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Two layers whose cost was a contract to reason about rather than an outcome.
SYSFS_UNKNOWN was a three-valued return five files had to keep apart, and
misreading unknown as absence was silent: a healthy board reported as a firmware
regression. What it guarded is real -- `serial` is served by usb_string_attr,
which takes usb_lock_device_interruptible (v6.12.96 sysfs.c:141-143), the same
lock a wedged usbfs ioctl holds -- so the BOUND stays, on every caller by
default. usb_scan reads `serial` on every device matching the VID, and hil_lock's
controller_of does that on essentially every board, so one wedged DUT would
otherwise stall every worker, not one. What goes is the third value.
read_sysfs now returns str or None, and the question the third value existed to
answer is asked directly instead, by two predicates that say which question they
answer: sysfs_stranded() is process-wide and sticky, for hil_pool_check's footer
("could anything here be the tool losing sight of healthy hardware?"), and
path_stranded(path) is per-device, which is what usbtest needs to tell a DUT
whose `serial` is held under device_lock from one that genuinely left the bus --
that difference decides whether it performs driver-registry writes that take the
uninterruptible device_lock.
Gone: _SysfsUnknown, SYSFS_UNKNOWN, sysfs_blind, sysfs_blind_note,
note_sysfs_strand, the cross-process blindness publishing and its report banner,
usb_scan's (list, bool) return, usbtest's inconclusive abort, _blind_note's slot
in the result tuple, and bounded_open, whose last caller went in the previous
commit.
The strand memo is rewritten around the one invariant that makes it safe to
reuse: it is keyed by the path's kernfs inode, captured BEFORE the read. A
busport does not change when a board returns to the same physical port, so a
path-only blacklist outlives the wedge and hil_pool_check's own recovery flow --
reset, reflash, wait_device polling that busport -- would never look at the
board again. A re-enumeration destroys the kernfs node and makes a new one, so a
changed inode is the all-clear. Two ceilings bound different things: per path
(_PATH_STRAND_MAX) for a board that flaps while still wedged, and per process
(_STRAND_MAX) as a backstop against RLIMIT_NOFILE, counted per PATH rather than
per reader because hil_pool_check runs four poll threads over one bus.
A board the pool guard never reached is now reported as run-aborted rather than
pool-timed-out, and outranks a stale board-locked cell for the same reason the
pool-timeout cell does.
Both predicates answer conservatively where they are consulted before something
irreversible. path_stranded() covers the paths read_sysfs answered None for
WITHOUT reading -- past _STRAND_MAX it declines to start another reader, and
vouching for a path nobody looked at hands usbtest's fail-CLOSED guard a
fabricated all-clear, running remove_id/unbind against a wedged device. usbtest's
startup lookup carries the same caveat hil_test's absent arm already did, because
its stderr is relayed verbatim into the report cell.
strand_note() survives the removal for the same reason master had it: every
caller that can say "not found" needs the same sentence, and the one site left to
re-invent it got missed -- a wedged-but-enumerated printer was reported as an
enumeration failure, sending a maintainer after firmware.
The two predicates are not interchangeable, and usbtest needs both. Its per-case
verdict is per-DUT -- a peer that stranded at case 2 must not make our board
report wedged at case 29 -- but the finally block's cleanup is process-wide:
remove_id plus an unbind of EVERY interface under the driver, including that
peer's, each taking the uninterruptible device_lock. So the verdict uses
path_stranded() and the global cleanup stays gated on sysfs_stranded().
USBTEST_RECOVERY_BUDGET was an independent 250s that could not actually contain
the ladder it reserved for, which is why usbtest.py carried a _time_left() gate
re-deciding before every step -- with a bare '- 35' for costs paid downstream
that nobody could re-derive. Between them the two produced a recovery that
skipped its own steps for most real hangs.
The reserve is now derived from the bounds usbtest itself declares, per flasher
and per target: a probe reset, a reflash, and the Rescue-DP POR plus retry a
wedged RP DAP needs, plus the settles and hil_util.REAP_GRACE for each bounded
step. The Rescue-DP legs are openocd-only and gated on the RP target cfg, and
a stub reset is screened out, so the reserve tracks each board's real ladder
instead of one fleet number: 390s for the two RP boards -- whose ladder the old
250 could not contain, which is exactly why the gates skipped their steps --
190s for the other seventeen probe-reset boards, and 150s for esptool and
lm4flash, whose reset is a no-op. Changing a bound in usbtest moves the
reserve with it, and a unit test asserts it covers the ladder.
With the room actually reserved, the child runs the ladder straight through:
recovery_steps, _time_left, the three per-step gates and the parsed-but-unused
--outer-timeout are gone. What stays is what decides outcomes -- the convoy_safe
gate, reset-before-reflash, the no_op screen so a stub that resets nothing is not
claimed, and wedged_pids() as the arbiter, because a clean flash only proves the
probe wrote the MCU.
hil_util.py 616 -> 514 lines.
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A wedged USB device used to take the whole HIL run with it. Every worker that
touched the poisoned node blocked uninterruptibly, the pool could not be joined,
map_async discarded every board's result, and the job ran to the GitHub ceiling
with no report at all -- while the self-hosted runner's single job slot stayed
occupied and every queued job waited behind it.
Bound the calls a worker makes itself. read_sysfs, bounded_open and run_cmd all
answer within a wall clock; read_sysfs distinguishes "absent" from "unknown",
because a blocked read is not evidence of absence, and caps stranded readers at
four (each costs a thread and an fd for the life of the process) after which the
worker declares itself blind. mtype, the gio unmount, the libmtp session and the
arecord/iperf reaps go through those bounds; the MTP session runs in a disposable
subprocess, since libmtp's ctypes calls block unkillably in D state.
Bound the run. A pool guard (HIL_POOL_TIMEOUT, 60 min) fires before any job
ceiling and still writes a report. When the pool will not shut down, the sweep
kills what the workers spawned -- descendants, not just direct children, since
flashers run in their own session -- confirms each kill actually landed, and
exits early so the runner is freed. Whatever survived is named in the report.
Deliberately shallow past that point. We do not re-scan process groups, prove
pid ownership, or escalate through sudo: a root-owned survivor is reported, not
force-killed, because signalling a pid we cannot prove is ours is the worse
failure, and the job ceiling backstops whatever this misses. A D-state holder
was never killable anyway.
Recover instead of reporting a wedge. A HUNG usbtest case reflashes its own DUT
through its roster flasher, but only where the flasher can reach its probe past
a poisoned node -- openocd pinned to a validated vid_pid, or esptool. Where it
cannot, the run says so rather than reserving budget for a path that cannot fire.
Raise the CI ceilings above the pool guard so the guard fires first and still
writes its report, and pin --retry 1 on every HIL leg: the guard is a flat
constant and does not scale with max_retry, so argparse's default of 3 would
triple the serialized usbtest tail against an unchanged guard.
Split the module: execution in hil_test/hil_flash/usbtest, infrastructure in
helper/ (locking, health, selection, shared bounded IO), and the two matrix
generators into .github/scripts/ -- ci_set_matrix.py sat in workflows/, where
GitHub treats every file as a workflow definition. 193 tests cover the bounded
paths, the kill ladder, the guard and the selector against synthetic /proc trees
and PATH-injected fakes; a real wedge cannot be manufactured on demand.
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