After dozens and dozens of boots with the 3.2.0-14 and 3.2.0-15 kernels, here’s what I know.

1. This *is* tied to wistron_btns as I reported. Without it, boot never fails (the way I initially reported, though I’ll redefine what ”fails” means further below).
2. With non-pae kernels, boot never fails.
3. With 3.2.0-14-pae, the boot always fails.
4. A cold boot with 3.2.0-15-pae never fails.
5. A re-boot with 3.2.0-15-pae after a *non-failing* boot never fails.
6. A re-boot of 3.2.0-15-pae, after a *failing* boot (of 3.2.0-14-pae for instance), is *almost* sure to fail. I’d give it a 10% chance of not failing.

If you put it another way, this appears is pretty interesting:
1. You can ”break” 3.2.0-15-pae by booting 3.2.0-14-pae first.
2. You ”fix” a thus ”broken” 3.2.0-15-pae by booting a non-pae kernel.

I suspect this brokenness is actually hidden in the hardware, in something (the wifi key perhaps?) controlled by wistron_btns. Booting 3.2.0-14-pae puts the controller(?) in a ”broken” state from which 3.2.0-15-pae can’t recover, but a non-pae kernel can. And though 3.2.0-15-pae can’t recover a ”broken” controller, it also cannot put it into that ”broken” state (which is a good turn of development).

So now, about that ”fails” part.

I discovered by accident that although the system appears to freeze in boots I referred to as ”fails”, it has in fact been brought down to *almost* complete halt, but *just* almost. If I’m patient enough to wait, it does actually boot into LDM, from where I can switch to another VT and log in… slooooooowly.

Thus I was able to find out what’s going on that makes it so slow:

jani@amilo:~$ head dmesg.fail
stron_btns: Unknown key code 10
[ 1011.554522] wistron_btns: Unknown key code 10
[ 1011.554722] wistron_btns: Unknown key code 10
[ 1011.554921] wistron_btns: Unknown key code 10
[ 1011.555120] wistron_btns: Unknown key code 10
[ 1011.555320] wistron_btns: Unknown key code 10
[ 1011.555518] wistron_btns: Unknown key code 10
[ 1011.555717] wistron_btns: Unknown key code 10
[ 1011.555916] wistron_btns: Unknown key code 10
[ 1011.556134] wistron_btns: Unknown key code 10
jani@amilo:~$ grep wistron dmesg.fail | wc -l
2520

Note that this is unrelated to pressing any actual physical buttons. It’ wistron_btns misbehaving under the conditions I described above.