After more experimentation, I find that the runaway ACPI process occurs every time I suspend/resume (Fn-backspace). (The system resumes fine apart from the runaway ACPI process.)
Is there any to kill or reset the kernel ACPI process short of rebooting? /ps/ doen't see it, and /pkill/ (even /pkill -9/) has no effect. I will try compiling a custom kernel with ACPITHINKPAD_DEBUG defined in /usr/src/sys/dev/acpi/acpithinkpad.c and see if that prints anything interesting. Are there any other particularly useful debugging things I should explore to help track down the problem? -- -- "Jonathan Thornburg [remove color- to reply]" <jthorn4...@pink-gmail.com> on the west coast of Canada, eh? "There was of course no way of knowing whether you were being watched at any given moment. How often, or on what system, the Thought Police plugged in on any individual wire was guesswork. It was even conceivable that they watched everybody all the time." -- George Orwell, "1984"