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 7045FC43327 for ; Mon, 29 Jun 2026 08:21:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3236F6B008A; Mon, 29 Jun 2026 04:21:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2D9F46B0092; Mon, 29 Jun 2026 04:21:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 175E56B0093; Mon, 29 Jun 2026 04:21:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id D97BC6B008A for ; Mon, 29 Jun 2026 04:21:55 -0400 (EDT) Received: from smtpin21.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 5747D40509 for ; Mon, 29 Jun 2026 08:21:55 +0000 (UTC) X-FDA: 84932256990.21.3CA3A53 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf29.hostedemail.com (Postfix) with ESMTP id 95D25120010 for ; Mon, 29 Jun 2026 08:21:53 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=eJM17GOj; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf29.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1782721313; b=sRs0YrsYWRPYTGsVvEHx4Met7G6nLefJc71EuOBRMx72/zyt6Lmc3ED2Z09XFYdrP2w6qk VqX7Kj8PKyS88m15mezBmbGGrPLQrxDWQWikVvdANutUafor2NcxUByxMiKdJgJACiHj+F bMKiP7q099g/lLilIBQPv1lt7hU8/1I= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782721313; 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=PTgXkbvVLbmjixblka4EX/WB3VrVuB2RapiXZ8W+wIg=; b=bHISADb/5MOXPCoEVpSGrtUJ31zQ6YCWqxGWSrUoDu3Ir8MSr4UqPuNOlIhCe4D3/YI6lX RS/G/FiNFG05bAw1H1U2ajSRzLclxsbrKvw5r5hYz0BrZaYkvpJ1XupxiuxeTv3UfplGWB OTEfapRoMtRRJ8hOp+7yDkrETL1/flk= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=eJM17GOj; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf29.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 22F146001D; Mon, 29 Jun 2026 08:21:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D59D11F000E9; Mon, 29 Jun 2026 08:21:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782721312; bh=PTgXkbvVLbmjixblka4EX/WB3VrVuB2RapiXZ8W+wIg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=eJM17GOjQPe7POwFKir2rKmQvXq1KG08ah06Lp5zlKQ3rzcdympN++OKKa2ZVsntv WTQC2r8gNLJclFMRpjNVhWgB3qqGuos9yaea9mmVHx/HvYLL1tYLsPlNNedCSiau3z A6eL0rLU0obT2P+QtewXrxyf3zoEYRktkL43EYOZ2YlAfHg/w9m1JkST9DS69NqUOS XMXRTj7GOruKPSgfEp4epYL12ulnANdMWVLsNJHGTLMep2UW5WAzOG6cS28huhaMUy r37erDxj9w5NjwglaiWEy56P9PIkxcjhLKOBLSrw60geyFBz9vGd0Eel4WigqDN4Wi 4FAENakVFTM0g== Message-ID: <4709b993-85aa-470f-a346-2c3ea36bc4d4@kernel.org> Date: Mon, 29 Jun 2026 10:21:42 +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" , Andi Kleen Cc: linux-kernel@vger.kernel.org, Miaohe Lin , Naoya Horiguchi , Andrew Morton , Oscar Salvador , 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: <20260629033608-mutt-send-email-mst@kernel.org> 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: <20260629033608-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 95D25120010 X-Stat-Signature: wh16pwr314s5fhjr5peuqy714fho19w7 X-HE-Tag: 1782721313-710047 X-HE-Meta: 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 xv0l2Eyy ch3MocLFwlMUjbbTw7XJlrVEWz8cEiFfq1Q1BUOH0GoAGLMW0Gjot06K2kmPxu/Mb8e+bkEg/brXy1OjdwfB7E3Jq2a5zi+MoyGZ3c+jHf9bJAYI/s3q3zv3GYPM3LcdWXDg8ntOw48peLpXu3nMKNnJCw6EfciWJEScP2gUDZCGU5zSpcKZVc1YWOVTlK3j9fa88pESBK3Sk/3hm+6gtwj3SNMikwGS3salqo/efyL4+UeTqu4Ki+m3qxGa8elU9VCk8vFSMvitZ4dzBRrnoMfEchkzUR1OC1jljYRFJHXUHYuTjO4etHBy5nE6q9M42Xbr5qVytJqHerCb7kXa8ZLql0w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/29/26 10:10, Michael S. Tsirkin wrote: > On Sun, Jun 28, 2026 at 07:11:58PM -0700, Andi Kleen wrote: >> On Sun, Jun 28, 2026 at 05:45:22PM -0400, Michael S. Tsirkin wrote: >>> 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. >> >> It wouldn't surprise me if your underlying performance assumptions >> -- an non contended atomic is cheaper than a rcu_read_lock/unlock -- >> are not true in various CPU/kernel configuration combinations. >> >> Modern CPUs have fast atomics when uncontended in normal circumstances. >> But it probably doesn't matter much either way because the difference >> shouldn't be very much. > > > Hmm. It's a bit silly that I didn't try. Seemed clear to me, but, > on this old xeon... > > insns/iter cycles/iter > ------------------------------------------------------- > base 12238 +/- 1.0 17889 +/- 97.9 > rcu_read_lock 12251 +/- 7.3 17991 +/-191.6 > atomic ops 12233 +/- 1.9 17733 +/-136.5 > > > The diff in the noise. > > And old, slow CPUs maybe don't have MF at all. > > So maybe just atomics instead of all this mess. That would be much better. What I was concerned about so far was that many distributions enable hwpoison handling unconditionally (independent of any specific CPU!). I recall running experiments on some not-so-dated hardware 2 years ago (when optimizing out rmap atomics) where additional atomics really hurt, even in uncontended cases. > > > > >> It seems very complicated for something that >> could be much simpler. >> >> But I guess it's fine. >> >> -Andi > > Indeed. David already said he's gonnu look at this himself, but he If we can go that simple route (I'm not sure yet), your patch would be fine. I can try finding someone to run more experiments on arm64 hardware. -- Cheers, David