xfstests ext4 305: test read /proc/fs/ext4/<dev>/mb_groups while the fs is being unmounted

Regression test for commit:
9559996 ext4: remove mb_groups before tearing down the buddy_cache

Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Rich Johnston <rjohnston@sgi.com>
[rjohnston@sgi.com renumbered test to next in group sequence] 
Signed-off-by: Rich Johnston <rjohnston@sgi.com>

tests/ext4/305

@@ -0,0 +1,74 @@
+#! /bin/bash
+# FS QA Test No. 305
+#
+# Regression test for commit:
+# 9559996 ext4: remove mb_groups before tearing down the buddy_cache
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2013 Red Hat, Inc.  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"
+
+PIDS=""
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+    cd /
+    kill $PIDS >/dev/null 2>&1
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# real QA test starts here
+_supported_fs ext4
+_supported_os Linux
+
+_require_scratch
+
+rm -f $seq.full
+echo "Silence is golden"
+
+DEV_BASENAME=$(basename $(readlink -f $SCRATCH_DEV))
+echo "Start test on device $SCRATCH_DEV, basename $DEV_BASENAME" >$seq.full
+_scratch_mkfs >>$seq.full 2>&1
+
+while true;do
+	mount $SCRATCH_DEV $SCRATCH_MNT
+	umount $SCRATCH_DEV
+done &
+PIDS=$!
+
+while true;do
+	cat /proc/fs/ext4/$DEV_BASENAME/mb_groups > /dev/null 2>&1
+done &
+PIDS="$PIDS $!"
+
+# sleep for 180s, in most cases a buggy kernel could hit BUG_ON within 3 minutes
+sleep 180
+
+# no BUG_ON, all done
+kill $PIDS >/dev/null 2>&1
+wait
+status=0
+exit

tests/ext4/305.out

@@ -0,0 +1,2 @@
+QA output created by 305
+Silence is golden

tests/ext4/group

@@ -8,4 +8,4 @@
 302 aio dangerous ioctl rw stress
 303 aio dangerous ioctl rw stress
 304 aio dangerous ioctl rw stress
-
+305 auto