtc/C1ev6M1xvg8fvsZM6prtfnsgtmiXTchfMahiOzYIB+EuJ7+gyA+sA4Psaq VR2wRiPleHLAJiTWvcwXf6AKdPPpBrRNM/LIPQcEJi+LROBqFdvmPjOpyFAIKMonPf WmVDV060OILng== Message-ID: <0b5f8b4b-d7dc-4b79-9555-a5b36265f3a9@kernel.org> Date: Mon, 29 Jun 2026 08:49:37 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] mm: memory-failure: fix HWPoison flag race with non-atomic page flag ops To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: Miaohe Lin , Naoya Horiguchi , Andrew Morton , Oscar Salvador , Andi Kleen , Hidehiro Kawai , Rik van Riel , Vlastimil Babka , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Hao Li , Kiryl Shutsemau , Byungchul Park , linux-mm@kvack.org, linux-cxl@vger.kernel.org References: 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 X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: CCFBD40007 X-Stat-Signature: ex4y4q8oh7x47napupok4rfs59wmcwqn X-HE-Tag: 1782715796-409637 X-HE-Meta: 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 mRbVDYgl 81/NOftvxKCUi2KvkMn6EcGDAqNwubcvrkLQU0Qb0YIR2jOzIyuqLym4ousrn8LvzE9v+AKrDnwyWtjkHfOBpYqHbjdVkr5RWwsK63nTEEKgUiRuPWkAOEI7m6uyVlTAlvgakuGSoLxhkWa6AzVP2nLUfch4E8nCA/dx0ACLtfc5zOk/sUNlSsTmTr83P3mjs1b8DDXr755wWPdhTjfT53T9Bslyepx6bzLIb0JXlve+e2iIeq6FlF5UHpNJKOlQt7WHD/YDHkFVmU2BYI2YB+J6hceuQckc1h+Lyfhn8dLMJJzboiATXC+N5gpCh2IVALyaOi5vmtDW5vIInPrDfFC0sg8m1tfOotvZ/MOGMEKx4Zxc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/28/26 23:45, Michael S. Tsirkin wrote: > I don't like it that we are adding overhead to the good path for > the benefit of memory failure, which never triggers on many systems, > but I don't have a better idea. Pls take a look. As I said on Friday. "It's also doesn't address the mf_mutex implications and the x86 thingies I mentioned. ... I'll either take care of that myself or find someone that can work on this with attention to all details. " This is nothing to vibe-code. This needs a real expert. > > Non-atomic page flag operations (page->flags.f &= ~mask, __set_bit, > __clear_bit) can race with atomic TestSetPageHWPoison() in > memory_failure(). The non-atomic RMW reads flags, memory_failure() > atomically sets HWPoison, then the RMW writes back the old value > without HWPoison, clobbering the bit. > > The race was confirmed by injecting a cpu_relax() delay between the > load and store of the non-atomic RMW in __free_pages_prepare, then > running concurrent MADV_HWPOISON injection. The clobbered HWPoison > bit was observed repeatedly. > > This series fixes the race by: > > 1. Having memory_failure() call synchronize_rcu() + retry after > setting HWPoison, so that any in-flight non-atomic RMW that > read the old flags value completes before we proceed. > > 2. Wrapping all non-atomic page flag operations in > rcu_read_lock/rcu_read_unlock (CONFIG_MEMORY_FAILURE only), > so that synchronize_rcu() actually drains them. > > Performance impact (page alloc+free microbenchmark, 200K iterations, > 20 runs, KVM guest, error bars are 3-sigma): > > !PREEMPT_RCU (x86): > insns/iter cycles/iter > base: 12237 +/- 1 17954 +/- 136 > patched: +22 +/- 1 -124 +/- 122 > (+0.18%) (within noise) > > PREEMPT_RCU: > insns/iter cycles/iter > base: 12512 +/- 3 18541 +/- 214 > patched: +95 +/- 3 -12 +/- 161 > (+0.76%) (within noise) > > When !CONFIG_MEMORY_FAILURE, all wrappers compile away completely. > > Suggested-by: David Hildenbrand No ;) -- Cheers, David