From 9cc8dabd47161cc63cb9738bb70e6019dc68fbd0 Mon Sep 17 00:00:00 2001
From: Hang Park <hangpark@kaist.ac.kr>
Date: Sun, 21 May 2017 17:27:24 +0900
Subject: [PATCH] [#138] Avoid race b/w frame table and swap table

---
 src/vm/frame.c | 11 ++++++++---
 src/vm/swap.c  | 34 +++++++++++++++++++++++++++++++---
 2 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/src/vm/frame.c b/src/vm/frame.c
index 005f12d..831cd5f 100644
--- a/src/vm/frame.c
+++ b/src/vm/frame.c
@@ -14,14 +14,14 @@
 #include "vm/swap.h"
 
 /* Frame table lock. */
-struct lock frame_table_lock;
+static struct lock frame_table_lock;
 
 /* Frame table. */
-struct list frame_table;
+static struct list frame_table;
 
 #ifdef VM_CLOCK
 /* Current frame table position. */
-struct list_elem *frame_table_pos;
+static struct list_elem *frame_table_pos;
 #endif
 
 /* Frame table element. */
@@ -216,6 +216,7 @@ static struct frame *
 frame_next_circ (void)
 {
   ASSERT (!list_empty (&frame_table));
+  ASSERT (lock_held_by_current_thread (&frame_table_lock));
 
   struct list_elem *next;
   if (frame_table_pos == list_back (&frame_table)
@@ -233,6 +234,8 @@ frame_next_circ (void)
 static struct frame *
 frame_to_evict_clock (void)
 {
+  ASSERT (lock_held_by_current_thread (&frame_table_lock));
+
   struct frame *f;
   for (f = frame_next_circ ();
        pagedir_is_accessed (f->suppl_pte->pagedir, f->suppl_pte->upage);
@@ -248,6 +251,8 @@ frame_to_evict_clock (void)
 static struct frame *
 frame_to_evict_fifo (void)
 {
+  ASSERT (lock_held_by_current_thread (&frame_table_lock));
+
   struct frame *f = list_entry (list_begin (&frame_table), struct frame, elem);
   list_remove (&f->elem);
   list_push_back (&frame_table, &f->elem);
diff --git a/src/vm/swap.c b/src/vm/swap.c
index d519523..086909a 100644
--- a/src/vm/swap.c
+++ b/src/vm/swap.c
@@ -1,18 +1,27 @@
 #include <bitmap.h>
 #include <debug.h>
 #include "devices/disk.h"
+#include "threads/synch.h"
 #include "threads/vaddr.h"
 #include "vm/swap.h"
 
 #define SECTORS_PER_PAGE (PGSIZE / DISK_SECTOR_SIZE)
 
+/* Swap table lock. */
+static struct lock swap_table_lock;
+
+/* Swap disk. */
 static struct disk *swap_disk;
+
+/* Swap table. */
 static struct bitmap *swap_table;
 
 /* Initializes the swap table. */
 void
 swap_table_init (void)
 {
+  lock_init (&swap_table_lock);
+
   /* Get swap disk. */
   swap_disk = disk_get (1, 1);
   if (swap_disk == NULL)
@@ -38,13 +47,21 @@ swap_table_init (void)
 bool
 swap_in (void *kpage, size_t idx)
 {
+  lock_acquire (&swap_table_lock);
+
   /* False if index is larger than swap table size. */
   if (idx >= bitmap_size (swap_table))
-    return false;
+    {
+      lock_release (&swap_table_lock);
+      return false;
+    }
 
   /* False if swap slot is empty. */
   if (bitmap_test (swap_table, idx))
-    return false;
+    {
+      lock_release (&swap_table_lock);
+      return false;
+    }
 
   /* Copy contents from swap disk to frame. */
   disk_sector_t sec_no = SECTORS_PER_PAGE * idx;
@@ -59,6 +76,8 @@ swap_in (void *kpage, size_t idx)
   /* Set swap slot empty. */
   bitmap_set (swap_table, idx, true);
 
+  lock_release (&swap_table_lock);
+
   return true;
 }
 
@@ -68,10 +87,15 @@ swap_in (void *kpage, size_t idx)
 size_t
 swap_out (void *kpage)
 {
+  lock_acquire (&swap_table_lock);
+
   /* Get empty swap slot. */
   size_t idx = bitmap_scan (swap_table, 0, 1, true);
   if (idx == BITMAP_ERROR)
-    return BITMAP_ERROR;
+    {
+      lock_release (&swap_table_lock);
+      return BITMAP_ERROR;
+    }
 
   /* Copy contents from frame to swap disk. */
   disk_sector_t sec_no = SECTORS_PER_PAGE * idx;
@@ -86,6 +110,8 @@ swap_out (void *kpage)
   /* Set swap slot not empty. */
   bitmap_set (swap_table, idx, false);
 
+  lock_release (&swap_table_lock);
+
   return idx;
 }
 
@@ -93,5 +119,7 @@ swap_out (void *kpage)
 void
 swap_remove (size_t idx)
 {
+  lock_acquire (&swap_table_lock);
   bitmap_set (swap_table, idx, true);
+  lock_release (&swap_table_lock);
 }