Clean up code in preparation for refactor

src/threads/thread.c

@@ -378,6 +378,7 @@ void thread_exit(void) {
 
         if (kid != NULL && kid->status == THREAD_DYING
             && kid != initial_thread) {
+            list_remove(&kid->kid_elem);
             palloc_free_page(kid);
         }
     }

src/userprog/process.c

@@ -153,11 +153,14 @@ int process_wait(tid_t child_tid UNUSED) {
     for (e = list_begin(&cur->kids); e != list_end(&cur->kids);
          e = list_next(e)) {
         kid = list_entry(e, struct thread, kid_elem);
+        lock_acquire(&kid->filesys_lock);
         if (kid->tid == child_tid && !kid->waited_on) {
             /* Next time we look for this kid, we return -1. */
             kid->waited_on = true;
+            lock_release(&kid->filesys_lock);
             break;
         }
+        lock_release(&kid->filesys_lock);
     }
 
     /* Check if no kid with child_tid. */
@@ -168,9 +171,6 @@ int process_wait(tid_t child_tid UNUSED) {
     /* Wait for child thread to die. */
     sema_down(&kid->wait_sema);
 
-    /* Thread exit should have already been called. */
-    ASSERT(kid->status == THREAD_DYING);
-
     /* If child thread is done, just get exit status. */
     int child_exit_status = kid->exit_status;
     kid->parent = NULL;
@@ -187,6 +187,11 @@ void process_exit(void) {
     struct thread *cur = thread_current();
     uint32_t *pd;
 
+    /* Free executable */
+    if (cur->executable != NULL) {
+        file_allow_write(cur->executable);
+    }
+
     /* Destroy the current process's page directory and switch back
        to the kernel-only page directory. */
     pd = cur->pagedir;

src/userprog/syscall.c

@@ -177,30 +177,14 @@ void sys_halt(void) {
 void sys_exit(int status) {
     struct thread *cur = thread_current();
     printf("%s: exit(%d)\n", cur->name, status);
-
     cur->exit_status = status;
 
-    if (lock_held_by_current_thread(&filesys_lock)) {
-        release_file_lock();
-    }
-
-    /* Free executable */
-    if (cur->executable != NULL) {
-        file_allow_write(cur->executable);
-    }
-
     /* Free all file buffers. */
     struct list_elem *e;
-    for (e = list_begin(&cur->open_files);
-         e != list_end(&cur->open_files);
-         /* increment in loop */) {
+    while (!list_empty(&cur->open_files)) {
+        e = list_begin(&cur->open_files);
         struct sys_file *open_file =
             list_entry(e, struct sys_file, file_elem);
-
-        /* Increment before removing. */
-        e = list_next(e);
-
-        /* File system call */
         sys_close(open_file->fd);
     }
     thread_exit();