A question about in lock usage in FreeBSD

[Jia-Ju Bai]

Hi,

I am a freshman in developing FreeBSD drivers, and I have a question in 
lock usage in FreeBSD.

The kernel provides some kinds of locks in developing drivers, such as 
"mutex lock", "mutex spin lock", "rw lock" and "sx lock". I want to know 
which locks should be held when the thread can sleep.
 From my knowledge of FreeBSD document, I make the following points:
(1) "rw lock" and "sx lock" can be used in this situation;
(2) "mutex lock" and "mutex spin lock" are forbidden in this situation.

If my points are right, I will make another point:
mutex_lock will let the thread sleep when the lock is requested, so the 
mutex_lock can not be called in nested style (namely it is unsafe that 
mutex_lock is called again when a "mutex lock" is held).

Are my points are right?
I am looking forward to useful opinions and answers :)

Thanks in advance :)
Jia-Ju Bai