From patchwork Tue Mar 22 21:46:11 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 12789235 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]) by smtp.lore.kernel.org (Postfix) with ESMTP id C7AA4C433EF for ; Tue, 22 Mar 2022 21:46:15 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 586456B0152; Tue, 22 Mar 2022 17:46:15 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5342E6B0153; Tue, 22 Mar 2022 17:46:15 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 423D46B0154; Tue, 22 Mar 2022 17:46:15 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0124.hostedemail.com [216.40.44.124]) by kanga.kvack.org (Postfix) with ESMTP id 32D056B0152 for ; Tue, 22 Mar 2022 17:46:15 -0400 (EDT) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id C3D211827C179 for ; Tue, 22 Mar 2022 21:46:14 +0000 (UTC) X-FDA: 79273355868.30.6CA71BC Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by imf22.hostedemail.com (Postfix) with ESMTP id 59DB3C002D for ; Tue, 22 Mar 2022 21:46:14 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 4BC30B81D77; Tue, 22 Mar 2022 21:46:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 09E2AC340EC; Tue, 22 Mar 2022 21:46:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1647985572; bh=1ms0A4CRfbE+q+WFuovPaSOgayD/+vzxjQilvcPcAH4=; h=Date:To:From:In-Reply-To:Subject:From; b=jhKGz1weAcvN1OjR4QHCsvWBLJ56SZz2uJxcpHltSp0LprHZZDx4wHWEDkCHVTYMV vz+UqA0RbTzggObouoddRUjH4xCgGx+X0Rz9GB+nZ4AiPPwf1DZgzhf6vUhLOvRusy RlWy5BTRfV3+/e68FlE/ZhwC7CeA6zawpEI6qPq8= Date: Tue, 22 Mar 2022 14:46:11 -0700 To: ziy@nvidia.com,shy828301@gmail.com,rcampbell@nvidia.com,kirill.shutemov@linux.intel.com,hughd@google.com,akpm@linux-foundation.org,patches@lists.linux.dev,linux-mm@kvack.org,mm-commits@vger.kernel.org,torvalds@linux-foundation.org,akpm@linux-foundation.org From: Andrew Morton In-Reply-To: <20220322143803.04a5e59a07e48284f196a2f9@linux-foundation.org> Subject: [patch 151/227] mm/thp: refix __split_huge_pmd_locked() for migration PMD Message-Id: <20220322214612.09E2AC340EC@smtp.kernel.org> Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=jhKGz1we; spf=pass (imf22.hostedemail.com: domain of akpm@linux-foundation.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none X-Stat-Signature: zo7nj4do7egjzn8qgouwmpjcbcea399p X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 59DB3C002D X-HE-Tag: 1647985574-109996 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Hugh Dickins Subject: mm/thp: refix __split_huge_pmd_locked() for migration PMD Migration entries do not contribute to a page's reference count: move __split_huge_pmd_locked()'s page_ref_add() into pmd_migration's else block (along with the page_count() check - a page is quite likely to have reference count frozen to 0 when a migration entry is found). This will fix a very rare anonymous memory leak, after a split_huge_pmd() raced with an anon split_huge_page() or an anon THP migrate_pages(): since the wrongly raised refcount stopped the page (perhaps small, perhaps huge, depending on when the race hit) from ever being freed. At first I thought there were worse risks, from prematurely unfreezing a frozen page: but now think that would only affect page cache pages, which do not come this way (except for anonymous pages in swap cache, perhaps). Link: https://lkml.kernel.org/r/84792468-f512-e48f-378c-e34c3641e97@google.com Fixes: ec0abae6dcdf ("mm/thp: fix __split_huge_pmd_locked() for migration PMD") Signed-off-by: Hugh Dickins Reviewed-by: Yang Shi Cc: Ralph Campbell Cc: Zi Yan Cc: "Kirill A. Shutemov" Signed-off-by: Andrew Morton --- mm/huge_memory.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/mm/huge_memory.c~mm-thp-refix-__split_huge_pmd_locked-for-migration-pmd +++ a/mm/huge_memory.c @@ -2055,9 +2055,9 @@ static void __split_huge_pmd_locked(stru young = pmd_young(old_pmd); soft_dirty = pmd_soft_dirty(old_pmd); uffd_wp = pmd_uffd_wp(old_pmd); + VM_BUG_ON_PAGE(!page_count(page), page); + page_ref_add(page, HPAGE_PMD_NR - 1); } - VM_BUG_ON_PAGE(!page_count(page), page); - page_ref_add(page, HPAGE_PMD_NR - 1); /* * Withdraw the table only after we mark the pmd entry invalid.