xfs: ensure that we don't crash when freeing the ag reservations on a ro mount

Christoph Hellwig discovered that the kernel crashed trying to free
the refcount btree per-ag reservation on a ro mount (because we don't
create the reservation except for rw mounts and ro->rw remounts).  So,
test this to make sure we never do that again. :)

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

tests/xfs/247

@@ -0,0 +1,57 @@
+#! /bin/bash
+# FS QA Test No. 247
+#
+# Mount a reflink/rmap filesystem ro (so the per-AG reservation isn't
+# created) and unmount, to ensure that we free correctly.
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2016, Oracle and/or its affiliates.  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()
+{
+    cd /
+    rm -rf $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+. ./common/reflink
+
+# real QA test starts here
+_supported_os Linux
+_supported_fs xfs
+_require_scratch_reflink
+
+rm -f $seqres.full
+
+echo "Format and mount"
+_scratch_mkfs > $seqres.full 2>&1
+_scratch_mount -o ro >> $seqres.full 2>&1
+
+# success, all done
+status=0
+exit

tests/xfs/247.out

@@ -0,0 +1,2 @@
+QA output created by 247
+Format and mount

tests/xfs/group

@@ -244,6 +244,7 @@
 244 auto quota quick
 245 auto quick clone
 246 auto quick clone
+247 auto quick clone
 250 auto quick rw prealloc metadata
 252 auto quick prealloc
 253 auto quick