Comment 2 for bug 1443677

StacktraceTop:
 __GI___pthread_mutex_lock (mutex=0x0) at ../nptl/pthread_mutex_lock.c:66
 stubSyncThreadProc (ThreadSelf=0x96ced0, pvUser=<optimized out>) at /build/buildd/virtualbox-4.3.10-dfsg/src/VBox/Additions/common/crOpenGL/load.c:898
 rtThreadMain (pThread=0x96ced0, NativeThread=<optimized out>, pszThreadName=<optimized out>) at /build/buildd/virtualbox-4.3.10-dfsg/src/VBox/Runtime/common/misc/thread.cpp:712
 rtThreadNativeMain (pvArgs=0x96ced0) at /build/buildd/virtualbox-4.3.10-dfsg/src/VBox/Runtime/r3/posix/thread-posix.cpp:324
 start_thread (arg=0x7f806e2cc700) at pthread_create.c:312