From: Stefan Hajnoczi <[email protected]>
The 093 throttling test submits twice as many requests as the throttle
limit in order to ensure that we reach the limit. The remaining
requests are left in-flight at the end of each test iteration.
Commit 452589b6b47e8dc6353df257fc803dfc1383bed8 ("vl.c/exit: pause cpus
before closing block devices") exposed a hang in 093. This happens
because requests are still in flight when QEMU terminates but
QEMU_CLOCK_VIRTUAL time is frozen. bdrv_drain_all() hangs forever since
throttled requests cannot complete.
Step the clock at the end of each test iteration so in-flight requests
actually finish. This solves the hang and is cleaner than leaving tests
in-flight.
Note that this could also be "fixed" by disabling throttling when drives
are closed in QEMU. That approach has two issues:
1. We must drain requests before disabling throttling, so the hang
cannot be easily avoided!
2. Any time QEMU disables throttling internally there is a chance that
malicious users can abuse the code path to bypass throttling limits.
Therefore it makes more sense to fix the test case than to modify QEMU.
Signed-off-by: Stefan Hajnoczi <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Eric Blake <[email protected]>
---
tests/qemu-iotests/093 | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/tests/qemu-iotests/093 b/tests/qemu-iotests/093
index 2ed393a548..ef3997206b 100755
--- a/tests/qemu-iotests/093
+++ b/tests/qemu-iotests/093
@@ -133,6 +133,10 @@ class ThrottleTestCase(iotests.QMPTestCase):
self.assertTrue(check_limit(params['iops_rd'], rd_iops))
self.assertTrue(check_limit(params['iops_wr'], wr_iops))
+ # Allow remaining requests to finish. We submitted twice as many to
+ # ensure the throttle limit is reached.
+ self.vm.qtest("clock_step %d" % ns)
+
# Connect N drives to a VM and test I/O in all of them
def test_all(self):
params = {"bps": 4096,
--
2.13.5
