libthread_xu: FAULT VALUE CHANGE

[Gennady Proskurin <gprspb@xxxxxxx>]

I triggered the following message printed so stderr for my
program (C++, boost::asio, threads, SMP/2cpu)

thr_umtx_wait: FAULT VALUE CHANGE 0 -> 1 oncond 0x282f0314
thr_umtx_wait: FAULT VALUE CHANGE 0 -> 1 oncond 0x282f0344
thr_umtx_wait: FAULT VALUE CHANGE 0 -> 1 oncond 0x282f032c

What is it?  I found lines in source doing fprintf
(libthread_xu/thread/thr_umtx.c, line 140), but I not quite
understand what happens. Is it harmful and worth debugging,
or I should just ignore this?

2.6-RELEASE DragonFly v2.6.3.43.gb67e7