Signal handling for linux kernel thread (jffs2 garbage collection thread to be specific)

Question

I am trying to manually trigger jffs2 garbage collection thread by sending it SIGHUP with kill -s SIGHUP

(the source for the thread is here: http://lxr.linux.no/linux-old+*/fs/jffs2/background.c#L98)

I added a bunch of printk statement in the thread to tell me that the thread has run but none of the print statements got triggered. Even when I kill the thread by 'kill -9 ' I still didn't get a printk.

My questions are:

1) Is it correct to say that this jffs2 gc thread a kernel thread?

2) Does kernel thread handle signaling differently (when compared to user thread)?

3) In general, what are the differences between user process/thread and kernel process/thread (other than memory space access)?