Linux
When a leap second occurred, CLOCK_REALTIME was rewound by one second. This was not done via a mechanism that would update hrtimer base.offset. This meant that when a timer interrupt happened, TIMER_ABSTIME CLOCK_REALTIME timers got expired one second early, including timers set for less than one second. This caused applications that used sleep for less than one second in a loop to spinwait without sleeping, causing high load on many systems. This caused a large number of web services to go down in 2012.