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establishment: unplug reaps like death, so a replug rebinds

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The hot-unplug path (onChildRemoved, a report from a live bus) cleared the
child but left the bound class driver: a process blocked on reports that
will never come, whose stale entry made the matcher's dedupe refuse the
respawn when the device was plugged back in — the same wall the restart
zombie hit, one path over. Unplug now reaps exactly like reporter death.

The usb-hub-unplug case grows the replug: device_del the hub keyboard, then
device_add it back (qmp_sequence); the ordered tail — child removed, reaping,
delegated, ok — can only be satisfied by the second generation, since every
boot keyboard's ok precedes the unplug. Discrimination: without the reap the
replug never rebinds and the case times out (verified by stash run). Hub
family, restart drill, and the two-controller proof all green (8/8).
This commit is contained in:
Daniel Samson
2026-08-09 13:51:07 +01:00
parent 3c9f454398
commit 4a2df587bb
2 changed files with 26 additions and 6 deletions
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test/qemu_test.py
+20 -6
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@@ -955,10 +955,16 @@ CASES = [
"expect": r"(?s)(?=.*hub slot \d+ port \d+ device:.*0x0409)"
r"(?=.*usb-hid-keyboard: ok \(device 3)",
"fail": r"DANOS-TEST-RESULT: FAIL"},
# Hub-downstream disconnect (B4c): device_del the keyboard behind the hub;
# the hub's status-change endpoint reports it, the device is torn down
# (ChildRemoved + Disable Slot). QEMU's hub DOES raise downstream changes
# (unlike root-port hot-plug).
# Hub-downstream disconnect AND replug (B4c + establishment): device_del the
# keyboard behind the hub — the hub's status-change endpoint reports it, the
# device is torn down (ChildRemoved + Disable Slot), and the manager REAPS
# the bound class driver (it blocks on reports that will never come, and its
# stale entry would make the dedupe refuse the respawn). Then device_add
# plugs it back: the re-report re-registers the same identity and the
# matcher spawns a fresh driver, which binds — the ordered tail (reaping →
# child removed → delegated → ok) can only be satisfied by the SECOND
# generation, since the boot keyboards' ok lines all precede the unplug.
# QEMU's hub DOES raise downstream changes (unlike root-port hot-plug).
{"name": "usb-hub-unplug",
"build_case": "usb-hid",
"smp": 4,
@@ -966,9 +972,17 @@ CASES = [
"qemu_extra": ["-device", "qemu-xhci,id=xhci2",
"-device", "usb-hub,bus=xhci2.0,port=1",
"-device", "usb-kbd,bus=xhci2.0,port=1.1,id=dkbd"],
"qmp_after": {"delay": 8, "command": "device_del", "arguments": {"id": "dkbd"}},
"qmp_sequence": [
{"delay": 8, "command": "device_del", "arguments": {"id": "dkbd"}},
{"delay": 14, "command": "device_add",
"arguments": {"driver": "usb-kbd", "bus": "xhci2.0", "port": "1.1", "id": "dkbd2"}},
],
"expect": r"(?s)(?=.*usb-hid-keyboard: ok \(device 3)"
r"(?=.*slot \d+ disconnected)",
r"(?=.*slot \d+ disconnected"
r"[\s\S]*device-manager: child removed"
r"[\s\S]*device-manager: reaping \S*usb-hid-keyboard"
r"[\s\S]*device-manager: delegated device \d+ to /system/drivers/usb-hid-keyboard"
r"[\s\S]*usb-hid-keyboard: ok)",
"fail": r"DANOS-TEST-RESULT: FAIL"},
# The kernel VFS root (M-F): the mount table serves the initrd at /system —
# path resolution, node status/read (an ELF magic), and directory listing,