[parisc-linux] ldcw in __pthread_acquire

[Alan Cox]

> we can use for semaphoring (msem_lock comes to mind...), which the lib
> (in arch specific code) either implements in a mixture of user/kernel
> space, or (if you can get to kernel mode cheaply), does it in kernel mode
> via a lightweight system call.
> 
> Note also that spinning in a ldcw is very painful for the bus, and
> switching to a ldw-loop followed by ldcw results in starvation in a
> greater-than-2-way MP system.

That sounds a good reason to do at least most of it in kernel space on hppa