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xfs_getbmap assert

To: xfs@xxxxxxxxxxx
Subject: xfs_getbmap assert
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Mon, 7 Nov 2011 05:30:37 -0500
User-agent: Mutt/1.5.21 (2010-09-15)
With Dmitris fsstress updates I can hit the following assert fairly
regularly:

[11904.943956] XFS: Assertion failed: ((iflags & BMV_IF_DELALLOC) != 0) ||
(map[i].br_startblock != DELAYSTARTBLOCK), file:
/home/hch/work/linux-2.6/fs/xfs/xfs_bmap.c, line: 5604

which means we get an delalloc extent back from FIEMAP/GETBMAP despite
asking for a flush beforehand.  While we hold the iolock over the call
and thus exclude new buffered writers from appearing that doesn't
prevent shared writeable mmaps from creating new delalloc extents.

I don't think this actually is a real issue, and a workaround would
be extremly hard.  For now I've just remove the assert in my tree:


Index: xfs/fs/xfs/xfs_bmap.c
===================================================================
--- xfs.orig/fs/xfs/xfs_bmap.c  2011-11-05 09:02:24.410021945 +0100
+++ xfs/fs/xfs/xfs_bmap.c       2011-11-05 09:03:54.036494235 +0100
@@ -5600,8 +5600,6 @@ xfs_getbmap(
                                XFS_FSB_TO_BB(mp, map[i].br_blockcount);
                        out[cur_ext].bmv_unused1 = 0;
                        out[cur_ext].bmv_unused2 = 0;
-                       ASSERT(((iflags & BMV_IF_DELALLOC) != 0) ||
-                             (map[i].br_startblock != DELAYSTARTBLOCK));
                         if (map[i].br_startblock == HOLESTARTBLOCK &&
                            whichfork == XFS_ATTR_FORK) {
                                /* came to the end of attribute fork */

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