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, USER_AGENT_SANE_1 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 75D6FCA9EB9 for ; Tue, 29 Oct 2019 04:19:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 38CE72086A for ; Tue, 29 Oct 2019 04:19:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="IcTH6Qdr" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730480AbfJ2ETZ (ORCPT ); Tue, 29 Oct 2019 00:19:25 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:57522 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727608AbfJ2ETY (ORCPT ); Tue, 29 Oct 2019 00:19:24 -0400 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x9T4JLEM003015; Tue, 29 Oct 2019 04:19:21 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 : in-reply-to; s=corp-2019-08-05; bh=pRyHZviNz1P360ZPDGyg4+pKKYLYpOdHNXffbVPWZA4=; b=IcTH6QdrmzW3JkJFqyokfH6XdcXN1/EH+x35guGcfBhxJWRksoeB5eTSCBZpuyKQMxGl qqDDGIl1npGcx0vslF/G/IvSrEjhduYvSdFQ0OP68DLOG3PCxsBwzZKFzqIp9KVm8YRm L5p+4vdpX7LmQ72WmWd+Imj7XkzwZvV3C4yFRVzohysHPNfvMjf6VVHGZtabAEhTVsJT ZOb5DKfa7J4fbFgdIJteVS1BISz43691owdLz9i2KRQtqwhfO4EtC2GFPVdwQZhMyGj4 XPd22UgCyv4VNNDh+LH+1obJkaOOH/TMsF9TOQED4UHwl/N4AEy8bxVVEWrwzkVGXft4 Cw== Received: from aserp3030.oracle.com (aserp3030.oracle.com [141.146.126.71]) by userp2120.oracle.com with ESMTP id 2vvumfb31y-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 29 Oct 2019 04:19:16 +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 x9T4IETL010955; Tue, 29 Oct 2019 04:19:15 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by aserp3030.oracle.com with ESMTP id 2vwam078wq-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 29 Oct 2019 04:19:15 +0000 Received: from abhmp0006.oracle.com (abhmp0006.oracle.com [141.146.116.12]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x9T4JB0r007728; Tue, 29 Oct 2019 04:19:12 GMT Received: from localhost (/10.159.156.71) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 28 Oct 2019 21:19:11 -0700 Date: Mon, 28 Oct 2019 21:19:08 -0700 From: "Darrick J. Wong" To: Dave Chinner Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH] xfs: properly serialise fallocate against AIO+DIO Message-ID: <20191029041908.GB15222@magnolia> References: <20191029034850.8212-1-david@fromorbit.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191029034850.8212-1-david@fromorbit.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9424 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=2 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1910290045 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9424 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1910290045 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Tue, Oct 29, 2019 at 02:48:50PM +1100, Dave Chinner wrote: > From: Dave Chinner > > AIO+DIO can extend the file size on IO completion, and it holds > no inode locks while the IO is in flight. Therefore, a race > condition exists in file size updates if we do something like this: > > aio-thread fallocate-thread > > lock inode > submit IO beyond inode->i_size > unlock inode > ..... > lock inode > break layouts > if (off + len > inode->i_size) > new_size = off + len > ..... > inode_dio_wait() > > ..... > completes > inode->i_size updated > inode_dio_done() > .... > > > if (new_size) > xfs_vn_setattr(inode, new_size) > > > Yup, that attempt to extend the file size in the fallocate code > turns into a truncate - it removes the whatever the aio write > allocated and put to disk, and reduced the inode size back down to > where the fallocate operation ends. > > Fundamentally, xfs_file_fallocate() not compatible with racing > AIO+DIO completions, so we need to move the inode_dio_wait() call > up to where the lock the inode and break the layouts. > > Secondly, storing the inode size and then using it unchecked without > holding the ILOCK is not safe; we can only do such a thing if we've > locked out and drained all IO and other modification operations, > which we don't do initially in xfs_file_fallocate. > > It should be noted that some of the fallocate operations are > compound operations - they are made up of multiple manipulations > that may zero data, and so we may need to flush and invalidate the > file multiple times during an operation. However, we only need to > lock out IO and other space manipulation operations once, as that > lockout is maintained until the entire fallocate operation has been > completed. > > Signed-off-by: Dave Chinner > --- > fs/xfs/xfs_bmap_util.c | 8 +------- > fs/xfs/xfs_file.c | 30 ++++++++++++++++++++++++++++++ > fs/xfs/xfs_ioctl.c | 1 + > 3 files changed, 32 insertions(+), 7 deletions(-) > > diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c > index fb31d7d6701e..dea68308fb64 100644 > --- a/fs/xfs/xfs_bmap_util.c > +++ b/fs/xfs/xfs_bmap_util.c > @@ -1040,6 +1040,7 @@ xfs_unmap_extent( > goto out_unlock; > } > > +/* Caller must first wait for the completion of any pending DIOs if required. */ > int > xfs_flush_unmap_range( > struct xfs_inode *ip, > @@ -1051,9 +1052,6 @@ xfs_flush_unmap_range( > xfs_off_t rounding, start, end; > int error; > > - /* wait for the completion of any pending DIOs */ > - inode_dio_wait(inode); Does xfs_reflink_remap_prep still need this function to call inode_dio_wait before zapping the page cache prior to reflinking into an existing file? > - > rounding = max_t(xfs_off_t, 1 << mp->m_sb.sb_blocklog, PAGE_SIZE); > start = round_down(offset, rounding); > end = round_up(offset + len, rounding) - 1; > @@ -1085,10 +1083,6 @@ xfs_free_file_space( > if (len <= 0) /* if nothing being freed */ > return 0; > > - error = xfs_flush_unmap_range(ip, offset, len); > - if (error) > - return error; > - > startoffset_fsb = XFS_B_TO_FSB(mp, offset); > endoffset_fsb = XFS_B_TO_FSBT(mp, offset + len); > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c > index 525b29b99116..865543e41fb4 100644 > --- a/fs/xfs/xfs_file.c > +++ b/fs/xfs/xfs_file.c > @@ -817,6 +817,36 @@ xfs_file_fallocate( > if (error) > goto out_unlock; > > + /* > + * Must wait for all AIO to complete before we continue as AIO can > + * change the file size on completion without holding any locks we > + * currently hold. We must do this first because AIO can update both > + * the on disk and in memory inode sizes, and the operations that follow > + * require the in-memory size to be fully up-to-date. > + */ > + inode_dio_wait(inode); > + > + /* > + * Now AIO and DIO has drained we flush and (if necessary) invalidate > + * the cached range over the first operation we are about to run. > + * > + * We care about zero and collapse here because they both run a hole > + * punch over the range first. Because that can zero data, and the range > + * of invalidation for the shift operations is much larger, we still do > + * the required flush for collapse in xfs_prepare_shift(). > + * > + * Insert has the same range requirements as collapse, and we extend the > + * file first which can zero data. Hence insert has the same > + * flush/invalidate requirements as collapse and so they are both > + * handled at the right time by xfs_prepare_shift(). > + */ > + if (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE | > + FALLOC_FL_COLLAPSE_RANGE)) { Er... "Insert has the same requirements as collapse", but we don't test for that here? Also ... xfs_prepare_shift handles flushing for both collapse and insert range, but we still have to flush here for collapse? I think the third paragraph of the comment is just confusing me more. Does the following describe what's going on? "Insert range has the same range [should this be "page cache flushing"?] requirements as collapse. Because we can zero data as part of extending the file size, we skip the flush here and let the flush in xfs_prepare_shift take care of invalidating the page cache." ? --D > + error = xfs_flush_unmap_range(ip, offset, len); > + if (error) > + goto out_unlock; > + } > + > if (mode & FALLOC_FL_PUNCH_HOLE) { > error = xfs_free_file_space(ip, offset, len); > if (error) > diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c > index 287f83eb791f..800f07044636 100644 > --- a/fs/xfs/xfs_ioctl.c > +++ b/fs/xfs/xfs_ioctl.c > @@ -623,6 +623,7 @@ xfs_ioc_space( > error = xfs_break_layouts(inode, &iolock, BREAK_UNMAP); > if (error) > goto out_unlock; > + inode_dio_wait(inode); > > switch (bf->l_whence) { > case 0: /*SEEK_SET*/ > -- > 2.24.0.rc0 >