[im]proper use of stack?

[mfbaustx <mfbaustx@gmail.com>]

So... I know that there is some small-ish amount of kernel stack space  
available per-process, and the kernel uses this area when executing on a  
process's behalf (system call, etc).  Let's say I allocate (via an  
automatic/stack-based storage) some smallish structure which I want a  
kernel thread to populate (or interrupt context... some context other than  
my process's context).

If my process gets context swapped, is my kernel-based stack pointer  
always valid?

Why use stack-based storage, you ask?  Let's pretend this is a  
high-frequency call and I don't want to incur the expense of kmalloc'ing  
and freeing on every call.  I know I have enough stack space, I just don't  
know if my stack is always available  :)

TIA!