A comment

proc.c

@@ -327,6 +327,9 @@ forkret(void)
   release(&ptable.lock);
 
   if (first) {
+    // Some initialization functions must be run in the context
+    // of a regular process (e.g., they call sleep), and thus cannot 
+    // be run from main().
     first = 0;
     initlog();
   }