[3.1] Protect against a rare invalid lock acquision attempt during etw processing during shutdown

src/vm/ceemain.cpp

@@ -1323,6 +1323,10 @@ void STDMETHODCALLTYPE EEShutDownHelper(BOOL fIsDllUnloading)
 
     if (fIsDllUnloading)
     {
+        // The process is detaching, so set the global state.
+        // This is used to get around FreeLibrary problems.
+        g_fProcessDetach = true;
+
         ETW::EnumerationLog::ProcessShutdown();
     }
 
@@ -1339,11 +1343,6 @@ void STDMETHODCALLTYPE EEShutDownHelper(BOOL fIsDllUnloading)
     Thread * pThisThread = GetThread();
 #endif
 
-    // If the process is detaching then set the global state.
-    // This is used to get around FreeLibrary problems.
-    if(fIsDllUnloading)
-        g_fProcessDetach = true;
-
     if (IsDbgHelperSpecialThread())
     {
         // Our debugger helper thread does not allow Thread object to be set up.

src/vm/prestub.cpp

@@ -1197,6 +1197,17 @@ PrepareCodeConfig::JitOptimizationTier PrepareCodeConfig::GetJitOptimizationTier
     _ASSERTE(methodDesc != nullptr);
     _ASSERTE(config == nullptr || methodDesc == config->GetMethodDesc());
 
+    // The code below may take one or more locks. If process detach has already occurred, then other threads would have already
+    // been abruptly terminated, which may have left locks orphaned, so it would not be feasible to attempt taking a lock on
+    // process detach. This function is called from ETW-related code on shutdown where unfortunately it processes and sends
+    // rundown events upon process detach. If process detach has already occurred, then resort to best-effort behavior that may
+    // return inaccurate information. This is a temporary and targeted fix for a clear problem, and should not be used
+    // long-term.
+    if (g_fProcessDetach)
+    {
+        return JitOptimizationTier::Unknown;
+    }
+
     if (config != nullptr)
     {
         if (config->JitSwitchedToMinOpt())