Even logging can sometimes be enough to hide the heisgenbug.

Logging to a file descriptor can sometimes be avoided by logging to memory (which for crash-safety includes the possibility of an mmap’ed file, since the kernel will just take care of them as long as the whole system doesn’t go down). But logging from every thread to a single section of memory can also be problematic (even without mutexes, atomics can be expensive and certainly have side-effects) - sometimes you need a separate per-thread log, and combine in the log-reader tool.