[ros-diffs] [sir_richard] 47148: [NTOS]: At times, pages may be removed from the zero or free page list, but without being initialized as part of the PFN database, such that their PageLocation has not changed. However, we can detect these pages because their link pointers will be NULL, meaning they're not _really_ free or zeroed. Use this enhanced check when verifying if a page is in use or not, and additionally triple-check by making sure the reference count is zero. This now matches the Windows checks. We also consider Standby pages (not yet implemented) as usable, since we can always steal them.

[sir_richard at svn.reactos.org]

Author: sir_richard
Date: Sun May  9 20:06:38 2010
New Revision: 47148

URL: http://svn.reactos.org/svn/reactos?rev=47148&view=rev
Log:
[NTOS]: At times, pages may be removed from the zero or free page list, but without being initialized as part of the PFN database, such that their PageLocation has not changed. However, we can detect these pages because their link pointers will be NULL, meaning they're not _really_ free or zeroed. Use this enhanced check when verifying if a page is in use or not, and additionally triple-check by making sure the reference count is zero. This now matches the Windows checks. We also consider Standby pages (not yet implemented) as usable, since we can always steal them.

Modified:
    trunk/reactos/ntoskrnl/mm/freelist.c

Modified: trunk/reactos/ntoskrnl/mm/freelist.c
URL: http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/mm/freelist.c?rev=47148&r1=47147&r2=47148&view=diff
==============================================================================
--- trunk/reactos/ntoskrnl/mm/freelist.c [iso-8859-1] (original)
+++ trunk/reactos/ntoskrnl/mm/freelist.c [iso-8859-1] Sun May  9 20:06:38 2010
@@ -130,10 +130,21 @@
 
 BOOLEAN
 NTAPI
+MiIsPfnFree(IN PMMPFN Pfn1)
+{
+    /* Must be a free or zero page, with no references, linked */
+    return ((Pfn1->u3.e1.PageLocation <= StandbyPageList) &&
+            (Pfn1->u1.Flink) &&
+            (Pfn1->u2.Blink) &&
+            !(Pfn1->u3.e2.ReferenceCount));
+}
+
+BOOLEAN
+NTAPI
 MiIsPfnInUse(IN PMMPFN Pfn1)
 {
-    return ((Pfn1->u3.e1.PageLocation != FreePageList) &&
-            (Pfn1->u3.e1.PageLocation != ZeroedPageList));
+    /* Standby list or higher, unlinked, and with references */
+    return !MiIsPfnFree(Pfn1);
 }
 
 PFN_NUMBER