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 35983CD8CA8 for ; Tue, 9 Jun 2026 21:01:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 53AE66B00E1; Tue, 9 Jun 2026 17:01:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 511C26B00E2; Tue, 9 Jun 2026 17:01:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 400026B00E4; Tue, 9 Jun 2026 17:01:13 -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 2C5E26B00E1 for ; Tue, 9 Jun 2026 17:01:13 -0400 (EDT) Received: from smtpin14.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id B18CA407B0 for ; Tue, 9 Jun 2026 21:01:12 +0000 (UTC) X-FDA: 84861594384.14.B9B532F Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf23.hostedemail.com (Postfix) with ESMTP id 54F2A140008 for ; Tue, 9 Jun 2026 21:01:10 +0000 (UTC) Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Pc6iAmv1; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf23.hostedemail.com: domain of mst@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=mst@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1781038870; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=0Om/173xa6nAXXlawHrWQ0qeVuAob6cSlyHSyIFpCw4=; b=2powd8kn3z9J2ZjLjC7VnT+fMF6PUi4y74bMOFyWGhutsbhilXygN/X1bjJChD8b/pYHfg SGoDFTp/8k8Ne/3rQ8tSa5GEAUF/3te7nBs4nrOHDX6R6kaCyq6WaetZw9gjy5NgEhehzm jJOLykEH0oNETeDonD7/5SltxmYOPIk= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Pc6iAmv1; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf23.hostedemail.com: domain of mst@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=mst@redhat.com ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1781038870; b=8q/27wVJppY9NSd0B1udNl7qLkHXTBz2oXoMasODXaMWXMdfaQyTFxGchjYCIY/PjPL0N3 138BkVXpzsspUbHWof25BpcvA+PAwokke5iaXUiS2P8wynWKSpBC8q3TI8LnAEyrDblKqF EuLhNTAl8VXDDpONavlDGKkfcT7ee+Q= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1781038869; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=0Om/173xa6nAXXlawHrWQ0qeVuAob6cSlyHSyIFpCw4=; b=Pc6iAmv1fLWH74AGTT9KqnYaFqx8lrYNNSFU9h2W7I9+aNDRQE6i/+5660EFOJGBbGlpMY RrryO7j1Bq7uB9+Q9bIbWeLu+rnepjhkk0gX+668C8nXdS62U7QlTM7XG8fdcyYZ7qBDxV OhES06+5FSTdiwsQoIyjflum9pGvLiw= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-376-_jIPBi9DPkqfFHU6oAuGoA-1; Tue, 09 Jun 2026 17:01:06 -0400 X-MC-Unique: _jIPBi9DPkqfFHU6oAuGoA-1 X-Mimecast-MFC-AGG-ID: _jIPBi9DPkqfFHU6oAuGoA_1781038865 Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-490b3ec3f7fso38791215e9.1 for ; Tue, 09 Jun 2026 14:01:06 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1781038865; x=1781643665; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=0Om/173xa6nAXXlawHrWQ0qeVuAob6cSlyHSyIFpCw4=; b=ZsZdE54n0zivIFFBeNSiHPsbXWIJjVL9EwcsTqlLeRwxa3Fafr73t7nb/kIbJtCIns RR3uVtvY1XsQFqSuW2rRBu5yH/LK+tLASoIQ2WtZ22psqj++sA982TjSaAgb1BarbTjT frm7MJwD68RNB4vOgn+6QlFYlFvNmJaxSHIm5SSrDy1lql4ff9VmKgBlkGgn3YGni1xQ JSvzeWnIdjCJR7wmG0rSYXnCpZaFMW621LLD6BrX3iGJyQ5QTAgsb95BBC2opTdBLYYA 1SKkZje5JWEdMNPpPFeYA9N2r2FWcgQpFvyuSqUX2xRuUFKCxSMvsaTvx9/DDVOkrCqA TDiA== X-Forwarded-Encrypted: i=1; AFNElJ/uW8aPqkN/THkJ+t7nrwVf2ohWkzG3tsKrJ6apylXm6WDeaeB15ak/+KIPO+SfQ4WzA092EqWmeA==@kvack.org X-Gm-Message-State: AOJu0YxcywjfuebumGnUGBIwPRKOt5qdOnBPgNnL5oRTM64ZAz2BNfa/ VFCFGvULCvWjqwLSmNIEzW6ZdaQsjgrbpoMb1Dli6gN+nvJUxOklT0EtzG8epUlXOHGx0x75ZK6 hwCWDkhQ/nA4F0oNa/kkzk124A7i6ZvHNZlOIUhsjpIEIzHL90Pk2 X-Gm-Gg: Acq92OHwIKqORImc1cZrmDHysMPB7n5Hf903/LQb4tMmlea3jubtzbGVsfpwtozR9i7 uPNK0FdhPRqQzO9X/FFSJiQokcnUaX7xf+jM7aGvdQCd/F65TGOA/7lrMRjgYn7niR/W7Mk8X62 BA63DooEJqt2k8KWuw2AzNYbGayUDTeBJeJEcb6jGU/AVlPoi4Ry3WFGp3bcxwZvmdOkKwfbDwV Sjb++kj7bxdhi/6A3o5QozJk7VAgkJ+84BfREJqvWC+mjV6+Cs+4qZTQue7spjIbuZixvdbU4sI dTnLxSipJzOyCExB8fGOxIIwNkB1bFEDAX6LeQpAomHo+VHbxfSv+yWklUPHGImNHououedJlI2 R4cNEfzpIPzFalk6cVhviIwFFO9OEXk18cT0FVTzW8ZEhvhnMdwEHDw== X-Received: by 2002:a05:600c:1907:b0:490:b99c:9337 with SMTP id 5b1f17b1804b1-490c25a0800mr343765475e9.10.1781038865124; Tue, 09 Jun 2026 14:01:05 -0700 (PDT) X-Received: by 2002:a05:600c:1907:b0:490:b99c:9337 with SMTP id 5b1f17b1804b1-490c25a0800mr343765005e9.10.1781038864641; Tue, 09 Jun 2026 14:01:04 -0700 (PDT) Received: from redhat.com (IGLD-80-230-85-71.inter.net.il. [80.230.85.71]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4601f2dc577sm66817831f8f.3.2026.06.09.14.00.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Jun 2026 14:01:01 -0700 (PDT) Date: Tue, 9 Jun 2026 17:00:55 -0400 From: "Michael S. Tsirkin" To: Zi Yan Cc: Miaohe Lin , "David Hildenbrand (Arm)" , Andrew Morton , linux-kernel@vger.kernel.org, Jason Wang , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , Muchun Song , Oscar Salvador , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Hugh Dickins , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Axel Rasmussen , Yuanchu Xie , Wei Xu , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , virtualization@lists.linux.dev, linux-mm@kvack.org, Andrea Arcangeli , Naoya Horiguchi Subject: Re: [PATCH splitout] mm: memory-failure: serialize TestSetPageHWPoison with zone->lock Message-ID: <20260609165829-mutt-send-email-mst@kernel.org> References: <20260609111020.e88f51a7b6ebc37360d66fdc@linux-foundation.org> <8c1f468e-b50a-487a-a267-8d1ea5a61c87@kernel.org> <38C84F23-E881-4DB2-86BA-93F39D44AE1B@nvidia.com> <20260609162437-mutt-send-email-mst@kernel.org> <4BA276D9-9EB9-4E2A-8A05-657ACACFF227@nvidia.com> MIME-Version: 1.0 In-Reply-To: <4BA276D9-9EB9-4E2A-8A05-657ACACFF227@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: RJlGs7FzbEABU4Far5rRpjFZ4XmCp1beRWeseH7Y3Ik_1781038865 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Queue-Id: 54F2A140008 X-Rspam-User: X-Stat-Signature: zoat1q8369au7jzaamed3emm8z9qd5ih X-Rspamd-Server: rspam09 X-HE-Tag: 1781038870-77047 X-HE-Meta: U2FsdGVkX18ge9X2DNKlbuejLWu/kRVTQfec8AT5nDTrNZzI0wuwxUdVa95QyRWuhmg1vF6I4QwPXS6EWCuz9+tmBZYp25lL5vB7xO0kchDZrubCR2Kxrz0DLmDX0Eq8WehIeDXOKX9w+K9/uclXbdpYur4KK7WemU5Us3SEEvx6Z5awmsdN1HIR83HwNgcuz8AC/e1yGtiXf4GeZBDZdFZMgGZIYij5u/X45dHjcFmgpHTxzcC9MvzsY+AGPFZz1R8oKMljp2pZc+F5AnT0wNHs2SqMSqwD8L2k10QMH3PmdLrn5gmNrDMliTXck9N+4PRSOTw3zrejDrLlVodZHnvoDUlOUq76W5BBy1gjtxTuvR8ZbeiraQC1UN7ISpoN2ZICd3cpIIebzzkjCdmllYIvvQclOVL+9SLgKJxQlFE5bk7ZF/ZfhfMY/OVdvah+fPhqcgqEwuvJlETdhB+I1TqJYS9T992KA/yq0d+SsaJJEVpK046hroyJiMZ62+q4HD7WeMG0CF00RSCu24fZAtb/I4lSvTTqCvv3OwfdS4gWIndVXXiYTNPAAL2/yU+HvwJZNbLdxmTdps9Yc20kIR1p091s2PxT8pf+P9pAxSQOk2KsNMYl2BDnGP4g13KThQfAyl30l5FngNgIJeoohfLiYpKe6VrVUgfWP3xKS1LPt9MM1HOBU7JsAmxG62EKXRmNPcEr94vzpMoEu8lQSDiv1KuZjK0HKDZmdNFa1MPA8pCtucGf9oOMj/DwHyDTMf2lJWDO2rLlU9eQ2sQ0daN5sbb+NYRKn5M7tM5axbyF685GpePR3Z9FAOSn1qsPa4d3MMPTs6xd4/9179IKGmznMNfizxxfXHb8hrX3TEcU3NbCb8TqLimbhr7Le466ydz4tLc0NA/gaCS/Scy8ATGYncnOpcw5E1p8l75kl/3V2Vayvjhwo2ehFx7yZTrUTgRGZOCES2m+XG9MVIt AVDkQs/n 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jun 09, 2026 at 04:54:01PM -0400, Zi Yan wrote: > On 9 Jun 2026, at 16:34, Michael S. Tsirkin wrote: > > > On Tue, Jun 09, 2026 at 02:52:47PM -0400, Zi Yan wrote: > >> On 9 Jun 2026, at 14:39, Zi Yan wrote: > >> > >>> On 9 Jun 2026, at 14:38, David Hildenbrand (Arm) wrote: > >>> > >>>> On 6/9/26 20:10, Andrew Morton wrote: > >>>>> On Tue, 9 Jun 2026 06:12:49 -0400 "Michael S. Tsirkin" wrote: > >>>>> > >>>>>> TestSetPageHWPoison() is called without zone->lock, so its atomic > >>>>>> update to page->flags can race with non-atomic flag operations > >>>>>> that run under zone->lock in the buddy allocator. > >>>>>> > >>>>>> In particular, __free_pages_prepare() does: > >>>>>> > >>>>>> page->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP; > >>>>>> > >>>>>> This non-atomic read-modify-write, while correctly excluding > >>>>>> __PG_HWPOISON from the mask, can still lose a concurrent > >>>>>> TestSetPageHWPoison if the read happens before the poison bit > >>>>>> is set and the write happens after. Will only get worse if/when > >>>>>> we add more non-atomic flag operations. > >>>>>> > >>>>>> Fix by acquiring zone->lock around TestSetPageHWPoison and > >>>>>> around ClearPageHWPoison in the retry path. This > >>>>>> serializes with all buddy flag manipulation. The cost is > >>>>>> negligible: one lock/unlock in an extremely rare path > >>>>>> (hardware memory errors). > >>>>>> > >>>>>> Note: SetPageHWPoison and TestClearPageHWPoison calls elsewhere > >>>>>> in this file operate on pages already removed from the buddy > >>>>>> allocator or on non-buddy pages (DAX, hugetlb), so they do not > >>>>>> need zone->lock protection. > >>>>> > >>>>> Sashiko is saying this doesn't do anything "Because > >>>>> __free_pages_prepare() executes entirely locklessly". Did it goof? > >>>>> > >>>>> https://sashiko.dev/#/patchset/df06b66fe4ff8e925ee0714955abc2183a727b90.1780998980.git.mst@redhat.com > >>>> > >>>> Battle of the bots: it's right. > >>> > >>> Yep, __free_pages_prepare() changes the page flag without holding > >>> zone->lock. > >> > >> __free_pages_prepare() works on frozen pages and assumes no one else > >> touches the input page. To avoid this race, memory_failure() might > >> want to try_get_page() before TestClearPageHWPoison(), but I am not > >> sure if that works along with memory failure flow. > >> > >> Best Regards, > >> Yan, Zi > > > > > > > > Actually memory failure already plays with this down the road no? > > > > So maybe it's enough to just SetPageHWPoison afterwards again? > > > > > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > > index ee42d4361309..4758fea94a96 100644 > > --- a/mm/memory-failure.c > > +++ b/mm/memory-failure.c > > @@ -2415,6 +2415,7 @@ int memory_failure(unsigned long pfn, int flags) > > if (!res) { > > if (is_free_buddy_page(p)) { > > if (take_page_off_buddy(p)) { > > + SetPageHWPoison(p); > > page_ref_inc(p); > > res = MF_RECOVERED; > > } else { > > > > > > and maybe in a bunch of other places in there? > > You mean for fear of losing HWPoison flag in the earlier TestSetPageHWPoison(), > just set it again here? Yea. > Why not do it after get_hwpoison_page(), since that > is the expected page flag? It's still in the buddy at that point right? I'm worried buddy might poke at flags. > Miaohe probably can give a better answer here. > > > Best Regards, > Yan, Zi