(trying again) how to get kernel stack trace if process not blocked?

[Ethan Wilson <ethan.wilson@shiftmail.org>]

Hello list,
I know cat /proc/pid/stack shows the kernel call stack of a process, and 
this is so good, but it will show just 0xffffffffffffffff if the process 
is running in kernel space and not blocked (sleeping).

It would be *very* useful to get the kernel stack trace for a running 
process, even if imprecise, or at least knowing the name of the kernel 
function executing now (top of the stack). Why is it not doable?

I tried to disable CONFIG_SCHED_OMIT_FRAME_POINTER but it didn't allow 
to print the stack from /proc/pid/stack anyway. What is the benefit of 
disabling such kernel option (i.e. having the frame pointer)?

I guessed that maybe with EIP from /proc/pid/stat it is possible to do 
something like that but I can't find much information on how to do that.

Thanks for any information
EW