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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 15FCEC43334 for ; Mon, 27 Jun 2022 22:27:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242579AbiF0W10 (ORCPT ); Mon, 27 Jun 2022 18:27:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59604 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240399AbiF0W1X (ORCPT ); Mon, 27 Jun 2022 18:27:23 -0400 Received: from mail105.syd.optusnet.com.au (mail105.syd.optusnet.com.au [211.29.132.249]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 8ED7518357 for ; Mon, 27 Jun 2022 15:27:22 -0700 (PDT) Received: from dread.disaster.area (pa49-181-2-147.pa.nsw.optusnet.com.au [49.181.2.147]) by mail105.syd.optusnet.com.au (Postfix) with ESMTPS id 7FAC010EA992; Tue, 28 Jun 2022 08:27:21 +1000 (AEST) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1o5xCS-00BqDO-68; Tue, 28 Jun 2022 08:27:20 +1000 Date: Tue, 28 Jun 2022 08:27:20 +1000 From: Dave Chinner To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org, allison.henderson@oracle.com Subject: Re: [PATCH 3/3] xfs: dont treat rt extents beyond EOF as eofblocks to be cleared Message-ID: <20220627222720.GF227878@dread.disaster.area> References: <165628102728.4040423.16023948770805941408.stgit@magnolia> <165628104422.4040423.6482533913763183686.stgit@magnolia> <20220627013731.GB227878@dread.disaster.area> <20220627051649.GD227878@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.4 cv=VuxAv86n c=1 sm=1 tr=0 ts=62ba2ec9 a=ivVLWpVy4j68lT4lJFbQgw==:117 a=ivVLWpVy4j68lT4lJFbQgw==:17 a=kj9zAlcOel0A:10 a=JPEYwPQDsx4A:10 a=VwQbUJbxAAAA:8 a=20KFwNOVAAAA:8 a=7-415B0cAAAA:8 a=t6_JvATAxVzgssUnmgcA:9 a=CjuIK1q_8ugA:10 a=AjGcO6oz07-iQ99wixmX:22 a=biEYGPWJfzWAr4FL6Ov7:22 Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Mon, Jun 27, 2022 at 01:59:32PM -0700, Darrick J. Wong wrote: > On Mon, Jun 27, 2022 at 03:16:49PM +1000, Dave Chinner wrote: > > On Sun, Jun 26, 2022 at 08:57:25PM -0700, Darrick J. Wong wrote: > > > On Mon, Jun 27, 2022 at 11:37:31AM +1000, Dave Chinner wrote: > > > > On Sun, Jun 26, 2022 at 03:04:04PM -0700, Darrick J. Wong wrote: > > > > > From: Darrick J. Wong > > > > > > > > > > On a system with a realtime volume and a 28k realtime extent, > > > > > generic/491 fails because the test opens a file on a frozen filesystem > > > > > and closing it causes xfs_release -> xfs_can_free_eofblocks to > > > > > mistakenly think that the the blocks of the realtime extent beyond EOF > > > > > are posteof blocks to be freed. Realtime extents cannot be partially > > > > > unmapped, so this is pointless. Worse yet, this triggers posteof > > > > > cleanup, which stalls on a transaction allocation, which is why the test > > > > > fails. > > > > > > > > > > Teach the predicate to account for realtime extents properly. > > > > > > > > > > Signed-off-by: Darrick J. Wong > > > > > --- > > > > > fs/xfs/xfs_bmap_util.c | 2 ++ > > > > > 1 file changed, 2 insertions(+) > > > > > > > > > > > > > > > diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c > > > > > index 52be58372c63..85e1a26c92e8 100644 > > > > > --- a/fs/xfs/xfs_bmap_util.c > > > > > +++ b/fs/xfs/xfs_bmap_util.c > > > > > @@ -686,6 +686,8 @@ xfs_can_free_eofblocks( > > > > > * forever. > > > > > */ > > > > > end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)XFS_ISIZE(ip)); > > > > > + if (XFS_IS_REALTIME_INODE(ip) && mp->m_sb.sb_rextsize > 1) > > > > > + end_fsb = roundup_64(end_fsb, mp->m_sb.sb_rextsize); > > > > > last_fsb = XFS_B_TO_FSB(mp, mp->m_super->s_maxbytes); > > > > > if (last_fsb <= end_fsb) > > > > > return false; > > > > > > > > Ok, that works. > > > > Reviewed-by: Dave Chinner > > > > > > > > > > However, I was looking at xfs_can_free_eofblocks() w.r.t. freeze a > > > > couple of days ago and wondering why there isn't a freeze/RO state > > > > check in xfs_can_free_eofblocks(). Shouldn't we have one here so > > > > that we never try to run xfs_free_eofblocks() on RO/frozen > > > > filesystems regardless of unexpected state/alignment issues? > > > > > > I asked myself that question too. I found three callers of this > > > predicate: > > > > > > 1. fallocate, which should have obtained freeze protection > > > > *nod* > > > > > 2. inodegc, which should never be running when we get to the innermost > > > freeze protection level > > > > So inodegc could still do IO here on a read-only fs? > > Correct. > > > > 3. xfs_release, which doesn't take freeze protection at all. Either it > > > needs to take freeze protection so that xfs_free_eofblocks can't get > > > stuck in xfs_trans_alloc, or we'd need to modify xfs_trans_alloc to > > > sb_start_intwrite_trylock > > > > That looks to me like it is simply a case of replacing the > > !xfs_is_readonly() check in xfs_release() with a > > !xfs_fs_writeable(mp, SB_FREEZE_WRITE) check and we shouldn't have > > to touch anythign else, right? > > I think there would still be a race if we did that -- I don't see > anything in __fput that prohibits another thread from initiating a > freeze after the release process calls _can_free_eofblocks but before > the actual call to _free_eofblocks. Yup, the probability of that happening is pretty small, and there's every chance it could have got stuck on something else racing with the freeze. In reality, I don't think that blocking in ->release on freeze is inherently bad - it will just wait until the filesystem is thawed and then continue on. i.e. just because the test hangs on closing a fd on a frozen fs doesn't mean that the freeze mechanism is broken in any way.... > Hm. How often would we have a readonly fd pointing to a file that has > posteof blocks? I suppose this could happen if the system was extending > a file, crashed, and then someone remounted, opened a ro fd, and then > closed and froze the fs at the same time...? Snapshots. Open files at freeze time will result in post-eof blocks existing in the snapshot. Mount the snapshot read-only ..... and that's what the read-only check in xfs_release() catches...... Cheers, Dave. -- Dave Chinner david@fromorbit.com