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 X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 63C7EC5DF62 for ; Wed, 6 Nov 2019 06:10:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 26197214D8 for ; Wed, 6 Nov 2019 06:10:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=fb.com header.i=@fb.com header.b="aWd2ZJxE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726191AbfKFGKH (ORCPT ); Wed, 6 Nov 2019 01:10:07 -0500 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:36264 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725806AbfKFGKG (ORCPT ); Wed, 6 Nov 2019 01:10:06 -0500 Received: from pps.filterd (m0044012.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id xA66A2Jt030235 for ; Tue, 5 Nov 2019 22:10:05 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-type; s=facebook; bh=ZNEK/2HxCUlHQJ5GI8dDxUQNL+Ty25u3PZmn8QkENtk=; b=aWd2ZJxEnjwy9mWP0mLdjqoDoSC7tBju9kJkVFyv3qvQvMZjsR88H8yginXnZ7BXVcCV WMElqehGQJuHsd0eri/rkc0B5sV6c0rNvhUzLg27TdaQozq6uwNwsdLJiR/PxCiSgZ/8 0uwlkvTDYVlkPfr3i1jUxnWsVvWtjf34y4A= Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com with ESMTP id 2w3ddeugq7-7 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Tue, 05 Nov 2019 22:10:05 -0800 Received: from 2401:db00:30:6012:face:0:17:0 (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:83::4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1713.5; Tue, 5 Nov 2019 22:09:53 -0800 Received: by devbig006.ftw2.facebook.com (Postfix, from userid 4523) id DAB0162E36EB; Tue, 5 Nov 2019 22:09:51 -0800 (PST) Smtp-Origin-Hostprefix: devbig From: Song Liu Smtp-Origin-Hostname: devbig006.ftw2.facebook.com To: , , CC: , , , , Song Liu , Johannes Weiner , Hugh Dickins Smtp-Origin-Cluster: ftw2c04 Subject: [PATCH v5 1/2] mm,thp: recheck each page before collapsing file THP Date: Tue, 5 Nov 2019 22:09:29 -0800 Message-ID: <20191106060930.2571389-2-songliubraving@fb.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20191106060930.2571389-1-songliubraving@fb.com> References: <20191106060930.2571389-1-songliubraving@fb.com> X-FB-Internal: Safe MIME-Version: 1.0 Content-Type: text/plain X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,18.0.572 definitions=2019-11-06_01:2019-11-05,2019-11-06 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 lowpriorityscore=0 spamscore=0 mlxscore=0 suspectscore=0 mlxlogscore=999 phishscore=0 clxscore=1015 priorityscore=1501 bulkscore=0 impostorscore=0 adultscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1908290000 definitions=main-1911060064 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In collapse_file(), for !is_shmem case, current check cannot guarantee the locked page is up-to-date. Specifically, xas_unlock_irq() should not be called before lock_page() and get_page(); and it is necessary to recheck PageUptodate() after locking the page. With this bug and CONFIG_READ_ONLY_THP_FOR_FS=y, madvise(HUGE)'ed .text may contain corrupted data. This is because khugepaged mistakenly collapses some not up-to-date sub pages into a huge page, and assumes the huge page is up-to-date. This will NOT corrupt data in the disk, because the page is read-only and never written back. Fix this by properly checking PageUptodate() after locking the page. This check replaces "VM_BUG_ON_PAGE(!PageUptodate(page), page);". Also, move PageDirty() check after locking the page. Current khugepaged should not try to collapse dirty file THP, because it is limited to read-only .text. The only case we hit a dirty page here is when the page hasn't been written since write. Bail out and retry when this happens. syzbot reported bug on previous version of this patch. Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") Reported-by: syzbot+efb9e48b9fbdc49bb34a@syzkaller.appspotmail.com Cc: Johannes Weiner Cc: Kirill A. Shutemov Cc: Hugh Dickins Cc: William Kucharski Cc: Andrew Morton Signed-off-by: Song Liu --- [songliubraving@fb.com: v4] Link: http://lkml.kernel.org/r/20191022191006.411277-1-songliubraving@fb.com [songliubraving@fb.com: fix deadlock in collapse_file()] Link: http://lkml.kernel.org/r/20191028221414.3685035-1-songliubraving@fb.com Link: http://lkml.kernel.org/r/20191018180345.4188310-1-songliubraving@fb.com [songliubraving@fb.com: flush file for !is_shmem PageDirty() case in collapse_file()] https://lkml.kernel.org/linux-mm/20191030200736.3455046-1-songliubraving@fb.com/ --- mm/khugepaged.c | 28 ++++++++++++++++------------ 1 file changed, 16 insertions(+), 12 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 0a1b4b484ac5..40215795d641 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1601,17 +1601,6 @@ static void collapse_file(struct mm_struct *mm, result = SCAN_FAIL; goto xa_unlocked; } - } else if (!PageUptodate(page)) { - xas_unlock_irq(&xas); - wait_on_page_locked(page); - if (!trylock_page(page)) { - result = SCAN_PAGE_LOCK; - goto xa_unlocked; - } - get_page(page); - } else if (PageDirty(page)) { - result = SCAN_FAIL; - goto xa_locked; } else if (trylock_page(page)) { get_page(page); xas_unlock_irq(&xas); @@ -1626,7 +1615,12 @@ static void collapse_file(struct mm_struct *mm, * without racing with truncate. */ VM_BUG_ON_PAGE(!PageLocked(page), page); - VM_BUG_ON_PAGE(!PageUptodate(page), page); + + /* make sure the page is up to date */ + if (unlikely(!PageUptodate(page))) { + result = SCAN_FAIL; + goto out_unlock; + } /* * If file was truncated then extended, or hole-punched, before @@ -1642,6 +1636,16 @@ static void collapse_file(struct mm_struct *mm, goto out_unlock; } + if (!is_shmem && PageDirty(page)) { + /* + * khugepaged only works on read-only fd, so this + * page is dirty because it hasn't been flushed + * since first write. + */ + result = SCAN_FAIL; + goto out_unlock; + } + if (isolate_lru_page(page)) { result = SCAN_DEL_PAGE_LRU; goto out_unlock; -- 2.17.1