From 833c1b0520f0e85d16f32d8f65f73a0df2d677d4 Mon Sep 17 00:00:00 2001
From: Gleb Koval <gleb@koval.net>
Date: Thu, 5 Dec 2024 22:37:14 +0000
Subject: [PATCH] fix: only swap out shared pages once

---
 src/vm/page.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/src/vm/page.c b/src/vm/page.c
index 1a68430..b617994 100644
--- a/src/vm/page.c
+++ b/src/vm/page.c
@@ -71,17 +71,19 @@ static void page_set_swap (struct thread *owner, uint32_t *pte,
 bool
 page_insert_swapped (void *upage, void *kpage, struct list *owners)
 {
+  struct file *exec_file = NULL;
   struct list_elem *e;
   for (e = list_begin (owners); e != list_end (owners); e = list_next (e))
     {
       struct thread *owner = list_entry (e, struct frame_owner, elem)->owner;
       uint32_t *pte = lookup_page (owner->pagedir, upage, false);
-      if (page_is_shared_pte (pte))
+      if (exec_file != NULL || page_is_shared_pte (pte))
         {
-          ASSERT (list_size (owners) == 1);
+          ASSERT (page_is_shared_pte (pte));
           pagedir_clear_page (owner->pagedir, upage);
-          size_t swap_slot = swap_out (kpage);
-          return true;
+          exec_file = owner->exec_file;
+          ASSERT (exec_file != NULL);
+          continue;
         }
       ASSERT (list_size (owners) == 1);
 
@@ -112,6 +114,14 @@ page_insert_swapped (void *upage, void *kpage, struct list *owners)
 
       lock_release (&page->lock);
     }
+  if (exec_file != NULL)
+    {
+      lock_acquire (&shared_file_pages_lock);
+      struct shared_file_page *sfp = shared_file_page_get (exec_file, upage);
+      sfp->frame = NULL;
+      sfp->swap_slot = swap_out (kpage);
+      lock_release (&shared_file_pages_lock);
+    }
   return true;
 }