generic: test fsync after unlink

This test is motivated by an fsync issue discovered in btrfs.
The issue was that after fsyncing an inode that got its link count
decremented, and the new link count is greater than zero, after the
fsync log replay the inode's parent directory metadata became
inconsistent - it had a wrong i_size and dangling index entries which
prevented the directory from ever being removed (rmdir always failed
with -ENOTEMPTY, even if the directory had no more child inodes).

The btrfs issue was fixed by the following linux kernel patch:

    Btrfs: fix directory inconsistency after fsync log replay

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

tests/generic/039

@@ -0,0 +1,112 @@
+#! /bin/bash
+# FS QA Test No. 039
+#
+# This test is motivated by an fsync issue discovered in btrfs.
+# The issue was that after fsyncing an inode that got its link count
+# decremented, and the new link count is greater than zero, after the
+# fsync log replay the inode's parent directory metadata became
+# inconsistent - it had a wrong i_size and dangling index entries which
+# prevented the directory from ever being removed (rmdir always failed
+# with -ENOTEMPTY, even if the directory had no more child inodes).
+#
+# The btrfs issue was fixed by the following linux kernel patch:
+#
+#    Btrfs: fix directory inconsistency after fsync log replay
+#
+#-----------------------------------------------------------------------
+# Copyright (C) 2015 SUSE Linux Products GmbH. All Rights Reserved.
+# Author: Filipe Manana <fdmanana@suse.com>
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it would be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write the Free Software Foundation,
+# Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+#-----------------------------------------------------------------------
+#
+
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+here=`pwd`
+tmp=/tmp/$$
+status=1	# failure is the default!
+
+_cleanup()
+{
+	_cleanup_flakey
+}
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+. ./common/dmflakey
+
+# real QA test starts here
+_supported_fs generic
+_supported_os Linux
+_need_to_be_root
+_require_scratch
+_require_dm_flakey
+
+rm -f $seqres.full
+
+_scratch_mkfs >> $seqres.full 2>&1
+
+_init_flakey
+_mount_flakey
+
+# Create a test file with 2 hard links in the same directory.
+mkdir -p $SCRATCH_MNT/a/b
+echo "hello world" > $SCRATCH_MNT/a/b/foo
+ln $SCRATCH_MNT/a/b/foo $SCRATCH_MNT/a/b/bar
+
+# Make sure all metadata and data are durably persisted.
+sync
+
+# Now remove one of the hard links and fsync the inode.
+rm -f $SCRATCH_MNT/a/b/bar
+$XFS_IO_PROG -c "fsync" $SCRATCH_MNT/a/b/foo
+
+# Simulate a crash/power loss. This makes sure the next mount
+# will see an fsync log and will replay that log.
+
+_load_flakey_table $FLAKEY_DROP_WRITES
+_unmount_flakey
+
+_load_flakey_table $FLAKEY_ALLOW_WRITES
+_mount_flakey
+
+# Remove the last hard link of the file and attempt to remove its parent
+# directory - this failed in btrfs because the fsync log and replay code
+# didn't decrement the parent directory's i_size and left dangling directory
+# index entries - this made the btrfs rmdir implementation always fail with
+# the error -ENOTEMPTY.
+#
+# The dangling directory index entries were visible to user space, but it was
+# impossible to do anything on them (unlink, open, read, write, stat, etc)
+# because the inode they pointed to did not exist anymore.
+#
+# The parent directory's metadata inconsistency (stale index entries) was
+# also detected by btrfs' fsck tool, which is run automatically by the fstests
+# framework when the test finishes. The error message reported by fsck was:
+#
+# root 5 inode 259 errors 2001, no inode item, link count wrong
+#   unresolved ref dir 258 index 3 namelen 3 name bar filetype 1 errors 4, no inode ref
+#
+rm -f $SCRATCH_MNT/a/b/*
+rmdir $SCRATCH_MNT/a/b
+rmdir $SCRATCH_MNT/a
+
+echo "Silence is golden"
+status=0
+exit

tests/generic/039.out

@@ -0,0 +1,2 @@
+QA output created by 039
+Silence is golden

tests/generic/group

@@ -41,6 +41,7 @@
 036 auto aio rw stress
 037 metadata auto quick
 038 auto stress
+039 metadata auto quick
 053 acl repair auto quick
 062 attr udf auto quick
 068 other auto freeze dangerous stress