generic: test deadlock on O_DIRECT|O_DSYNC

We had a problem recently where btrfs would deadlock with
O_DIRECT|O_DSYNC because of an unexpected dependency on ->fsync in
iomap.  This was only caught by chance with aiostress, because weirdly
we don't actually test this particular configuration anywhere in
xfstests.  Fix this by adding a basic test that just does
O_DIRECT|O_DSYNC writes.  With this test the box deadlocks right away
with Btrfs, which would have been helpful in finding this issue before
the patches were merged.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/609

@@ -0,0 +1,44 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2020 Josef Bacik.  All Rights Reserved.
+#
+# FS QA Test 609
+#
+# iomap can call generic_write_sync() if we're O_DSYNC, so write a basic test to
+# exercise O_DSYNC so any unsuspecting file systems will get lockdep warnings if
+# their locking isn't compatible.
+#
+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.*
+	rm -rf $TEST_DIR/file
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# Modify as appropriate.
+_supported_fs generic
+_supported_os Linux
+_require_test
+_require_xfs_io_command "pwrite"
+_require_odirect
+
+$XFS_IO_PROG -f -d -s -c "pwrite 0 64k" $TEST_DIR/file | _filter_xfs_io
+
+status=0
+exit

tests/generic/609.out

@@ -0,0 +1,3 @@
+QA output created by 609
+wrote 65536/65536 bytes at offset 0
+XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)

tests/generic/group

@@ -611,3 +611,4 @@
 606 auto attr quick dax
 607 auto attr quick dax
 608 auto attr quick dax
+609 auto quick rw