[PATCH 2/2] btrfs/132: test for crash if btrfs quota disable is killed while waiting on rescan

[Jeff Mahoney <jeffm@suse.com>]

There was a bug in btrfs where the wait for completion of the qgroup
rescan worker could be interrupted, resulting in a crash in the rescan
worker when the quota root goes away.

It is possible to interrupt the wait during file system umount as well,
but effectively impossible to test.  The umount generally succeeds safely
anyway due to other synchronization points.

This issue is resolved by the following patch for the Linux kernel:
"btrfs: waiting on qgroup rescan should not always be interruptible"

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
---
 tests/btrfs/132     | 101 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/132.out |   1 +
 tests/btrfs/group   |   1 +
 3 files changed, 103 insertions(+)
 create mode 100755 tests/btrfs/132
 create mode 100644 tests/btrfs/132.out

diff --git a/tests/btrfs/132 b/tests/btrfs/132
new file mode 100755
index 0000000..3929afa
--- /dev/null
+++ b/tests/btrfs/132
@@ -0,0 +1,101 @@
+#! /bin/bash
+# FS QA Test 132
+#
+# Test for race with signal being received in btrfs_qgroup_disable and
+# the qgroup rescan worker.  The failure case is a crash due to the quota
+# root being released prematurely.
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2016 SUSE.  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 -f $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs btrfs
+_supported_os Linux
+
+# We'll exit with a quota rescan paused
+_require_scratch_nocheck
+
+_require_btrfs
+BTRFS_DEBUG_TREE_PROG="`set_prog_path btrfs-debug-tree`"
+_require_command "$BTRFS_DEBUG_TREE_PROG" btrfs-debug-tree
+
+rm -f $seqres.full
+
+_scratch_mkfs >>$seqres.full 2>&1
+_scratch_mount
+cp -aR /lib/modules/$(uname -r) $SCRATCH_MNT
+
+# A qgroup rescan on an empty or small file system completes nearly
+# immediately.  We need to ensure that it runs long enough that it will
+# be running when the disable ioctl executes.  Snapshots slow down the
+# rescan so we should see the race without a lot of data.  This is an
+# arbitrary number that works on a ramdisk so it should be sufficient
+# for any storage.
+for n in $(seq 1 100); do
+    _run_btrfs_util_prog subvolume snapshot $SCRATCH_MNT $SCRATCH_MNT/$n
+done
+
+sync
+_run_btrfs_util_prog quota enable $SCRATCH_MNT
+
+# _run_btrfs_util_prog runs the command in a subshell
+# so jobs -p and $! don't work
+$BTRFS_UTIL_PROG quota disable $SCRATCH_MNT &
+
+# This is arbitrary as well but worked for me.  The goal is to let the
+# command get into the umount syscall before calling kill but not so far
+# into it that we've already waited for the rescan worker to complete.
+usleep 10000
+jobs=$(jobs -p)
+if kill -0 $jobs 2> /dev/null; then
+	kill -KILL $jobs
+else
+	echo "quota disable command exited too quickly"
+fi
+
+# wait will output the Killed message, so silence that
+wait 2> /dev/null
+_scratch_unmount
+
+# success, all done
+status=0
+exit
diff --git a/tests/btrfs/132.out b/tests/btrfs/132.out
new file mode 100644
index 0000000..06c1d19
--- /dev/null
+++ b/tests/btrfs/132.out
@@ -0,0 +1 @@
+QA output created by 132
diff --git a/tests/btrfs/group b/tests/btrfs/group
index 929fa21..c4e880a 100644
--- a/tests/btrfs/group
+++ b/tests/btrfs/group
@@ -134,3 +134,4 @@
 129 auto quick send
 130 auto clone send
 131 auto quick qgroup
+132 auto quick qgroup
-- 
1.8.5.6


-- 
Jeff Mahoney
SUSE Labs