kern/38719: arm, m68k, vax have no cpu_info::ci_curlwp

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>Number:         38719
>Category:       kern
>Synopsis:       arm, m68k, vax have no cpu_info::ci_curlwp
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed May 21 08:10:00 +0000 2008
>Originator:     Andrew Doran
>Release:        4.99.63
>Organization:
The NetBSD Project
>Environment:
n/a
>Description:
Problem 1:

Most MI code is insensitive to preemption and MULTIPROCESSOR.
There are a few slowpath cases that inspect cpu_info::ci_curlwp.
These are among the last uses of #ifdef MULTIPROCESSOR in the MI
kernel.

We can't get rid of those ifdefs because on arm and vax ci_curlwp
is conditional, and the m68k ports still use a global variable.

Problem 2:

Where ci_curlwp is conditional, the MULTIPROCESSOR option breaks
ABI compatibility for kernel modules that play with low level
kernel stuff.

>How-To-Repeat:
Code inspection.
>Fix:
Make ci_curlwp mandatory.