# 2026-04-21 — Hubris crash loop (thermal + USB drive)

## Summary

[`hubris`](../../../wiki/hosts/hubris.md) hard-locked repeatedly on 2026-04-21 (silent CPU hangs, no panic, no OOM, no MCE). Two contributors identified: idle CPU sitting at ~95 °C on the `performance` governor, and a USB-attached external SSD whose UAS interaction with the AMD USB4/Thunderbolt PCIe tunnel triggered hard locks. CPU thermal addressed via `cpu-epp.service`; drive removed 2026-04-22 as an A/B test. As of 2026-04-28 the host has 3+ days uptime — the drive looks like the primary contributor; `cpu-epp` remains as belt-and-suspenders.

## Timeline

### 2026-04-19 — drive attached
External `Silicon Motion Portable SSD` (vid:pid `090c:2320`) attached for the new restic [backup pipeline](../../../wiki/infrastructure/backups.md). Pre-attach uptime had been 33 days stable.

### 2026-04-19 → 2026-04-21 — first crashes
Two hard crashes in 2.5 days (46 h then 12 h uptime). Kernel logs ended abruptly with routine apparmor entries — no panic, OOM, or MCE — the classic hard-lock signature. Preceded by `uas_eh_abort_handler` storms and xHCI resets on port 6-1.

### 2026-04-21 — crash cadence escalates
23:02 (previous night) → 12:01 the next day. Cadence: 12 h → 43 m → 8 m → 5 m. Stable since the 12:03 boot once `cpu-epp.service` started applying `EPP=balance_power`.

### 2026-04-21 — first set of mitigations applied

- **`cpu-epp.service`** deployed. Sets `scaling_governor=powersave` + EPP=`balance_power` at boot. Drops idle Tctl from ~95 °C → ~60 °C, clocks from 4.4 GHz pinned → 1.1–2 GHz idle.
- **Crash capture**: `/etc/sysctl.d/60-crash-capture.conf` (panic on oops/hardlockup/softlockup/rcu, auto-reboot 10 s), `/etc/modprobe.d/softdog.conf` (`soft_panic=1 soft_margin=60`), `/etc/systemd/system.conf.d/watchdog.conf` (`RuntimeWatchdogSec=15s`).
- **`rasdaemon`** installed (Debian pkg; mcelog is retired) — logs MCE / memory / PCIe AER / thermal events to `/var/lib/rasdaemon/ras-mc_event.db`. Query `ras-mc-ctl --summary`.
- **UAS blacklist** for the drive: `/etc/modprobe.d/usb-storage-quirks.conf` → `options usb-storage quirks=090c:2320:u`. Forces BOT instead of UAS for the SMI bridge.
- **Mount-on-demand** for the drive: `/usr/local/sbin/backup-usb.sh attach|detach|status` toggles `/sys/bus/usb/devices/*/authorized` so the drive is de-authorized when no backup is running.

### 2026-04-22 — recurrence after 30 h 37 m
Same silent-cutoff signature at 18:42:08. Much longer than any pre-`cpu-epp` crash (12 h max), so `cpu-epp` helps but is not sufficient on its own. [claudio-monitor](../../../wiki/infrastructure/monitoring.md) showed healthy runtimes up to 43 s before the hang (no pre-crash degradation). No MCE / no RAS / pstore empty.

### 2026-04-22 — `cpu-epp.service` design bug fixed
Was `After=multi-user.target` + `WantedBy=multi-user.target` — queued behind `pve-guests.service`. The hottest window of every boot (20 LXCs + 1 VM coming up) ran on the `performance` governor. Fixed: now `After=sysinit.target` + `Before=pve-guests.service`.

### 2026-04-22 — drive removed (A/B test)
User physically removed the external USB drive. [Backup timers disabled](../../../wiki/infrastructure/backups.md#status), fstab entry commented, drive de-authorized. Goal: confirm whether the drive + UAS + AMD USB4 PCIe-tunnel interaction is the dominant root cause.

### 2026-04-23 — SSD cooling + thermal pads installed
Cold-boot baseline (3 min uptime): nvme0n1 35 °C composite / sensor1 (controller) **53 °C**; nvme1n1 36 °C composite / both sensors ≤36 °C. Lifetime warning-time counters at install: nvme0n1 709 min warn + 5 min crit; nvme1n1 778 min warn + 45 min crit — both drives had spent real time in thermal warning historically.

#### 2026-04-23 thermal-pad verdict
Resolved (3 h self-paced watch). Steady-state across 17:03 → 19:56 stayed pinned at nvme0 composite 47 °C / sensor1 60–61 °C, nvme1 38–40 °C. Zero new warning-time minutes on either drive. Controller sensor1 at 60-ish is normal idle for M.2 NVMe. **The load-bearing signal is the lifetime warning-time counter, not absolute sensor1** — watch that going forward, not sensor1 threshold.

### 2026-04-28 — A/B test passing so far
3+ days continuous uptime with the drive removed. If uptime now exceeds ~3 days without crash, the drive/PCIe-tunnel interaction is confirmed as the dominant root cause. Will revisit options (different drive, different USB port, different bridge) once stability is firmly established.

### 2026-04-29 — physical relocation
User moved the host to a spot with better airflow. Post-move idle baseline (45 min uptime, light load): Tctl **47.2 °C**, GPU 42 °C, nvme0 composite 34.9 °C / sensor1 32.9 °C, nvme1 composite 38.9 °C / sensor1 52.9 °C, DRAM 34–35.5 °C. Notably nvme0 sensor1 is **27 °C cooler** than the 2026-04-23 thermal-pad steady-state of 60–61 °C. Watch lifetime warning-time counters (`nvme smart-log` → "Warning Comp. Temperature Time") over the next week — flat trend confirms the move helped. Doesn't change the drive-removal A/B test, but reduces residual thermal headroom risk independently.

## Root cause

Two-contributor:
1. **Thermal**: Ryzen 5 7640HS (Phoenix APU) in a passively-cooled GMKtec NucBox sitting at ~95 °C idle under `performance` governor. Mitigated by `cpu-epp.service`. In `amd-pstate=active` mode the governor MUST be `powersave` for EPP values to take effect — `performance` silently ignores them.
2. **Storage**: external USB SSD's UAS keepalive interacts badly with the AMD USB4/Thunderbolt PCIe tunnel. UAS blacklist + mount-on-demand reduced but did not eliminate it. Removing the drive eliminates it (so far).

Background: BIOS 1.02 (latest publicly visible from GMKtec). Vendor not on LVFS so `fwupdmgr` can't update. Non-ECC RAM means memory faults are silent and undetectable except by memtest86+.

## Diagnostic notes

- **Pure hardware hangs leave no trace.** `pstore` stays empty across reboots despite `panic_on_oops/hardlockup/softlockup/rcu` + softdog `soft_panic=1` being configured. The CPU is gone before the kernel can react. Don't waste time on panic traces — use crash cadence + uptime pattern as the diagnostic.
- **First check** if hubris crash-loops again with the same silent-cutoff signature: `cpu-epp.service` is active and `/sys/devices/system/cpu/cpu0/cpufreq/energy_performance_preference` is `balance_power`.
- **Non-ECC RAM means memory faults are silent.** If `cpu-epp` is on and crashes still happen, suspect DIMM next (run memtest86+) and/or try the commented-out `pcie_aspm=off pci=nomsi` workarounds in `/etc/default/grub`.
- **Grub escalation** (`pcie_aspm=off pcie_port_pm=off pci=nomsi`) **deliberately NOT applied** yet to keep the drive-removal test clean. Enable only if crashes continue without the drive.
- `mcelog` is not in Debian 13 repos; `rasdaemon` is the replacement.

## BIOS update path

Checked 2026-04-21. GMKtec is **not on LVFS**, so `fwupdmgr` can't update the NucBox M6 Ultra. BIOS 1.02 (2025-08-06) is the latest publicly visible — GMKtec's download center only publishes Windows drivers, no BIOS listing or changelog. Update path is a `.exe` flasher that needs Windows (would require Windows-To-Go USB on hubris). Before committing to that, email `service@gmktec.com` with the S/N to confirm a newer BIOS / AGESA level actually exists. `fwupd` is now installed, so if GMKtec ever onboards to LVFS, updates appear automatically.

## Mitigations applied

| Mitigation                                | Status   | Notes                                                |
| ----------------------------------------- | -------- | ---------------------------------------------------- |
| `cpu-epp.service` (powersave + balance_power) | Active   | Unit ordering fixed 2026-04-22 to run before guests |
| Crash capture (sysctl + softdog + watchdog) | Active   | Catches everything but pure silicon hangs           |
| `rasdaemon`                               | Active   | Persistent telemetry for MCE / memory / PCIe AER    |
| UAS blacklist for `090c:2320`             | Active (drive currently absent) | `/etc/modprobe.d/usb-storage-quirks.conf` |
| Mount-on-demand (`backup-usb.sh`)         | Active (drive currently absent) | Backup unit `ExecStartPre`/`ExecStopPost` hooks |
| Drive physically removed                  | Active   | A/B test in progress                                 |
| Thermal pads on NVMes                     | Active 2026-04-23 | Steady-state composite 47 °C / sensor1 60 °C |
| `pcie_aspm=off pci=nomsi`                 | NOT applied | Reserved for if crashes recur without the drive    |

## Affected nodes
- [Hubris host](../../../wiki/hosts/hubris.md)
- [Backups (disabled)](../../../wiki/infrastructure/backups.md)
- [Monitoring](../../../wiki/infrastructure/monitoring.md)

## Open questions
- Will the host stay up indefinitely without the drive? (Test ongoing — 3+ days as of 2026-04-28.)
- If yes: which mitigation lets the drive come back? (different drive? different USB port bypassing the hub chain? rear motherboard USB 3 port? alternative bus path?)
- Newer BIOS / AGESA from GMKtec — answered email pending. Without LVFS we need explicit vendor confirmation.
- Memtest86+ pass on the DIMMs — not yet run; deferred until the drive case is closed.
