fix: do not leak when inserting the same page twice, just update

src/userprog/exception.c

@@ -292,7 +292,7 @@ fetch_page (void *upage, bool write)
   switch (page->type) {
     case PAGE_MMAP:
     case PAGE_FILE:
-      success = page_load_file (page, page->writable);
+      success = page_load_file (page);
       if (success && page->type == PAGE_FILE)
         {
           hash_delete (&thread_current ()->pages, &page->elem);

src/vm/page.c

@@ -95,6 +95,16 @@ page_insert_file (struct file *file, off_t ofs, void *upage,
                   uint32_t read_bytes, uint32_t zero_bytes, bool writable,
                   enum page_type type)
 {
+  /* If page exists, just update it. */
+  struct page_entry *existing = page_get (upage);
+  if (existing != NULL)
+    {
+      ASSERT (existing->read_bytes == read_bytes);
+      ASSERT (existing->zero_bytes == zero_bytes);
+      existing->writable = existing->writable || writable;
+      return existing;
+    }
+
   struct page_entry *page = malloc(sizeof (struct page_entry));
   if (page == NULL)
     return NULL;

src/vm/page.h

@@ -30,16 +30,14 @@ struct page_entry {
   struct hash_elem elem; /* An elem for the hash table. */
 };
 
-unsigned page_hash (const struct hash_elem *e, void *aux);
+bool init_pages (struct hash *pages);
-bool page_less (const struct hash_elem *a_, const struct hash_elem *b_,
-                void *aux);
 struct page_entry *page_insert_swapped (void *upage, void* kpage,
                                         struct thread *owner);
 struct page_entry *page_insert_file (struct file *file, off_t ofs, void *upage,
                                      uint32_t read_bytes, uint32_t zero_bytes,
                                      bool writable, enum page_type);
 struct page_entry *page_get (void *upage);
-bool page_load_file (struct page_entry *page, bool writable);
+bool page_load_file (struct page_entry *page);
 void page_cleanup (struct hash_elem *e, void *aux);
 
 bool page_in_swap (struct thread *, void *);