Public bug reported:
## Summary
Kernel 6.8.0-147 (noble, installed 2026-10-13) introduced a severe regression in
how often a latent HP firmware ACPI Embedded-Controller mutex bug is triggered
on
an HP EliteBook 860 G10. On 6.8.0-146 the deadlock occurs roughly once every few
days; on 6.8.0-147 it occurs multiple times per day, sometimes within ~10
minutes
of boot, hard-locking systemd (PID 1) and requiring SysRq REISUB. Reverting to
6.8.0-146 restores normal (rare deadlock) behaviour.
## Hardware
- HP EliteBook 860 16 inch G10 Notebook PC
- BIOS: HP V70 Ver. 01.12.00, 2026-02-04 (latest available)
- CPU: Intel (Raptor Lake), i915 integrated graphics
## Root cause vs regression
- Root cause is an HP firmware/AML bug: a thread acquires the ACPI `[ECMX]`
Embedded-Controller mutex via `\_SB.AC._PSR` (AC-adapter power-source read)
and
never releases it. This is HP's to fix and is not kernel-introduced.
- The REGRESSION is that 6.8.0-147 triggers this firmware race far more often
than
6.8.0-146, turning a rare annoyance into an unusable machine.
## Log signature (at moment of each deadlock)
kernel: ACPI Error: Thread <A> cannot release Mutex [ECMX] acquired by
thread <B> (20230628/exmutex-378)
kernel: ACPI: \_SB_.AC__: Error reading AC Adapter state: AE_AML_NOT_OWNER
Followed by hung EC event processing, then thermald/upowerd/kworker hangs, then
systemd PID 1 hang and total D-Bus service-activation failure.
## Regression range
- Good: 6.8.0-146 (and earlier: -139, -138, -137). Rare deadlocks (days apart).
- Bad: 6.8.0-147. Frequent deadlocks (multiple per day).
- -147 is stable patchset LP: #2168026.
## Suspected commits (not bisected)
1. PRIME: "ACPI: AC: Properly notify power management core about changes"
— hits the exact AC._PSR path that grabs [ECMX]; plausibly increases _PSR
evaluation frequency.
2. cpuidle menu governor cluster ("Remove iowait influence", "Select polling
state in some more cases", plus a mid-series revert) — alters CPU idle/wake
timing and hence EC poll frequency.
3. ACPICA lock/opregion changes (evxfregn ContextMutex, "Allow to skip Global
Lock initialization", acpi_ev_address_space_dispatch NULL-deref,
acpi_execute_reg_methods depth arg) — touch EC opregion/mutex machinery.
## Requested outcome
Given the root cause is HP firmware, a DMI-based quirk for this model (EliteBook
860 G10) that restores -146 AC-notify / idle behaviour, or a revert of the
offending change on affected hardware, would fix this for all affected users.
## Reproduction
Boot 6.8.0-147 on an affected machine and use normally; deadlock typically
occurs within minutes to a couple of hours. Does not occur (or very rarely)
on 6.8.0-146.
## Workaround in place
Pinned GRUB default to 6.8.0-146.
## Attachments (single archive: ecmx-bug-report.tar.gz)
Required by the kernel bug template:
- version.log (/proc/version_signature — note: shows -146, the GOOD
kernel, as that is what is currently booted; -147 is
the
bad one, see "Regression range" above)
- lspci-vnvn.log (sudo lspci -vnvn, full)
Supporting evidence:
- system-info.txt (model, BIOS, installed kernels, running kernel)
- cmdline.txt (/proc/cmdline)
- cpuinfo.txt (/proc/cpuinfo)
- dmesg-boot-minus5-full.txt (full kernel log from a deadlock boot)
- ecmx-logs-boot-minus5.txt (ECMX + AC._PSR + AE_AML_NOT_OWNER signatures)
- ecmx-logs-boot-minus8.txt (same, a second deadlock boot)
- acpi-tables/ (DSDT, SSDT1-29, FACP — raw ACPI tables containing the
_PSR/[ECMX] AML; verified free of serial number /
UUID)
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: acpi hp-elitebook noble regression-update
** Attachment added: "Archive of various files for system info and logs"
https://bugs.launchpad.net/bugs/2171947/+attachment/6011714/+files/ecmx-bug-report.tar.gz
** Tags added: acpi hp-elitebook noble regression-update
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https://bugs.launchpad.net/bugs/2171947
Title:
6.8.0-147 regression: massively increased frequency of ACPI [ECMX] EC-
mutex deadlock on HP EliteBook 860 G10 (AC._PSR), -146 unaffected
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