Thanks Jérémie,
I ran toolforge jobs flush, which stopped all jobs apparently, and removed everything from my list of jobs.
I ran toolforge jobs load to reload my list of jobs.
So it seems things are back to normal now, but I have a few questions :
* How is it possible that there was 2 instances of the same cron job ? Is it because one was stuck more than a week and a second one was started at this time ?
* How can I really stop a job (I see only toolforge commands for restarting) when it gets stuck ?
* How can I stop jobs when there are several instances of the same cron job ?
Nicolas