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=-8.3 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,UNPARSEABLE_RELAY, URIBL_BLOCKED,USER_AGENT_SANE_1 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 68BC7C3A5A6 for ; Wed, 28 Aug 2019 14:24:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2CC4D22CED for ; Wed, 28 Aug 2019 14:24:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="q0qOV458" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726513AbfH1OYQ (ORCPT ); Wed, 28 Aug 2019 10:24:16 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:33850 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726341AbfH1OYP (ORCPT ); Wed, 28 Aug 2019 10:24:15 -0400 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x7SEJc2W082750; Wed, 28 Aug 2019 14:23:36 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : content-transfer-encoding : in-reply-to; s=corp-2019-08-05; bh=vgrDwVHdmJZ9aYJbqbUl1TJIyAPUEDAJ1ALO9+oPAUw=; b=q0qOV458W/bztCNufWPs26s3Ym+GRSQ1ziezYIQ0ZFdTRRngupxVv3OQaCUmcLUtLiLu LnHrBMgGaR7OHU5wxRKNCF1KHDG4YVV4HdudKI68Sli0kgcA0fu0KDZSfyvlEXHxj3+3 rg//5L9oBD/UoXPRXQdeFNrMWzjPQ45kODxgFqxK0NXMFewF8oXglYMYFKMEWoNw34OY 3FYbhLvRoAHcI7/MJ9IxOWjWWowXRCh5CGntTiZ3Cr+64eDmpx27R9t2k2oqIPrtqvLO y0mBeYh+NHIsdnynZPgmhxbcvqC5MH3mKvHtKug+GkznZMFuTdm8stQG185jIyQsFqZE yQ== Received: from aserp3030.oracle.com (aserp3030.oracle.com [141.146.126.71]) by userp2130.oracle.com with ESMTP id 2unu76829k-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 28 Aug 2019 14:23:36 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x7SEN4I9020552; Wed, 28 Aug 2019 14:23:35 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserp3030.oracle.com with ESMTP id 2unduq14tx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 28 Aug 2019 14:23:35 +0000 Received: from abhmp0015.oracle.com (abhmp0015.oracle.com [141.146.116.21]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x7SENY8U012960; Wed, 28 Aug 2019 14:23:34 GMT Received: from localhost (/67.169.218.210) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 28 Aug 2019 07:23:33 -0700 Date: Wed, 28 Aug 2019 07:23:32 -0700 From: "Darrick J. Wong" To: Andreas =?iso-8859-1?Q?Gr=FCnbacher?= Cc: Amir Goldstein , Dave Chinner , jencce.kernel@gmail.com, linux-xfs , overlayfs , Zorro Lang , fstests , linux-fsdevel , Christoph Hellwig , cluster-devel Subject: Re: [PATCH v2 2/2] iomap: partially revert 4721a601099 (simulated directio short read on EFAULT) Message-ID: <20190828142332.GT1037422@magnolia> References: <20181202180832.GR8125@magnolia> <20181202181045.GS8125@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9363 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908280151 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9363 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908280150 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Wed, Aug 21, 2019 at 10:23:49PM +0200, Andreas Grünbacher wrote: > Hi Darrick, > > Am So., 2. Dez. 2018 um 19:13 Uhr schrieb Darrick J. Wong > : > > From: Darrick J. Wong > > > > In commit 4721a601099, we tried to fix a problem wherein directio reads > > into a splice pipe will bounce EFAULT/EAGAIN all the way out to > > userspace by simulating a zero-byte short read. This happens because > > some directio read implementations (xfs) will call > > bio_iov_iter_get_pages to grab pipe buffer pages and issue asynchronous > > reads, but as soon as we run out of pipe buffers that _get_pages call > > returns EFAULT, which the splice code translates to EAGAIN and bounces > > out to userspace. > > > > In that commit, the iomap code catches the EFAULT and simulates a > > zero-byte read, but that causes assertion errors on regular splice reads > > because xfs doesn't allow short directio reads. This causes infinite > > splice() loops and assertion failures on generic/095 on overlayfs > > because xfs only permit total success or total failure of a directio > > operation. The underlying issue in the pipe splice code has now been > > fixed by changing the pipe splice loop to avoid avoid reading more data > > than there is space in the pipe. > > > > Therefore, it's no longer necessary to simulate the short directio, so > > remove the hack from iomap. > > > > Fixes: 4721a601099 ("iomap: dio data corruption and spurious errors when pipes fill") > > Reported-by: Amir Goldstein > > Reviewed-by: Christoph Hellwig > > Signed-off-by: Darrick J. Wong > > --- > > v2: split into two patches per hch request > > --- > > fs/iomap.c | 9 --------- > > 1 file changed, 9 deletions(-) > > > > diff --git a/fs/iomap.c b/fs/iomap.c > > index 3ffb776fbebe..d6bc98ae8d35 100644 > > --- a/fs/iomap.c > > +++ b/fs/iomap.c > > @@ -1877,15 +1877,6 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, > > dio->wait_for_completion = true; > > ret = 0; > > } > > - > > - /* > > - * Splicing to pipes can fail on a full pipe. We have to > > - * swallow this to make it look like a short IO > > - * otherwise the higher splice layers will completely > > - * mishandle the error and stop moving data. > > - */ > > - if (ret == -EFAULT) > > - ret = 0; > > break; > > } > > pos += ret; > > I'm afraid this breaks the following test case on xfs and gfs2, the > two current users of iomap_dio_rw. Hmm, I had kinda wondered if regular pipes still needed this help. Evidently we don't have a lot of splice tests in fstests. :( > Here, the splice system call fails with errno = EAGAIN when trying to > "move data" from a file opened with O_DIRECT into a pipe. > > The test case can be run with option -d to not use O_DIRECT, which > makes the test succeed. > > The -r option switches from reading from the pipe sequentially to > reading concurrently with the splice, which doesn't change the > behavior. > > Any thoughts? This would be great as an xfstest! :) Do you have one ready to go, or should I just make one from the source code? --D > Thanks, > Andreas > > =================================== 8< =================================== > #define _GNU_SOURCE > #include > #include > #include > #include > #include > #include > > #include > #include > #include > #include > #include > > #define SECTOR_SIZE 512 > #define BUFFER_SIZE (150 * SECTOR_SIZE) > > void read_from_pipe(int fd, const char *filename, size_t size) > { > char buffer[SECTOR_SIZE]; > size_t sz; > ssize_t ret; > > while (size) { > sz = size; > if (sz > sizeof buffer) > sz = sizeof buffer; > ret = read(fd, buffer, sz); > if (ret < 0) > err(1, "read: %s", filename); > if (ret == 0) { > fprintf(stderr, "read: %s: unexpected EOF\n", filename); > exit(1); > } > size -= sz; > } > } > > void do_splice1(int fd, const char *filename, size_t size) > { > bool retried = false; > int pipefd[2]; > > if (pipe(pipefd) == -1) > err(1, "pipe"); > while (size) { > ssize_t spliced; > > spliced = splice(fd, NULL, pipefd[1], NULL, size, SPLICE_F_MOVE); > if (spliced == -1) { > if (errno == EAGAIN && !retried) { > retried = true; > fprintf(stderr, "retrying splice\n"); > sleep(1); > continue; > } > err(1, "splice"); > } > read_from_pipe(pipefd[0], filename, spliced); > size -= spliced; > } > close(pipefd[0]); > close(pipefd[1]); > } > > void do_splice2(int fd, const char *filename, size_t size) > { > bool retried = false; > int pipefd[2]; > int pid; > > if (pipe(pipefd) == -1) > err(1, "pipe"); > > pid = fork(); > if (pid == 0) { > close(pipefd[1]); > read_from_pipe(pipefd[0], filename, size); > exit(0); > } else { > close(pipefd[0]); > while (size) { > ssize_t spliced; > > spliced = splice(fd, NULL, pipefd[1], NULL, size, SPLICE_F_MOVE); > if (spliced == -1) { > if (errno == EAGAIN && !retried) { > retried = true; > fprintf(stderr, "retrying splice\n"); > sleep(1); > continue; > } > err(1, "splice"); > } > size -= spliced; > } > close(pipefd[1]); > waitpid(pid, NULL, 0); > } > } > > void usage(const char *argv0) > { > fprintf(stderr, "USAGE: %s [-rd] {filename}\n", basename(argv0)); > exit(2); > } > > int main(int argc, char *argv[]) > { > void (*do_splice)(int fd, const char *filename, size_t size); > const char *filename; > char *buffer; > int opt, open_flags, fd; > ssize_t ret; > > do_splice = do_splice1; > open_flags = O_CREAT | O_TRUNC | O_RDWR | O_DIRECT; > > while ((opt = getopt(argc, argv, "rd")) != -1) { > switch(opt) { > case 'r': > do_splice = do_splice2; > break; > case 'd': > open_flags &= ~O_DIRECT; > break; > default: /* '?' */ > usage(argv[0]); > } > } > > if (optind >= argc) > usage(argv[0]); > filename = argv[optind]; > > printf("%s reader %s O_DIRECT\n", > do_splice == do_splice1 ? "sequential" : "concurrent", > (open_flags & O_DIRECT) ? "with" : "without"); > > buffer = aligned_alloc(SECTOR_SIZE, BUFFER_SIZE); > if (buffer == NULL) > err(1, "aligned_alloc"); > > fd = open(filename, open_flags, 0666); > if (fd == -1) > err(1, "open: %s", filename); > > memset(buffer, 'x', BUFFER_SIZE); > ret = write(fd, buffer, BUFFER_SIZE); > if (ret < 0) > err(1, "write: %s", filename); > if (ret != BUFFER_SIZE) { > fprintf(stderr, "%s: short write\n", filename); > exit(1); > } > > ret = lseek(fd, 0, SEEK_SET); > if (ret != 0) > err(1, "lseek: %s", filename); > > do_splice(fd, filename, BUFFER_SIZE); > > if (unlink(filename) == -1) > err(1, "unlink: %s", filename); > > return 0; > } > =================================== 8< ===================================