Re: [PATCH v2 0/1] MR5236: ntdll: Implement NtdllDefWindowProc_A().

[Jinoh Kang (＠iamahuman)]

Jinoh Kang (@iamahuman) commented about dlls/ntdll/misc.c:
> - UNICODE_STRING name;
> - NTSTATUS status;
> - HMODULE module;
> -
> - if (pDefWindowProcA) return pDefWindowProcA( hwnd, msg, wParam, lParam );
> -
> - RtlCreateUnicodeString( &name, L"user32.dll" );
> - if (( status = LdrLoadDll( NULL, 0, &name, &module )))
> - {
> -
>    ERR("Failed to load user32.dll, status %ld\n", status);
> -
>    if (name.Buffer) RtlFreeUnicodeString( &name );
> -
>    return 1; /* FIXME: Is this a good way to indicate failure? */
> - }
> -
> - if (name.Buffer) RtlFreeUnicodeString( &name );
> - pDefWindowProcA = RtlFindExportedRoutineByName( module, "DefWindowProcA" );

This leads to data race, since nothing prevents `NtdllDefWindowProc_A` from being called by multiple threads. Since we don't want to keep user32.dll loaded (this should be the application's responsibility), `pDefWindowProcA` should be a local variable instead (i.e., no caching, no `static`).