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=-3.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 92873C432C3 for ; Sat, 16 Nov 2019 01:34:56 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 559BF2073B for ; Sat, 16 Nov 2019 01:34:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="Y3XVrqV6" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 559BF2073B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 07D386B000E; Fri, 15 Nov 2019 20:34:56 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 02EA06B0010; Fri, 15 Nov 2019 20:34:55 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EADC96B0266; Fri, 15 Nov 2019 20:34:55 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0089.hostedemail.com [216.40.44.89]) by kanga.kvack.org (Postfix) with ESMTP id D63856B000E for ; Fri, 15 Nov 2019 20:34:55 -0500 (EST) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id 94595181AEF1E for ; Sat, 16 Nov 2019 01:34:55 +0000 (UTC) X-FDA: 76160421750.28.rake52_ddb1f9ef6e09 X-HE-Tag: rake52_ddb1f9ef6e09 X-Filterd-Recvd-Size: 4639 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf24.hostedemail.com (Postfix) with ESMTP for ; Sat, 16 Nov 2019 01:34:55 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id F413420801; Sat, 16 Nov 2019 01:34:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573868094; bh=S3USzezoQRj5jMc6OjFk6hQVEuacae2TqlBoCR5WOVc=; h=Date:From:To:Subject:From; b=Y3XVrqV66xhxpI7WxPQBzjO18cD/R/mkORqycXjmUAlgu76bh5B7lHY4P8P24hRYx lqEIRCqKO0Tl6SE/6VruWgP2K464q47GOv8P1zLXVMYHVhow4EViVdnP/yfhU6Ycw9 p7SaRcsDBpLFeduu4ULhZGtlprM/WIZ4LNVTa/JY= Date: Fri, 15 Nov 2019 17:34:53 -0800 From: akpm@linux-foundation.org To: akpm@linux-foundation.org, hannes@cmpxchg.org, hughd@google.com, kirill.shutemov@linux.intel.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, songliubraving@fb.com, torvalds@linux-foundation.org, william.kucharski@oracle.com Subject: [patch 07/11] mm,thp: recheck each page before collapsing file THP Message-ID: <20191116013453.px7Eggwu0%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 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: Song Liu Subject: mm,thp: recheck each page before collapsing file THP 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. Link: http://lkml.kernel.org/r/20191106060930.2571389-2-songliubraving@fb.com Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") Signed-off-by: Song Liu Reported-by: syzbot+efb9e48b9fbdc49bb34a@syzkaller.appspotmail.com Cc: Johannes Weiner Cc: Kirill A. Shutemov Cc: Hugh Dickins Cc: William Kucharski Signed-off-by: Andrew Morton --- mm/khugepaged.c | 28 ++++++++++++++++------------ 1 file changed, 16 insertions(+), 12 deletions(-) --- a/mm/khugepaged.c~mmthp-recheck-each-page-before-collapsing-file-thp +++ a/mm/khugepaged.c @@ -1602,17 +1602,6 @@ static void collapse_file(struct mm_stru 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); @@ -1627,7 +1616,12 @@ static void collapse_file(struct mm_stru * 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 @@ -1643,6 +1637,16 @@ static void collapse_file(struct mm_stru 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; _