Fix token memory ordering issue reading from the MethodDef and FieldDef token tables

src/coreclr/vm/ceeload.cpp

@@ -4644,13 +4644,6 @@ void Module::EnumMemoryRegions(CLRDataEnumMemoryFlags flags,
 #endif // FEATURE_METADATA_UPDATER
 }
 
-FieldDesc *Module::LookupFieldDef(mdFieldDef token)
-{
-    WRAPPER_NO_CONTRACT;
-    _ASSERTE(TypeFromToken(token) == mdtFieldDef);
-    return m_FieldDefToDescMap.GetElement(RidFromToken(token));
-}
-
 #endif // DACCESS_COMPILE
 
 

src/coreclr/vm/ceeload.h

@@ -1278,18 +1278,7 @@ class Module : public ModuleBase
 #endif // !DACCESS_COMPILE
 #endif // FEATURE_CODE_VERSIONING
 
-#ifndef DACCESS_COMPILE
-    FieldDesc *LookupFieldDef(mdFieldDef token)
-    {
-        WRAPPER_NO_CONTRACT;
-
-        _ASSERTE(TypeFromToken(token) == mdtFieldDef);
-        return m_FieldDefToDescMap.GetElement(RidFromToken(token));
-    }
-#else // DACCESS_COMPILE
-    // FieldDesc isn't defined at this point so PTR_FieldDesc can't work.
     FieldDesc *LookupFieldDef(mdFieldDef token);
-#endif // DACCESS_COMPILE
 
 #ifndef DACCESS_COMPILE
     void EnsureFieldDefCanBeStored(mdFieldDef token)

src/coreclr/vm/ceeload.inl

@@ -271,7 +271,34 @@ inline PTR_MethodDesc Module::LookupMethodDef(mdMethodDef token)
     CONTRACTL_END
 
     _ASSERTE(TypeFromToken(token) == mdtMethodDef);
-    return m_MethodDefToDescMap.GetElement(RidFromToken(token));
+    PTR_MethodDesc pResult = m_MethodDefToDescMap.GetElement(RidFromToken(token));
+    if (pResult == NULL)
+    {
+        MemoryBarrier(); // m_MethodDefToDescMap is initialized in a specific order with regard to the m_TypeDefToDescMap, and is used
+                        // by reading the TypeDefToDescMap, and then if a value is found in there, reading from this map.
+                        // Since those two reads are not dependent on each other it is possible for the compiler or CPU to reorder them.
+                        // The MemoryBarrier here prevents that reordering.
+
+        pResult = m_MethodDefToDescMap.GetElement(RidFromToken(token));
+    }
+    return pResult;
+}
+
+FieldDesc *Module::LookupFieldDef(mdFieldDef token)
+{
+    WRAPPER_NO_CONTRACT;
+    _ASSERTE(TypeFromToken(token) == mdtFieldDef);
+    FieldDesc* pResult = m_FieldDefToDescMap.GetElement(RidFromToken(token));
+
+    if (pResult == NULL)
+    {
+        MemoryBarrier(); // m_FieldDefToDescMap is initialized in a specific order with regard to the m_TypeDefToDescMap, and is used
+                     // by reading the TypeDefToDescMap, and then if a value is found in there, reading from this map.
+                     // Since those two reads are not dependent on each other it is possible for the compiler or CPU to reorder them.
+                     // The MemoryBarrier here prevents that reordering.
+        pResult = m_FieldDefToDescMap.GetElement(RidFromToken(token));
+    }
+    return pResult;
 }
 
 #ifdef FEATURE_CODE_VERSIONING