From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2A9F4371067 for ; Wed, 10 Jun 2026 07:35:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781076951; cv=none; b=ljgQ0V5hq6tSqft1peg7ZeQIOIK9SWi80BCH4Q+ZGNr7TNzIvJT3NYbtqXQ1iYa5LsJiqDFe90KTYrEPfsXdIaqXzh5CWqlz+4XFpmTWLTp+Aj/Gv+IgPJBV2VdpoTVsBvuGcJ3lHCaTS+PApqij4B01yv7gNw+WGqJX8NjjzMo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781076951; c=relaxed/simple; bh=RyGue1uoNkTxGhwWeHgIqe/l8UCU/NN1IJGM8emsVyM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: In-Reply-To:Content-Type:Content-Disposition; b=gRQuLUjPrqWTeAwiIzuPtwPVCJffbjjNG+UtKt7B7LoGN4wL43iqOMufm6ERrqikkrIk2mPX8nZbeTMYEUMnKBvUSsQOa88HcVt1T7EY+gA/Sydgylu9IH84Vjwl5v0cVSjbgP/w/JTx4YWUh3DrRKbJBdVYEAZ/dJ9rVr39VzE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=LCfyZmvw; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="LCfyZmvw" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1781076949; 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=UWlNJsELOJGMZ+FI7OsgS8pm8RymJ32pYzeA2rVYtbA=; b=LCfyZmvw5CVYSdQfxElWEUXG9mfRK5l/XavNTvWcHjKeamjtbmttwueUFLXjtelho9pV7q Ozgd9RKWmiApXJWb842XpI/1x59pe8p3YlopDEQBw8cm/3MfaGsh4b/qsFJ6g/ypcRxN15 Sr5wFxSH1ycyJRmP9NGeiq+WPuWBoEI= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-517-FeoBXITYOy27XIbFzXxfjw-1; Wed, 10 Jun 2026 03:35:46 -0400 X-MC-Unique: FeoBXITYOy27XIbFzXxfjw-1 X-Mimecast-MFC-AGG-ID: FeoBXITYOy27XIbFzXxfjw_1781076945 Received: by mail-wm1-f70.google.com with SMTP id 5b1f17b1804b1-490afe64f26so31850055e9.0 for ; Wed, 10 Jun 2026 00:35:46 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1781076945; x=1781681745; 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=UWlNJsELOJGMZ+FI7OsgS8pm8RymJ32pYzeA2rVYtbA=; b=iCZ3qbWVtcY5EwVDT73ReuqsZfg+vZh4h0qcPcl917E2b8MvgcrL2xp3FSySxGrykI Mbz5BD4k1cuSZ89GktojTVyXxUD1sRzWKfZgBK3h2Kfg68ZJPN5BsOV+BGwyjchAZLmR zbN7aSq0+Zb4Oks0umwuhPHUgtZHlfpS4Bl0ZwJUTzOK+ljPzNEDcWZ28bHPxsTEv2d/ HVPHn+tsTmj51WITZuqAy2ZmJazgdFoNVSPRGmXPYju25QJJf+K6BErANrXJPt8ilfF0 whAXCoIUluy5vA597Sbb8EFVnvsuGVx8pCYvkrhlO8fV6ry8kNzLFvT92V4mBJtiuVgV SDUw== X-Forwarded-Encrypted: i=1; AFNElJ/q05KjfPFgU7hxtuFhUhwJ2e4xr5VDNKCmhSfCuFBcpVK/X/6yoL5fwAEv5aOoqVxY2xloaWEDFl+BZWZGvQ==@lists.linux.dev X-Gm-Message-State: AOJu0YwOVNu9o1JEEd2UL/TsYxQK8O5ZilfROP9avKtzpRO6Srx16yk1 i/emtsiL8w3if55jBDFULXe79BOJqtcTIEDEMx5sYT2IgSMDPr7ASNSH9igTxV94V83MEdvxSEp 2h1Pzhb8lXurViZjiYBq5GC5/jEBgw12tUJuOevMRfsiJit4hKUryTLz8XwFEjMMKWASp X-Gm-Gg: Acq92OHdUvnAYs+4y4/d0fWpH8pM39eiEIkXfAoOVBsv5OwCugNzJiUFlzc3Jkl/Wjo YEnDmKezZ0xPsYnrD6lE6azfqgKw8TEEhinw0x4GvFDTVvsOFHMVsK4s7V37b13hsaP1Ot5HcND aabV7NMRD1HImL7gpak75MX6rUKWEyg2nc4X94H0Nv8JSAswvfGhHqNvkAQd94+baeO7ljXIMFw eIoBNpAJw1GPL93Pb/bm6yNtUNsxD3oCGvgxsbIxwkyIAURT4qAPonB89Vc6MAkVGvY7itAW1rd YTZUUs6PibNXApidLUw0tsFUGDUEppcP8QjecMF30IHVtvp4HzEPpuxpKI21NaIHS0VZmpW3D93 uAvNVl72oZDNE7tksp9uiSOI+3tefJYswJPHA9gu/NtXl9s89P+zKZw== X-Received: by 2002:a05:600c:3588:b0:490:4b89:5372 with SMTP id 5b1f17b1804b1-490c2cf5433mr343576425e9.11.1781076944750; Wed, 10 Jun 2026 00:35:44 -0700 (PDT) X-Received: by 2002:a05:600c:3588:b0:490:4b89:5372 with SMTP id 5b1f17b1804b1-490c2cf5433mr343575795e9.11.1781076944181; Wed, 10 Jun 2026 00:35:44 -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 5b1f17b1804b1-490bc391aaasm627725935e9.1.2026.06.10.00.35.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Jun 2026 00:35:43 -0700 (PDT) Date: Wed, 10 Jun 2026 03:35:37 -0400 From: "Michael S. Tsirkin" To: Miaohe Lin Cc: Zi Yan , "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: <20260610033441-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> <20260609165829-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: bGlml3-3rBCpQQMS-kT0R6vDYx3c28ae51Phda_RJxI_1781076945 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Wed, Jun 10, 2026 at 03:24:30PM +0800, Miaohe Lin wrote: > On 2026/6/10 5:00, Michael S. Tsirkin wrote: > > 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. > > Since __free_pages_prepare() executes entirely locklessly, the only way to ensure > HWPoison flag won't be lost might be only set hwpoison flag iff we can make sure > pages are not on the way to buddy... > > Thanks. > . Right so here after take_page_off_buddy it's ok, for example. -- MST