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 9586FEBFD22 for ; Mon, 13 Apr 2026 09:19:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 05BB26B0089; Mon, 13 Apr 2026 05:19:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 00C3B6B008A; Mon, 13 Apr 2026 05:19:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E3D8D6B0092; Mon, 13 Apr 2026 05:19:52 -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 CF81E6B0089 for ; Mon, 13 Apr 2026 05:19:52 -0400 (EDT) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 80975160CB3 for ; Mon, 13 Apr 2026 09:19:52 +0000 (UTC) X-FDA: 84652985424.15.04DBB93 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf14.hostedemail.com (Postfix) with ESMTP id DE978100010 for ; Mon, 13 Apr 2026 09:19:50 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=bNCjDuM+; spf=pass (imf14.hostedemail.com: domain of rppt@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=rppt@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1776071990; 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=CKxSA0n9kVvCKpIgcv8zNS+kU9VEMRkmxLm1MYSpV4Q=; b=3bscHPT72e4xluS1/YHItjm3hzzv1+xOo0Jemk2VEkqJKfqx+h8MPti8HoNZEb0EWIWyz3 GTjnuhYqOkaXLDb0+rcrjkPI6JI0gtELvBRS6B8o/Xsiej+fItV8DHIGCimmI48ipc2/oQ CR0rir6AKSUTsLreeXMDi5st+EPUNqY= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1776071990; a=rsa-sha256; cv=none; b=EDPtGhvJM8qHDHG3gFH2Nl/OQ+hWnJxTgHoQx1k8C+ERh8RC56phUok4CNuraCSyjtw5fT TS6otyNqsxdb4AFQXBIobYILW90HJFngfmGJRvqIaBO86lCIxKLnTYRc09EPLHYw2zXQBP BGhuFDjfrfz1F+Y9HEQewtyjHH0Cfrs= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=bNCjDuM+; spf=pass (imf14.hostedemail.com: domain of rppt@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=rppt@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 47B2C60180; Mon, 13 Apr 2026 09:19:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8A895C2BCAF; Mon, 13 Apr 2026 09:19:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776071990; bh=2kr+EhMgMQkHVA7iNdaf14YX9cd4ab4OO+SsmIGEbRU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=bNCjDuM+e/DnQ3gdIUmaMsSzHbtpAX1fNz8FDMsrhCBz/Zx234Yd2VLPGUFxItza8 AGkMDnomVyAINuiid0nMJwgViqv6xnF0ti5KODcY4pyAGB0gvsbzVtAdAUc5GmMZbE 4k1neV8aNrD6Lpn60QOG7yrpG4PiWQyK1Ti9YnbZoMEYnDCKAVSCXhsDBQqsR3+UWr pxPdV/KIztvfBFdZiRSYDKR4uD8+uS7NbfzM3NXA+lJTQGp1iZtA8VqoX2Of8xzSq1 Mtx68qhJuw2Bg363XiG/wIQEmy4oZ5Zp99fI74eCFh4iiBcHG3vA+W8vlfZZ4hwfwX yQuDf3Qdn3Rwg== Date: Mon, 13 Apr 2026 12:19:41 +0300 From: Mike Rapoport To: Muchun Song Cc: Andrew Morton , David Hildenbrand , Muchun Song , Oscar Salvador , Michael Ellerman , Madhavan Srinivasan , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Nicholas Piggin , Christophe Leroy , aneesh.kumar@linux.ibm.com, joao.m.martins@oracle.com, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 01/49] mm/sparse: fix vmemmap accounting imbalance on memory hotplug error Message-ID: References: <20260405125240.2558577-1-songmuchun@bytedance.com> <20260405125240.2558577-2-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260405125240.2558577-2-songmuchun@bytedance.com> X-Rspamd-Queue-Id: DE978100010 X-Stat-Signature: yh9dhtt83yipcba48pweg7faokqsgd5e X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1776071990-966633 X-HE-Meta: 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 UNo+63LQ MmYEibTCTHhpZFcbPx3EW9qs837gU6753Ntg/J0pVmTOjjsoX0eWe2kGc2jdhttNz7b8/mhYS+lYa/AMRIJoanSMVaKxrV4PC0APGQhTGlqAqZxK5bxP72hhq3VoPYgCKLYJh8zTh32fXShETKudbik248ZpTNPj1PS0hdeVMSQTHgga5PeDaDLqwQQklch7PixAtc/7OOeCeDw6mxb0CScQq+wZ0sT9BLJOQKDjkzeqMewxcBKchXAbCbG78EH0Cf5jv4nnX6b3G/R01f7oi9T5svg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Apr 05, 2026 at 08:51:52PM +0800, Muchun Song wrote: > In section_activate(), if populate_section_memmap() fails, the error > handling path calls section_deactivate() to roll back the state. This > approach introduces an accounting imbalance. > > Since the commit c3576889d87b ("mm: fix accounting of memmap pages"), > memmap pages are accounted for only after populate_section_memmap() > succeeds. However, section_deactivate() unconditionally decrements the > vmemmap account. Consequently, a failure in populate_section_memmap() > leads to a negative offset (underflow) in the system's vmemmap tracking. > > We can fix this by ensuring that the vmemmap accounting is incremented > immediately before checking for the success of populate_section_memmap(). > If populate_section_memmap() fails, the subsequent call to > section_deactivate() will decrement the accounting, perfectly offsetting > the increment and maintaining balance. > > Fixes: c3576889d87b ("mm: fix accounting of memmap pages") > Signed-off-by: Muchun Song > --- > mm/sparse-vmemmap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c > index 6eadb9d116e4..ee27d0c0efe2 100644 > --- a/mm/sparse-vmemmap.c > +++ b/mm/sparse-vmemmap.c > @@ -822,11 +822,11 @@ static struct page * __meminit section_activate(int nid, unsigned long pfn, > return pfn_to_page(pfn); > > memmap = populate_section_memmap(pfn, nr_pages, nid, altmap, pgmap); > + memmap_pages_add(DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE)); This logically belongs to success path in populate_section_memmap(). If we update the counter there, we won't need to temporarily increase it at all. > if (!memmap) { > section_deactivate(pfn, nr_pages, altmap); > return ERR_PTR(-ENOMEM); > } > - memmap_pages_add(DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE)); > > return memmap; > } > -- > 2.20.1 > -- Sincerely yours, Mike.