The testcase simply creates a 64G image with 1M clusters, generates a list
of 1M aligned offsets and feeds aio_write commands with those offsets to
qemu-io run with '--aio native --nocache'.  Then we check the data
written at each of the offsets.  Before the previous commit this could
result into a race within the preallocation filter which would zeroize
some clusters after actually writing data to them.

Note: the test doesn't fail in 100% cases as there's a race involved,
but the failures are pretty consistent so it should be good enough for
detecting the problem.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 tests/qemu-iotests/298     | 49 ++++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/298.out |  4 ++--
 2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/tests/qemu-iotests/298 b/tests/qemu-iotests/298
index 09c9290711..b7126e9e15 100755
--- a/tests/qemu-iotests/298
+++ b/tests/qemu-iotests/298
@@ -20,8 +20,10 @@
 
 import os
 import iotests
+import random
 
 MiB = 1024 * 1024
+GiB = MiB * 1024
 disk = os.path.join(iotests.test_dir, 'disk')
 overlay = os.path.join(iotests.test_dir, 'overlay')
 refdisk = os.path.join(iotests.test_dir, 'refdisk')
@@ -176,5 +178,52 @@ class TestTruncate(iotests.QMPTestCase):
         self.do_test('off', '150M')
 
 
+class TestPreallocAsyncWrites(iotests.QMPTestCase):
+    def setUp(self):
+        # Make sure we get reproducible write patterns on each run
+        random.seed(42)
+        iotests.qemu_img_create('-f', iotests.imgfmt, disk, '-o',
+                                f'cluster_size={MiB},lazy_refcounts=on',
+                                str(64 * GiB))
+
+    def tearDown(self):
+        os.remove(disk)
+
+    def test_prealloc_async_writes(self):
+        def gen_write_pattern():
+            n = 0
+            while True:
+                yield '-P 0xaa' if n else '-z'
+                n = 1 - n
+
+        def gen_read_pattern():
+            n = 0
+            while True:
+                yield '-P 0xaa' if n else '-P 0x00'
+                n = 1 - n
+
+        requests = 2048 # Number of write/read requests to feed to qemu-io
+        total_clusters = 64 * 1024 # 64G / 1M
+
+        wpgen = gen_write_pattern()
+        rpgen = gen_read_pattern()
+
+        offsets = random.sample(range(0, total_clusters), requests)
+        aio_write_cmds = [f'aio_write {next(wpgen)} {off}M 1M' for off in offsets]
+        read_cmds = [f'read {next(rpgen)} {off}M 1M' for off in offsets]
+
+        proc = iotests.QemuIoInteractive('--aio', 'native', '--nocache',
+                                         '--image-opts', drive_opts)
+        for cmd in aio_write_cmds:
+            proc.cmd(cmd)
+        proc.close()
+
+        proc = iotests.QemuIoInteractive('-f', iotests.imgfmt, disk)
+        for cmd in read_cmds:
+            out = proc.cmd(cmd)
+            self.assertFalse('Pattern verification failed' in str(out))
+        proc.close()
+
+
 if __name__ == '__main__':
     iotests.main(supported_fmts=['qcow2'], required_fmts=['preallocate'])
diff --git a/tests/qemu-iotests/298.out b/tests/qemu-iotests/298.out
index fa16b5ccef..6323079e08 100644
--- a/tests/qemu-iotests/298.out
+++ b/tests/qemu-iotests/298.out
@@ -1,5 +1,5 @@
-.............
+..............
 ----------------------------------------------------------------------
-Ran 13 tests
+Ran 14 tests
 
 OK
-- 
2.39.3