s390 intermittent test failure in qemu:block / io-qcow2-copy-before-write

[Peter Maydell]

There seems to be an intermittent failure on the s390 host in
the qemu:block / io-qcow2-copy-before-write test:
https://gitlab.com/qemu-project/qemu/-/jobs/4737819873

The log says the test was expecting to do some reading
and writing but got an unexpected 'permission denied'
error on the read. Any idea why this might happen ?

768/835 qemu:block / io-qcow2-copy-before-write ERROR 12.05s exit status 1
>>> PYTHON=/home/gitlab-runner/builds/-LCfcJ2T/0/qemu-project/qemu/build/pyvenv/bin/python3
>>>  MALLOC_PERTURB_=101 
>>> /home/gitlab-runner/builds/-LCfcJ2T/0/qemu-project/qemu/build/pyvenv/bin/python3
>>>  
>>> /home/gitlab-runner/builds/-LCfcJ2T/0/qemu-project/qemu/build/../tests/qemu-iotests/check
>>>  -tap -qcow2 copy-before-write --source-dir 
>>> /home/gitlab-runner/builds/-LCfcJ2T/0/qemu-project/qemu/tests/qemu-iotests 
>>> --build-dir 
>>> /home/gitlab-runner/builds/-LCfcJ2T/0/qemu-project/qemu/build/tests/qemu-iotests
――――――――――――――――――――――――――――――――――――― ✀ ―――――――――――――――――――――――――――――――――――――
stderr:
--- 
/home/gitlab-runner/builds/-LCfcJ2T/0/qemu-project/qemu/tests/qemu-iotests/tests/copy-before-write.out
+++ 
/home/gitlab-runner/builds/-LCfcJ2T/0/qemu-project/qemu/build/scratch/qcow2-file-copy-before-write/copy-before-write.out.bad
@@ -1,5 +1,21 @@
-....
+...F
+======================================================================
+FAIL: test_timeout_break_snapshot (__main__.TestCbwError)
+----------------------------------------------------------------------
+Traceback (most recent call last):
+ File 
"/home/gitlab-runner/builds/-LCfcJ2T/0/qemu-project/qemu/tests/qemu-iotests/tests/copy-before-write",
line 210, in test_timeout_break_snapshot
+ self.assertEqual(log, """\
+AssertionError: 'wrot[195 chars]read 1048576/1048576 bytes at offset
0\n1 MiB,[46 chars]c)\n' != 'wrot[195 chars]read failed: Permission
denied\n'
+ wrote 524288/524288 bytes at offset 0
+ 512 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+ wrote 524288/524288 bytes at offset 524288
+ 512 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
++ read failed: Permission denied
+- read 1048576/1048576 bytes at offset 0
+- 1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+
----------------------------------------------------------------------
Ran 4 tests
-OK
+FAILED (failures=1)
(test program exited with status code 1)
――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――

Same failure, previous job:

https://gitlab.com/qemu-project/qemu/-/jobs/4736463062

This one's a "Failed to get write lock" in io-qcow2-161:

https://gitlab.com/qemu-project/qemu/-/jobs/4734846533

(I'm not sure whether there's something up with the s390
at the moment -- it seems to be producing these odd
failures, not always in the iotests. I'm wondering if
it's just running too slowly and we're hitting race
conditions in test cases.)

thanks
-- PMM