generic: test race between appending AIO DIO and fallocate

Dave Chinner reports[1] that an appending AIO DIO write to the second
block of a zero-length file and an fallocate request to the first block
of the same file can race to set isize, with the user-visible end result
that the file size is set incorrectly to one block long.  Write a small
test to reproduce the results.

[1] https://lore.kernel.org/linux-xfs/20191029100342.GA41131@bfoster/T/

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/586

@@ -0,0 +1,44 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (c) 2019, Oracle and/or its affiliates.  All Rights Reserved.
+#
+# FS QA Test No. 586
+#
+# Race an appending aio dio write to the second block of a file while
+# simultaneously fallocating to the first block.  Make sure that we end up
+# with a two-block file.
+
+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.* $testfile
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+
+# real QA test starts here
+_supported_os Linux
+_supported_fs generic
+_require_aiodio "aio-dio-append-write-fallocate-race"
+_require_test
+_require_xfs_io_command "falloc"
+
+rm -f $seqres.full
+
+testfile=$TEST_DIR/test-$seq
+$AIO_TEST $testfile 100 >> $seqres.full
+
+echo Silence is golden.
+# success, all done
+status=0
+exit

tests/generic/586.out

@@ -0,0 +1,2 @@
+QA output created by 586
+Silence is golden.

tests/generic/group

@@ -588,3 +588,4 @@
 583 auto quick encrypt
 584 auto quick encrypt
 585 auto rename
+586 auto quick rw prealloc