From 46fa9ae1f477c7a6ec161efa7d8314611eddf37a Mon Sep 17 00:00:00 2001
From: Paul Durrant <paul.durrant@citrix.com>
Date: Fri, 31 Jan 2014 17:44:53 +0000
Subject: [PATCH] Add a magic number to the frontend structure that can be
 checked for in the mib callback. There's a suspicion that the callback may be
 occuring after xenvif has unloaded.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
---
 src/xenvif/frontend.c | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/src/xenvif/frontend.c b/src/xenvif/frontend.c
index 6b1e6e4..33c8f69 100644
--- a/src/xenvif/frontend.c
+++ b/src/xenvif/frontend.c
@@ -55,6 +55,7 @@
 #include "assert.h"
 
 struct _XENVIF_FRONTEND {
+    ULONG                       Magic;
     PXENVIF_PDO                 Pdo;
     PCHAR                       Path;
     PCHAR                       Prefix;
@@ -80,6 +81,8 @@ struct _XENVIF_FRONTEND {
     HANDLE                      Handle;
 };
 
+#define FRONTEND_MAGIC  0xf00ba4ed
+
 static const PCHAR
 FrontendStateName(
     IN  XENVIF_FRONTEND_STATE   State
@@ -663,6 +666,8 @@ FrontendIpAddressChange(
     UNREFERENCED_PARAMETER(_Row);
     UNREFERENCED_PARAMETER(NotificationType);
 
+    ASSERT3U(Frontend->Magic, ==, FRONTEND_MAGIC);
+
     ThreadWake(Frontend->MibThread);
 }
 
@@ -1555,6 +1560,8 @@ FrontendInitialize(
 
     Trace("====>\n");
 
+    ASSERT3U(KeGetCurrentIrql(), ==, PASSIVE_LEVEL);
+
     Name = PdoGetName(Pdo);
 
     Length = sizeof ("devices/vif/") + (ULONG)strlen(Name);
@@ -1624,6 +1631,9 @@ FrontendInitialize(
     if (!NT_SUCCESS(status))
         goto fail11;
 
+    (*Frontend)->Magic = FRONTEND_MAGIC;
+    _ReadWriteBarrier();
+
     status = NotifyUnicastIpAddressChange(AF_UNSPEC,
                                           FrontendIpAddressChange,
                                           *Frontend,
@@ -1636,7 +1646,12 @@ FrontendInitialize(
         // If IP Helper isn't available (as in Windows PE) then
         // NotifyUnicastIpAddressChange will not be supported
         Warning("Cannot record or update network info to XAPI %x\n", status);
-        (*Frontend)->Handle = NULL;
+        // The documentation states that in the error case, the handle is
+        // always populated with NULL.
+        ASSERT((*Frontend)->Handle == NULL);
+    } else {
+        // By inference the handle should not be NULL in the success case
+        ASSERT((*Frontend)->Handle != NULL);
     }
 
     Trace("<====\n");
@@ -1646,6 +1661,8 @@ FrontendInitialize(
 fail12:
     Error("fail12\n");
 
+    (*Frontend)->Magic = 0;
+
     ThreadAlert((*Frontend)->MibThread);
     ThreadJoin((*Frontend)->MibThread);
     (*Frontend)->MibThread = NULL;
@@ -1726,14 +1743,23 @@ FrontendTeardown(
 {
     Trace("====>\n");
 
+    ASSERT3U(KeGetCurrentIrql(), ==, PASSIVE_LEVEL);
+
     ASSERT(Frontend->State != FRONTEND_ENABLED);
     ASSERT(Frontend->State != FRONTEND_CONNECTED);
 
     if (Frontend->Handle != NULL) {
-        CancelMibChangeNotify2(Frontend->Handle);
+        NTSTATUS    status;
+
+        status = CancelMibChangeNotify2(Frontend->Handle);
+        ASSERT(NT_SUCCESS(status));
+
         Frontend->Handle = NULL;
     }
 
+    _ReadWriteBarrier();
+    Frontend->Magic = 0;
+
     if (Frontend->State == FRONTEND_PREPARED) {
 
         ASSERT(Frontend->Watch != NULL);
-- 
2.39.5