Refactor process_exit to add more comments for readability

src/userprog/process.c

@@ -209,7 +209,7 @@ process_init_stack (char *cmd_saveptr, void **esp, char *file_name)
         /* filename has already been validated to be a safe-to-access string,
            so we can safely use strlen here. Filename has already been
            split from the command line arguments. */
-        push_to_stack (esp, arg, strlen (arg) + 1);
+        push_to_stack (esp, arg, (strlen (arg) + 1) * sizeof (char));
 
         /* Try to allocate memory for the argument pointer. */
         struct arg_elem *arg_elem = malloc (sizeof (struct arg_elem));
@@ -376,9 +376,10 @@ process_exit (void)
   /* Clean up all open files */
   hash_destroy (&cur->open_files, fd_cleanup);
 
-  /* Close the executable file. */
+  /* Close the executable file, implicitly allowing it to be written to. */
   if (cur->exec_file != NULL)
     {
+      /* Acquire the file system lock to prevent race conditions. */
       lock_acquire (&filesys_lock);
       file_close (cur->exec_file);
       lock_release (&filesys_lock);