From 0084d12fb1924237b95fa0af3c87aab248877c80 Mon Sep 17 00:00:00 2001
From: Themis Demetriades <td1223@ic.ac.uk>
Date: Fri, 6 Dec 2024 17:30:46 +0000
Subject: [PATCH] fix: synchronise destruction of page directories with frame
 table

---
 src/userprog/pagedir.c |  3 +++
 src/vm/frame.c         | 11 +++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/userprog/pagedir.c b/src/userprog/pagedir.c
index 1d79b38..f12f0ce 100644
--- a/src/userprog/pagedir.c
+++ b/src/userprog/pagedir.c
@@ -6,6 +6,7 @@
 #include "threads/init.h"
 #include "threads/pte.h"
 #include "threads/palloc.h"
+#include "threads/synch.h"
 #include "vm/frame.h"
 #include "vm/page.h"
 
@@ -35,6 +36,7 @@ pagedir_destroy (uint32_t *pd)
     return;
 
   ASSERT (pd != init_page_dir);
+  lock_acquire (&lru_lock);
   for (pde = pd; pde < pd + pd_no (PHYS_BASE); pde++)
     if (*pde & PTE_P) 
       {
@@ -53,6 +55,7 @@ pagedir_destroy (uint32_t *pd)
         palloc_free_page (pt);
       }
   palloc_free_page (pd);
+  lock_release (&lru_lock);
 }
 
 /* Returns the address of the page table entry for virtual
diff --git a/src/vm/frame.c b/src/vm/frame.c
index c1d5ae3..a9028f1 100644
--- a/src/vm/frame.c
+++ b/src/vm/frame.c
@@ -209,8 +209,13 @@ frame_free (void *frame)
              "but this address is not allocated!\n",
              frame);
 
+    bool lock_held = lock_held_by_current_thread (&lru_lock);
+
     free_owners (&frame_metadata->owners);
-    lock_acquire (&lru_lock);
+
+    if (!lock_held)
+      lock_acquire (&lru_lock);
+
     hash_delete (&frame_table, &frame_metadata->hash_elem);
     list_remove (&frame_metadata->list_elem);
 
@@ -224,7 +229,9 @@ frame_free (void *frame)
         else
           next_victim = lru_next (next_victim);
       }
-    lock_release (&lru_lock);
+
+    if (!lock_held)
+      lock_release (&lru_lock);
 
     free (frame_metadata);
     palloc_free_page (frame);