[PATCH] fstests: btrfs: Test if btrfs will panic when mounting a partially balanced fs

[Qu Wenruo <wqu@suse.com>]

There are two regressions that when mounting a partially balance btrfs
after v5.1 kernel:
- Kernel NULL pointer dereference at mount time
- Kernel BUG_ON() just after mount

The kernel fixes are:
"btrfs: qgroup: Check if @bg is NULL to avoid NULL pointer
 dereference"
"btrfs: reloc: Also queue orphan reloc tree for cleanup to
 avoid BUG_ON()"

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 tests/btrfs/188     | 94 +++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/188.out |  2 +
 tests/btrfs/group   |  1 +
 3 files changed, 97 insertions(+)
 create mode 100755 tests/btrfs/188
 create mode 100644 tests/btrfs/188.out

diff --git a/tests/btrfs/188 b/tests/btrfs/188
new file mode 100755
index 00000000..f43be007
--- /dev/null
+++ b/tests/btrfs/188
@@ -0,0 +1,94 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2019 SUSE Linux Products GmbH.  All Rights Reserved.
+#
+# FS QA Test 188
+#
+# Test if btrfs mount will hit the following bugs when mounting
+# a fs going through partial balance:
+# - NULL pointer dereference
+# - Kernel BUG_ON()
+#
+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
+. ./common/dmlogwrites
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs btrfs
+_supported_os Linux
+_require_scratch
+# and we need extra device as log device
+_require_log_writes
+
+nr_files=512				# enough metadata to bump tree height
+file_size=2048				# small enough to be inlined
+
+_log_writes_init $SCRATCH_DEV
+_log_writes_mkfs >> $seqres.full 2>&1
+
+_log_writes_mount
+$BTRFS_UTIL_PROG quota enable $SCRATCH_MNT >> $seqres.full
+$BTRFS_UTIL_PROG quota rescan -w $SCRATCH_MNT >> $seqres.full
+
+# Create enough metadata for later balance
+for ((i = 0; i < $nr_files; i++)); do
+	_pwrite_byte 0xcd 0 $file_size $SCRATCH_MNT/file_$i > /dev/null
+done
+
+# Ensure we write all data/metadata back to disk so that later
+# balance will do real I/O
+sync
+
+# Balance metadata so we will have at least one transaction committed with
+# valid reloc tree, and hopefully an orphan reloc tree.
+$BTRFS_UTIL_PROG balance start -f -m $SCRATCH_MNT >> $seqres.full
+_log_writes_unmount
+_log_writes_remove
+
+cur=$(_log_writes_find_next_fua 0)
+echo "cur=$cur" >> $seqres.full
+while [ ! -z "$cur" ]; do
+	_log_writes_replay_log_range $cur $SCRATCH_DEV >> $seqref.full
+
+	# If the fs contains valid reloc tree and kernel is not patched,
+	# we'll hit a NULL pointer dereference
+	# Or if it contains orphan reloc tree and kernel is unpatched,
+	# we'll hit a BUG_ON()
+	_scratch_mount
+	_scratch_unmount
+
+	# Don't trigger fsck here, as relocation get paused,
+	# at that transistent state, qgroup number may differ
+	# and cause false alert.
+
+	prev=$cur
+	cur=$(_log_writes_find_next_fua $(($cur + 1)))
+	[ -z "$cur" ] && break
+done
+
+echo "Silence is golden"
+
+# success, all done
+status=0
+exit
diff --git a/tests/btrfs/188.out b/tests/btrfs/188.out
new file mode 100644
index 00000000..6f23fda0
--- /dev/null
+++ b/tests/btrfs/188.out
@@ -0,0 +1,2 @@
+QA output created by 188
+Silence is golden
diff --git a/tests/btrfs/group b/tests/btrfs/group
index 44ee0dd9..16a7c31e 100644
--- a/tests/btrfs/group
+++ b/tests/btrfs/group
@@ -190,3 +190,4 @@
 185 volume
 186 auto quick send volume
 187 auto send dedupe clone balance
+188 auto quick replay
-- 
2.21.0