My summary’s crap because this is difficult to summarize, hopefully the explanation below makes it clearer. I have little understanding of kernel internals, so I’ll first just try and describe the symptom as it appears.<\/p>\n
I’ve come across an issue on my Fujitsu Siemens Amilo M7400 laptop with wistron_btns that is triggered by certain kernels, and once triggered, seems to affect all subsequent attempts to reboot with -pae kernels until a non-pae kernel is booted. I initially reported this on Launchpad [1].<\/p>\n
I can currently trigger the issue by (cold or re-) booting 3.2.0-14-pae (these are Ubuntu’s packaged kernels) or by booting (for example) 3.3.0-030300rc4-generic-pae in recovery mode (= ”ro recovery nomodeset”). The recovery boot seems to work normally, but the 3.2.0-14-pae boot already exhibits the failure: it seemingly freezes. (More about the exact nature of ”failure” below.)<\/p>\n
Once I’ve triggered the issue, rebooting with any -pae kernel fails similar to how 3.2.0-14-pae behaves irregardless of preceding boots.<\/p>\n
I can ”fix” this by booting a non-pae kernel (which never fails). After that subsequent reboots with -pae kernels (apart from 3.2.0-14-pae) no longer fail \u2014 not until I do any of the triggering actions again.<\/p>\n
Now, the ”failure” looks like a freeze, but it’s actually just an extreme slowdown. With patience, I can actually have the boot finish and can inspect logs. Dmesg reveals that wistron_btns is repeating ”Unknown key code 10” over and over.<\/p>\n
If I comment wistron_btns out of \/etc\/modules so that it isn’t loaded, the issue goes away, meaning I can no longer trigger it.<\/p>\n
As I said, I have little understanding of kernel bugs, so what I say next may be completely off, but the way I’ve interpreted this is that the ”brokenness” is actually hidden in the hardware, in something controlled by wistron_btns. Booting 3.2.0-14-pae\/recovery booting any -pay puts the controller(?) in a ”broken” state from which a -pae kernel can’t recover, but a non-pae kernel can. And although -pae kernels later than 3.2.0-14 can’t recover a ”broken” controller, they also cannot put it into that ”broken” state (which is a good turn of development).<\/p>\n
I’ll be happy to provide more info as requested. I’m attaching dmesg output for
\nstarters.<\/p>\n