Fix proc_kill () race, improve scheduler locking

kernel/proc/proc.h

@@ -11,6 +11,12 @@
 #include <amd64/proc.h> /* USTACK_SIZE */
 #endif
 
+/// Process is ready to run
+#define PROC_READY  0
+/// Process marked garbage collection
+#define PROC_DEAD   1
+
+
 struct cpu;
 
 struct proc_mapping {
@@ -30,6 +36,7 @@ struct proc {
   spin_lock_t lock;
   struct cpu* cpu;
   struct procw* procw; /* link to it's global struct */
+  atomic_int state;
 };
 
 /*