Comment 11 for bug 1482273

I have tested the attached patch against ubuntu kernels 3.13.0-58, 3.13.0-63, 3.13.0-64, and 3.13.0-65 for over a month. Never once has this laptop suffered a kernel panic with the applied patch to reinstate the optimization to stepwise.c. It has never failed to boot. As I said earlier, I found the origin of the regression through a git bisect.

I also have tested the latest upstream kernel, version 4.3.0-040300rc3-generic #201509271225. It has no issue booting. Looking at:

https://github.com/torvalds/linux/blob/master/drivers/thermal/step_wise.c

I see that the commit which introduces this issue has not been applied upstream. Probably because commit 178c2490b99f898efc06d1ad75cadc84f13021a6 (thermal: step_wise: Revert optimization) is not needed due to 8c8dd64345ba2a8c41556095c7adacb1c8af7c1 ("acerhdf: Use bang-bang thermal governor") fixing the issue for the fan control upstream. So the issue I'm experiencing is not so much fixed upstream, as rather it never existed upstream.

I do have an old Acer Aspire 1410 which uses the acerhdf fan control module if you would like assistance in testing a backport of 8c8dd64345ba2a8c41556095c7adacb1c8af7c1 ("acerhdf: Use bang-bang thermal governor") to 3.13.0.

Ubuntu kernel 3.13.0-65-generic is still unable to reliably boot without a kernel panic.

Thanks