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=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 026DAC3F2D1 for ; Tue, 3 Mar 2020 15:43:43 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A63D620863 for ; Tue, 3 Mar 2020 15:43:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=126.com header.i=@126.com header.b="MdUVlzkH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A63D620863 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=126.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 3CDC26B0005; Tue, 3 Mar 2020 10:43:42 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 357736B0006; Tue, 3 Mar 2020 10:43:42 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 21F186B0007; Tue, 3 Mar 2020 10:43:42 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0190.hostedemail.com [216.40.44.190]) by kanga.kvack.org (Postfix) with ESMTP id 04DEB6B0005 for ; Tue, 3 Mar 2020 10:43:42 -0500 (EST) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id BB2CA16933 for ; Tue, 3 Mar 2020 15:43:41 +0000 (UTC) X-FDA: 76554471042.14.beam16_bc2fd6aca300 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin14.hostedemail.com (Postfix) with ESMTP id E471318027FEE for ; Tue, 3 Mar 2020 15:41:22 +0000 (UTC) X-HE-Tag: beam16_bc2fd6aca300 X-Filterd-Recvd-Size: 6165 Received: from m15-111.126.com (m15-111.126.com [220.181.15.111]) by imf28.hostedemail.com (Postfix) with ESMTP for ; Tue, 3 Mar 2020 15:41:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=126.com; s=s110527; h=From:Subject:Date:Message-Id; bh=tucUIJDzJdQGxz9VTj FcydNy10+WnttpeLoZcEBMltQ=; b=MdUVlzkHdC8380MTa2fYYAkFJsXF+auvL2 eKSbs8lwCvuTyS4bbkBxbv7oVTrKj664IikyAExAECfT+AwVekXwaWTp4OQmnJON 2sKVW0+Mj49WdHqMP0SONHd00OgUEVlBdly2gScfHZ3sINP4ClHwkowKj64jgQmb kIN75OuQU= Received: from 192.168.137.250 (unknown [112.10.84.98]) by smtp1 (Coremail) with SMTP id C8mowACnO+E_c15e55mzBw--.46087S3; Tue, 03 Mar 2020 23:09:51 +0800 (CST) From: Xianting Tian To: akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] mm/filemap.c: clear page error before actual read Date: Tue, 3 Mar 2020 10:09:50 -0500 Message-Id: <1583248190-18123-1-git-send-email-xianting_tian@126.com> X-Mailer: git-send-email 1.8.3.1 X-CM-TRANSID:C8mowACnO+E_c15e55mzBw--.46087S3 X-Coremail-Antispam: 1Uf129KBjvJXoWxZF1rGr4DAw1UAryrCrW7Jwb_yoWrAFWDpr ZxK3WDKr4DGrnrCan2q3Z7Ar1rJrsrAay5ZayrW343Zwn8JF1fW34xCFyjg345Gr1FyFWx XF45tas8CrnYqaDanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07j9yCXUUUUU= X-Originating-IP: [112.10.84.98] X-CM-SenderInfo: h0ld03plqjs3xldqqiyswou0bp/1tbi7QTbpFpD+F-zFQAAsO 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: Mount failure issue happens under the scenario: Application forked dozens of threads to mount the same number of cramfs images separately in docker, but several mounts failed with high probability. Mount failed due to the checking result of the page(read from the superblock of loop dev) is not uptodate after wait_on_page_locked(page) returned in function cramfs_read: wait_on_page_locked(page); if (!PageUptodate(page)) { ... } The reason of the checking result of the page not uptodate: systemd-udevd read the loopX dev before mount, because the status of loopX is Lo_unbound at this time, so loop_make_request directly trigger the calling of io_end handler end_buffer_async_read, which called SetPageError(page). So It caused the page can't be set to uptodate in function end_buffer_async_read: if(page_uptodate && !PageError(page)) { SetPageUptodate(page); } Then mount operation is performed, it used the same page which is just accessed by systemd-udevd above, Because this page is not uptodate, it will launch a actual read via submit_bh, then wait on this page by calling wait_on_page_locked(page). When the I/O of the page done, io_end handler end_buffer_async_read is called, because no one cleared the page error(during the whole read path of mount), which is caused by systemd-udevd reading, so this page is still in "PageError" status, which can't be set to uptodate in function end_buffer_async_read, then caused mount failure. But sometimes mount succeed even through systemd-udeved read loopX dev just before, The reason is systemd-udevd launched other loopX read just between step 3.1 and 3.2, the steps as below: 1, loopX dev default status is Lo_unbound; 2, systemd-udved read loopX dev (page is set to PageError); 3, mount operation 1) set loopX status to Lo_bound; ==>systemd-udevd read loopX dev<== 2) read loopX dev(page has no error) 3) mount succeed As the loopX dev status is set to Lo_bound after step 3.1, so the other loopX dev read by systemd-udevd will go through the whole I/O stack, part of the call trace as below: SYS_read vfs_read do_sync_read blkdev_aio_read generic_file_aio_read do_generic_file_read: ClearPageError(page); mapping->a_ops->readpage(filp, page); here, mapping->a_ops->readpage() is blkdev_readpage. In latest kernel, some function name changed, the call trace as below: blkdev_read_iter generic_file_read_iter generic_file_buffered_read: /* * A previous I/O error may have been due to temporary * failures, eg. mutipath errors. * Pg_error will be set again if readpage fails. */ ClearPageError(page); /* Start the actual read. The read will unlock the page*/ error=mapping->a_ops->readpage(flip, page); We can see ClearPageError(page) is called before the actual read, then the read in step 3.2 succeed. This patch is to add the calling of ClearPageError just before the actual read of read path of cramfs mount. Without the patch, the call trace as below when performing cramfs mount: do_mount cramfs_read cramfs_blkdev_read read_cache_page do_read_cache_page: filler(data, page); or mapping->a_ops->readpage(data, page); With the patch, the call trace as below when performing mount: do_mount cramfs_read cramfs_blkdev_read read_cache_page: do_read_cache_page: ClearPageError(page); <== new add filler(data, page); or mapping->a_ops->readpage(data, page); With the patch, mount operation trigger the calling of ClearPageError(page) before the actual read, the page has no error if no additional page error happen when I/O done. Signed-off-by: Xianting Tian --- mm/filemap.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/mm/filemap.c b/mm/filemap.c index 1784478..d65428f 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2755,6 +2755,13 @@ static struct page *do_read_cache_page(struct address_space *mapping, } filler: + /* + * A previous I/O error may have been due to temporary + * failures. + * Clear page error before actual read, PG_error will be + * set again if read page fails. + */ + ClearPageError(page); if (filler) err = filler(data, page); else -- 1.8.3.1