time_second vs. time_uptime

[Jung-uk Kim]

If I read the source correctly, time_second can go backwards or 
forwards when there is a leap second but time_uptime cannot.  Am I 
right?  If my assumption is right, it seems we have some misuses in 
kernel, e. g., sched_sync() in sys/kern/vfs_subr.c.  It may not be 
critical but it worries me a little because a leap second is 
scheduled to occur at the end of this year. ;-)

Thanks,

Jung-uk Kim