I recently built a PC based on Intel's latest Skylake CPU (i5-6500) and Z170 chipset (AsRock Z170 Pro4), and installed Ubuntu 15.10 on it. After setting up, however, I found that the kernel message buffer was flooded with this error message. This is how I fixed it.

TL;DR

This is how to fix it: add this line to /etc/rc.local:

echo "disable" > /sys/firmware/acpi/interrupts/gpe6F

Then reboot your PC, the error message should be gone. If you want to learn more about how I came up with fix, keep reading.

The Symptoms

As described earlier, after the system booted up, this error message flooded the kernel ring buffer:

[    0.922778] ACPI Exception: AE_NOT_FOUND, while evaluating GPE method [_L6F] (20150619/evgpe-592)
[    0.923906] ACPI Error: [PGRT] Namespace lookup failure, AE_NOT_FOUND (20150619/psargs-359)
[    0.923908] ACPI Error: Method parse/execution failed [\_GPE._L6F] (Node ffff8804654cd118), AE_NOT_FOUND (20150619/psparse-536)

These three error messages were printed over and over again, and the /var/log/kern.log file rapidly exceeds several GB in about half an hour.

Attempts

After Googling around, I found this kernel bug report that is exactly the same problem:

https://bugzilla.kernel.org/show_bug.cgi?id=105491

It seems that adding acpi=off to kernel arguments could eliminate this error, but that will also disable all the ACPI functionality and the system would not be shut down properly (got stuck when do a sudo reboot).

I also updated to the latest BIOS (v2.80) from AsRock, that still does not fix the problem.

Finally, later on that thread, somebody mentioned that we could just disable the GPE.L6F function by echoing disable to a specific pseudo file in /sys directory, hence the solution mentioned earlier.