fix: synchronise threads' SPTs with locks

src/threads/thread.c

@@ -736,6 +736,8 @@ init_thread (struct thread *t, const char *name, int nice, int priority,
   t->recent_cpu = recent_cpu;
   t->priority = t->base_priority;
 
+  lock_init (&t->pages_lock);
+
   old_level = intr_disable ();
   list_push_back (&all_list, &t->allelem);
   intr_set_level (old_level);

src/threads/thread.h

@@ -136,6 +136,7 @@ struct thread
     struct list_elem elem;              /* List element. */
 
     struct hash pages;                  /* Table of open user pages. */
+    struct lock pages_lock; /* Lock for the supplementary page table. */
 
     /* Memory mapped files for user virtual memory. */
     struct hash mmap_files;             /* List of memory mapped files. */