In  JDK-6900441 we fixed the park implementation on Linux to use CLOCK_MONOTONIC  using pthread_condattr_setclock, which is now required to be available on all supported Linux platforms. However we also allowed for it to fail at runtime:

+  // Only set the clock if CLOCK_MONOTONIC is available
+  if (Linux::supports_monotonic_clock()) {
+    if ((status = pthread_condattr_setclock(_condattr, CLOCK_MONOTONIC)) != 0) {
+      if (status == EINVAL) {
+        warning("Unable to use monotonic clock with relative timed-waits" \
+                " - changes to the time-of-day clock may have adverse affects");
+      } else {
+        fatal(err_msg("pthread_condattr_setclock: %s", strerror(status)));
+      }
+    }
+  }

If we do hit the EINVAL case we simply print the warning, but computeAbsTime and unpackTime will still calculate relative timeouts using CLOCK_MONOTONIC, which is wrong if the pthread_cond_timedwait is actually going to use CLOCK_REALTIME.