> The assumptions were that we would be dealing with two or more locks, with the
> same SPL, and that the acquire and release would be done locally. That's not
> general enough though. So, following your suggestion, something like this:
> 
> 	mutex_enter(a);
> 	.. find b ..
> 	mutex_enter(b);
>         mutex_link(b, mutex_exit_linked(a));
>         .. update b ..
>         mutex_exit(b);
> 
> This is a part of the design I'm not comfortable with, and I think the above
> is quite ugly. What do people think?

what's wrong with using plain old splxxx() where out-of-order operation is
really necessary?  i don't think it's often.

YAMAMOTO Takashi