[PATCH] MdeModulePkg PiSmmCore: Set ForwardLink to NULL in RemoveOldEntry()

[Star Zeng <star.zeng@intel.com>]

"Entry->Link.ForwardLink = NULL;" is present in RemoveMemoryMapEntry()
for DxeCore, that is correct.
"Entry->Link.ForwardLink = NULL;" is absent in RemoveOldEntry()
for PiSmmCore, that is incorrect.

Without this fix, when FromStack in Entry is TRUE,
the "InsertTailList (&mMapStack[mMapDepth].Link, &Entry->Link);" in
following calling to CoreFreeMemoryMapStack() will fail as the entry
at mMapStack[mMapDepth] actually has been removed from the list.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
---
 MdeModulePkg/Core/PiSmmCore/Page.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/MdeModulePkg/Core/PiSmmCore/Page.c b/MdeModulePkg/Core/PiSmmCore/Page.c
index 8909d46a00a2..3699af742458 100644
--- a/MdeModulePkg/Core/PiSmmCore/Page.c
+++ b/MdeModulePkg/Core/PiSmmCore/Page.c
@@ -1,7 +1,7 @@
 /** @file
   SMM Memory page management functions.
 
-  Copyright (c) 2009 - 2016, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2009 - 2018, Intel Corporation. All rights reserved.<BR>
   This program and the accompanying materials are licensed and made available
   under the terms and conditions of the BSD License which accompanies this
   distribution.  The full text of the license may be found at
@@ -246,6 +246,8 @@ RemoveOldEntry (
   )
 {
   RemoveEntryList (&Entry->Link);
+  Entry->Link.ForwardLink = NULL;
+
   if (!Entry->FromStack) {
     InsertTailList (&mFreeMemoryMapEntryList, &Entry->Link);
   }
-- 
2.7.0.windows.1