Protect the per-process UAC field with the proc lock where it isn't already

protected.

sys/alpha/alpha/vm_machdep.c

@@ -119,7 +119,9 @@ cpu_fork(td1, p2, td2, flags)
 	td2->td_pcb = (struct pcb *)
 	    (td2->td_kstack + KSTACK_PAGES * PAGE_SIZE) - 1;
 	td2->td_md.md_flags = td1->td_md.md_flags & MDTD_FPUSED;
+	PROC_LOCK(p2);
 	p2->p_md.md_uac = p1->p_md.md_uac;
+	PROC_UNLOCK(p2);
 
 	/*
 	 * Cache the physical address of the pcb, so we can

sys/alpha/include/proc.h

@@ -62,7 +62,7 @@ struct mdthread {
 #define	MDP_UAC_MASK	(MDP_UAC_NOPRINT | MDP_UAC_NOFIX | MDP_UAC_SIGBUS)
 
 struct mdproc {
-	u_int	md_uac;			/* Unaligned Access Check flags. */
+	u_int	md_uac;			/* (c) Unaligned Access Check flags. */
 };
 
 #endif /* !_MACHINE_PROC_H_ */