Signal delivery

[Unix learner]

Hi Guys,
     Need to clarify some concepts about signaling mechanism in linux kernel 2.4 and 2.6 ?

What time the signal to a process is really delivered --
1. After moving from kernel space to user space - yes
2. After the process in kernel space wakes up from interruptible/uninterruptible sleep -- ??
3. Can a kernel thread be signaled ? What time does it check for its pending signals ?
4. Can a user process signal a kernel thread (visible through ps), or only another kernel process can do that ? How is it implemented ?


Thanks!