[2.6.39-rc[12]] hangs during boot

[Michael Guntsche <mike@it-loops.com>]

Good morning list,

I just tried 2.7.39-rc2 and then rc1 on one of my systems.  2.6.38 runs
without an issue on this hardware but with 2.6.39-rc[12] the system
crawls to a halt during the boot process. I manages to reach the end of
runlevel S but then it grinds to a halt. Waiting long enough I get a
hung task warning sooner or later. If I then hit a SYSRQ combo for
blocked tasks (which is empty btw) it seems to continue a little bit but
awfully slow. 
The problem with debugging this right now is twofold.
First of all, for some odd reason I do not get output on the serial
console during boot (to capture the SYSRQ info), second this is running
on a software RAID-5 so every forced reboot out of this state results in
a complete resync of the whole array.

I know this could be everything, IRQ, block layer problem etc, so maybe
someone has an idea how I can figure out, what's going on exactly apart
from bisecting between 38 and 39-rc1

On a side note since I read similar reports already. This is a happening
with a CONFIG_NO_HZ/TICK_ONESHOT non-PREEMPT kernel.

Kind regards,
Michael Guntsche