btrfs: Incorrect exclusive reference number after file clone.

[Problem]
Since commit fcebe4562dec83b3f8d308 ("Btrfs: rework qgroup accounting"),
quota data update is delayed after delayed_ref calculation, and lacks
correct protection to detect root reference which shouldn't be counted
in current sequence number but already written into extent backref.

This makes exclusive reference not decreased correctly and give incorrect
result.

[Test procedure]
1. Create a btrfs with 3 subvolumes, quota enabled and rescanned.
2. Create a file in 1st subvolume
3. Clone the file to 2nd and 3rd subvolume
4. Sync the fs to reflect the changes in qgroup.
5. Check the qgroup data

[Expected result]
None of the subvolume has exclusive reference to the file.

[Actual result]
The first subvolume still have exclusive reference to the file.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

tests/btrfs/091

@@ -0,0 +1,102 @@
+#! /bin/bash
+# FS QA Test No. 091
+#
+# Test for incorrect exclusive reference count after cloning file
+# between subvolumes.
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2015 Fujitsu. All Rights Reserved.
+#
+# 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!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+    rm -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# real QA test starts here
+
+_need_to_be_root
+_supported_fs btrfs
+_supported_os Linux
+_require_scratch
+_require_cp_reflink
+
+rm -f $seqres.full
+
+# use largest node/leaf size (64K) to allow the test to be run on arch with
+# page size > 4k.
+NODESIZE=65536
+SUPPORT_NOINODE_CACHE="yes"
+
+run_check _scratch_mkfs "--nodesize $NODESIZE"
+
+# inode cache will also take space in fs tree, disable them to get consistent
+# result.
+# discard error output since we will check return value manually.
+_scratch_mount "-o noinode_cache" 2> /dev/null
+
+# Check for old kernel which doesn't support 'noinode_cache' mount option
+if [ $? -ne 0 ]; then
+	support_noinode_cache="no"
+	run_check _scratch_mount
+fi
+
+_run_btrfs_util_prog subvolume create $SCRATCH_MNT/subv1
+_run_btrfs_util_prog subvolume create $SCRATCH_MNT/subv2
+_run_btrfs_util_prog subvolume create $SCRATCH_MNT/subv3
+
+_run_btrfs_util_prog quota enable $SCRATCH_MNT
+_run_btrfs_util_prog quota rescan -w $SCRATCH_MNT
+
+# if we don't support noinode_cache mount option, then we should double check
+# whether inode cache is enabled before executing the real test payload.
+if [ $SUPPORT_NOINODE_CACHE == "no" ]; then
+	EMPTY_SIZE=`$BTRFS_UTIL_PROG qgroup show $units $SCRATCH_MNT | \
+		$SED_PROG -n '/[0-9]/p' | $AWK_PROG '{print $2}' | head -n1`
+	if [ $EMPTY_SIZE != $NODESIZE ]; then
+		_notrun "Kernel doesn't support to disable inode cache"
+	fi
+fi
+
+$XFS_IO_PROG -f -c "pwrite 0 256K" $SCRATCH_MNT/subv1/file1 | _filter_xfs_io
+cp --reflink $SCRATCH_MNT/subv1/file1 $SCRATCH_MNT/subv2/file1
+cp --reflink $SCRATCH_MNT/subv1/file1 $SCRATCH_MNT/subv3/file1
+
+# Current btrfs use tree search ioctl to show quota, which will only show info
+# in commit tree. So need to sync to update the qgroup commit tree.
+sync
+
+units=`_btrfs_qgroup_units`
+$BTRFS_UTIL_PROG qgroup show $units $SCRATCH_MNT | $SED_PROG -n '/[0-9]/p' | \
+	$AWK_PROG '{print $2" "$3}'
+
+# success, all done
+status=0
+exit

tests/btrfs/091.out

@@ -0,0 +1,7 @@
+QA output created by 091
+wrote 262144/262144 bytes at offset 0
+XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+65536 65536
+327680 65536
+327680 65536
+327680 65536

tests/btrfs/group

@@ -92,3 +92,4 @@
 087 auto quick send
 088 auto quick metadata
 090 auto quick metadata
+091 auto quick qgroup