If you are testing a Cron functionality or your Cron is stuck, there is a simple way to stop it.
If you have Drush installed:
$ drush vdel cron_semaphore $ drush vdel cron_last
Running SQL queries:
DELETE FROM `variable` WHERE name = 'cron_semaphore'; DELETE FROM `variable` WHERE name = 'cron_last';
If you have a Cron wrapper module like Elysia Cron you'll need to lookup in "elysia_cron" table and delete desired Cron process:
DELETE from elysia_cron where name='your_cron_process_name';