.

bigfile/tests/test_virtmem.c

@@ -1386,7 +1386,6 @@ void test_file_access_mmapoverlay(void)
     xmunmap(b0, PS);
     xmunmap(b2, PS);
 
-    // XXX verify notify_munmap was correctly called
 
     /* map vma back - dirty pages should be there _and_ mapped to vma.
      * (this differs from !wcfs case which does not mmap dirty pages until access) */

bigfile/virtmem.c

@@ -707,16 +707,43 @@ VMFaultResult vma_on_pagefault(VMA *vma, uintptr_t addr, int write)
     page = pagemap_get(&fileh->pagemap, pagen);
 
     /* wcfs: all dirty pages are mmapped when vma is created.
-     *       thus here, if page is present in pagemap, it can be only either
+     *       thus here, normally, if page is present in pagemap, it can be only either
      *       - a page we just loaded for dirtying, or
      *       - a page that is in progress of being loaded.
      *
+     *       however it can be also a *dirty* page due to simultaneous write
+     *       access from 2 threads:
+     *
+     *            T1                                   T2
+     *
+     *         write pagefault                      write pagefault
+     *         virt_lock
+     *         page.state = PAGE_LOADING
+     *         virt_unlock
+     *         # start loading the page
+     *         ...
+     *         # loading completed
+     *         virt_lock
+     *         page.state = PAGE_LOADED_FOR_WRITE
+     *         virt_unlock
+     *         return VM_RETRY
+     *                                              virt_lock
+     *                                              # sees page.state = PAGE_LOADED_FOR_WRITE
+     *                                              page.state = PAGE_DIRTY
+     *                                              virt_unlock
+     *
+     *         # retrying
+     *         virt_lock
+     *         # sees page.state = PAGE_DIRTY  <--
+     *
+     *
      * ( PAGE_LOADED_FOR_WRITE is used only to verify that in wcfs mode we
      *   always keep all dirty pages mmapped on fileh_open and so pagefault
      *   handler must not see a PAGE_LOADED page. )
      */
     if (fileh->mmap_overlay && page)
-        ASSERT(page->state == PAGE_LOADED_FOR_WRITE || page->state == PAGE_LOADING);
+        ASSERT(page->state == PAGE_LOADED_FOR_WRITE || page->state == PAGE_LOADING ||
+               page->state == PAGE_DIRTY);
 
     /* (4) no page found - allocate new from ram */
     while (!page) {