vmm_tests: fix serial hangup race in the IOAPIC interrupt-remapping check - #4082
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Pull request overview
This PR addresses intermittent failures in the PCIe IOMMU interrupt-remapping tests by eliminating a race where systemd’s serial-getty@ttyS0.service can vhangup /dev/ttyS0 during the test’s serial-write loop, causing write() to fail with EIO.
Changes:
- Stop
serial-getty@ttyS0.serviceon systemd-based Linux guests before writing to/dev/ttyS0, preventing vhangup-inducedEIOfailures mid-loop. - Make the serial-write loop fail-fast by adding
set -e, ensuring any failed iteration is surfaced instead of being silently ignored.
jstarks
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Jul 29, 2026
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amd_iommu_mixed_topology / intel_vtd_multi_segment intermittently fail with sh: 1: echo: echo: I/O error.
Root cause. The test generates serial IRQs by writing to ttyS0, which is the guest console with serial-getty@ttyS0.service on it. That unit is Type=idle + TTYVHangup=yes, so agetty isn't exec'd until systemd's boot job queue drains — and when it runs it vhangups the tty, failing any in-flight write() with EIO. Pipette starts before boot finishes, so the test can land in that window. In run 30466090198 the EIO hit 4 ms after Finished cloud-final.service.
Fix. Use ttyS1 instead, as there's no getty attached to it.
Also adds set -e to the write loop — a for loop's status is only its last iteration's, so failed writes were being silently discarded. Only safe with the fix, as it makes the test ~32x more sensitive.