I/O test 308 is flaky under AWS CI runners, failed to see size increase from fallocate
## Host environment
- Operating system: Unknown
- OS/kernel version: Unknown
- Architecture: x86_64
- QEMU flavor: qemu-system-x86_64
- QEMU version: e89049b3ba5f1f0468bc0d294173345597514a1b
- QEMU command line:
```
check -qcow2 308
check -qed 308
```
## Description of problem
The I/O test 308 is showing failures when run under QEMU's private AWS CI runners, while working fine on the CI shared runners
```
115/147 block-qcow2-optional+block-slow - qemu:io-qcow2-308 ERROR 7.14s exit status 1
>>> RUST_BACKTRACE=1 PYTHON=/builds/qemu-project/qemu/build/pyvenv/bin/python3 UBSAN_OPTIONS=halt_on_error=1:abort_on_error=1:print_summary=1:print_stacktrace=1 MESON_TEST_ITERATION=1 LD_LIBRARY_PATH=/builds/qemu-project/qemu/build/subprojects/libvfio-user/lib MSAN_OPTIONS=halt_on_error=1:abort_on_error=1:print_summary=1:print_stacktrace=1 ASAN_OPTIONS=halt_on_error=1:abort_on_error=1:print_summary=1 MALLOC_PERTURB_=110 /builds/qemu-project/qemu/build/pyvenv/bin/python3 /builds/qemu-project/qemu/build/../tests/qemu-iotests/check -tap -qcow2 308 --source-dir /builds/qemu-project/qemu/tests/qemu-iotests --build-dir /builds/qemu-project/qemu/build/tests/qemu-iotests
――――――――――――――――――――――――――――――――――――― ✀ ―――――――――――――――――――――――――――――――――――――
stderr:
--- /builds/qemu-project/qemu/tests/qemu-iotests/308.out
+++ /builds/qemu-project/qemu/build/scratch/qcow2-file-308/308.out.bad
@@ -146,7 +146,8 @@
--- Resize export ---
(OK: Lengths of export and original are the same)
OK: Post-truncate image size is as expected
-OK: Disk usage grew with fallocate
+ERROR: Disk usage did not grow despite fallocate:
+68358144 => 68358144
0+1 records in
0+1 records out
(test program exited with status code 1)
```
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