Fix child_results loop accessing after free()

src/userprog/process.c

@@ -47,6 +47,9 @@ struct process_start_data
                           tokens while maintaining state. */
     char file_name[FNAME_MAX_LEN + 1]; /* Name of the file of the process to
                                       be started. */
+    struct semaphore load_sema;
+
+    bool success;
   };
 
 static thread_func start_process NO_RETURN;
@@ -62,11 +65,7 @@ process_execute (const char *cmd)
   char *cmd_copy;
   tid_t tid;
   
-  struct process_start_data *data = malloc (sizeof (struct process_start_data));
-  if (data == NULL)
-    {
-      return TID_ERROR;
-    }
+  struct process_start_data data;
 
   /* Make a copy of command.
      Otherwise there's a race between the caller and load(). */
@@ -80,7 +79,7 @@ process_execute (const char *cmd)
 
   /* Retrieve first argument of command, which is the file name
      of the process. */
-  char *file_name = strtok_r (cmd_copy, " ", &data->cmd_saveptr);
+  char *file_name = strtok_r (cmd_copy, " ", &data.cmd_saveptr);
 
   /* NOTE: Currently, the file being executed is closed in load () and then
           reopened here. Because load is an exported public function, this
@@ -95,12 +94,24 @@ process_execute (const char *cmd)
   /* Create a new thread to execute the command, by initializing
      it running the function 'start_process' with the appropriate
      arguments. For details of arguments, see 'start_process'. */
-  data->cmd = cmd_copy;
-  strlcpy (data->file_name, file_name, FNAME_MAX_LEN + 1);
+  data.cmd = cmd_copy;
+  strlcpy (data.file_name, file_name, FNAME_MAX_LEN + 1);
+  sema_init (&data.load_sema, 0);
+  data.success = false;
+
+  tid = thread_create (file_name, PRI_DEFAULT, start_process, &data);
 
-  tid = thread_create (file_name, PRI_DEFAULT, start_process, data);
   if (tid == TID_ERROR)
-    palloc_free_page (cmd_copy); 
+    {
+      palloc_free_page (cmd_copy);
+    }
+  else
+    {
+      sema_down (&data.load_sema);
+      if (!data.success)
+        tid = TID_ERROR;
+    }
+
   return tid;
 }
 
@@ -118,7 +129,6 @@ static void
 start_process (void *proc_start_data)
 {
   struct intr_frame if_;
-  bool success;
 
   struct process_start_data *data = proc_start_data;
 
@@ -136,21 +146,22 @@ start_process (void *proc_start_data)
   file_deny_write (exec_file);
   lock_release (&filesys_lock);
 
-  success = load (data->file_name, &if_.eip, &if_.esp);
+  data->success = load (data->file_name, &if_.eip, &if_.esp);
 
   /* If load failed, free process startup data and quit. */
-  if (!success) 
+  if (!data->success)
     {
       palloc_free_page (data->cmd);
-      free (data);
+      sema_up (&data->load_sema);
       thread_exit ();
     }
 
   /* Initialize user process stack and free page used to store the
      command that executed the process. */
-  success = process_init_stack (data->cmd_saveptr, &if_.esp, data->file_name);
+  bool success = process_init_stack (data->cmd_saveptr, &if_.esp, data->file_name);
   palloc_free_page (data->cmd);
-  free (data);
+  data->success = success;
+  sema_up (&data->load_sema);
   
   /* If stack initialization failed, free process resources and quit. */
   if (!success)
@@ -297,7 +308,6 @@ process_wait (tid_t child_tid UNUSED)
     }
   if (child_result == NULL)
     {
-      printf ("-1 due to: child_result == NULL\n");
       return -1;
     }
   /* Wait for child to die. */
@@ -314,11 +324,6 @@ process_wait (tid_t child_tid UNUSED)
   lock_release (&child_result->lock);
   free (child_result);
 
-  if (exit_status == -1)
-    {
-      printf ("-1 due to: child exit status wrong!\n");
-    }
-
   return exit_status;
 }
 
@@ -327,16 +332,15 @@ void
 process_exit (void)
 {
 
-  printf("(%d) EXIT STATUS: %d\n", thread_current ()->tid, thread_current ()->exit_status);
 
   struct thread *cur = thread_current ();
   uint32_t *pd;
 
   printf ("%s: exit(%d)\n", cur->name, cur->exit_status);
+
   if (cur->exec_file != NULL)
     {
       lock_acquire (&filesys_lock);
-      file_allow_write (cur->exec_file);
       file_close (cur->exec_file);
       lock_release (&filesys_lock);
     }
@@ -364,10 +368,11 @@ process_exit (void)
   /* Free child process results or signal parent's death. */
   struct list_elem *e;
   for (e = list_begin (&cur->child_results);
-       e != list_end (&cur->child_results); e = list_next (e))
+       e != list_end (&cur->child_results);)
     {
       struct process_result *result
           = list_entry (e, struct process_result, elem);
+      struct list_elem *next = list_next (e);
       lock_acquire (&result->lock);
       /* Child has died (and was not waited for). Free the result. */
       if (sema_try_down (&result->sema))
@@ -381,6 +386,7 @@ process_exit (void)
           sema_up (&result->sema);
           lock_release (&result->lock);
         }
+      e = next;
     }
 
   /* Destroy the current process's page directory and switch back