Should fix PR/36939 and make the rlimit code MP safe.
Posted for comment to tech-kern (non received!)
The p_limit field (for a process) is only be changed once (on the first
write), and a reference to the old structure is kept (for code paths
that have cached the pointer).
Only p->p_limit is now locked by p->p_mutex, and since the referenced memory
will not go away, is only needed if the pointer is to be changed.
The contents of 'struct plimit' are all locked by pl_mutex, except that the
code doesn't bother to acquire it for reads (which are basically atomic).
Add FORK_SHARELIMIT that causes fork1() to share the limits between parent
and child, use it for the IRIX_PR_SULIMIT.
Fix borked test for both IRIX_PR_SUMASK and IRIX_PR_SDIR being set.
2e20a70dbf