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=ham 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 CBF83C3F2D8 for ; Wed, 4 Mar 2020 10:47:40 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7BE8820732 for ; Wed, 4 Mar 2020 10:47:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=126.com header.i=@126.com header.b="FLwMrJsD" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7BE8820732 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 1382E6B0003; Wed, 4 Mar 2020 05:47:39 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 0C26C6B0005; Wed, 4 Mar 2020 05:47:39 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id ECC596B0006; Wed, 4 Mar 2020 05:47:38 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0038.hostedemail.com [216.40.44.38]) by kanga.kvack.org (Postfix) with ESMTP id D1BB16B0003 for ; Wed, 4 Mar 2020 05:47:38 -0500 (EST) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 45284180AD801 for ; Wed, 4 Mar 2020 10:47:38 +0000 (UTC) X-FDA: 76557353796.29.knife33_7cbd3ab614419 X-HE-Tag: knife33_7cbd3ab614419 X-Filterd-Recvd-Size: 6176 Received: from m15-113.126.com (m15-113.126.com [220.181.15.113]) by imf49.hostedemail.com (Postfix) with ESMTP for ; Wed, 4 Mar 2020 10:47:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=126.com; s=s110527; h=From:Subject:Date:Message-Id; bh=IeCdyAGFwXp3ZJWoz2 7XzqKXoULD6qM3z6NhawmdYlI=; b=FLwMrJsDJPv6HNAMsaGYL/PvWgyW9o9yHK q6HXkdW7AM1QvSpze8XFkN/SeWjbG/ha9btTU56lE+M8PInQu6ULLwfn3eq822dk SrDWA4Xs8tW1x/7nTQS0J5+PPhE+3YyYJI01BS7C3e3bbWs+6NOra1lDgTAZ/hKQ zcoZxa7tE= Received: from 192.168.137.251 (unknown [112.10.84.98]) by smtp3 (Coremail) with SMTP id DcmowAC3EAc8h19e2h4DCA--.2331S3; Wed, 04 Mar 2020 18:47:26 +0800 (CST) From: Xianting Tian To: akpm@linux-foundation.org, willy@infradead.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] mm/filemap.c: clear page error before actual read Date: Wed, 4 Mar 2020 05:47:24 -0500 Message-Id: <1583318844-22971-1-git-send-email-xianting_tian@126.com> X-Mailer: git-send-email 1.8.3.1 X-CM-TRANSID:DcmowAC3EAc8h19e2h4DCA--.2331S3 X-Coremail-Antispam: 1Uf129KBjvJXoWxZF1rGr4DAw1UAryrCrW7Jwb_yoWrAFWDpr ZxK3WDKr4DGrnrCan2q3Z7Ar1rGrnrAay5ZayrW343Zwn8XF1fW34xCFyjg345Gr1FyFWx Xr4FqF98Cr9YqaDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07jTc_-UUUUU= X-Originating-IP: [112.10.84.98] X-CM-SenderInfo: h0ld03plqjs3xldqqiyswou0bp/1tbi3B7cpFpD+S1DOAAAsM 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 | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/filemap.c b/mm/filemap.c index 1784478..77c370d 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2823,6 +2823,14 @@ static struct page *do_read_cache_page(struct address_space *mapping, unlock_page(page); goto out; } + + /* + * 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); goto filler; out: -- 1.8.3.1