SCM Polling / Max # of concurrent polling = 1 hangs github polling

after a while process list shows a lot of entries like this, for each project in jenkins

jenkins 18383 0.0 0.0 6208 1192 ? S 17:09 0:00 git fetch -t git@github.com:carrot-garden/carrot-util.git +refs/heads/:refs/remotes/origin/
jenkins 18388 0.0 0.0 6300 2332 ? S 17:09 0:00 ssh git@github.com git-upload-pack 'carrot-garden/carrot-util.git'

which appear to be in hang state;

github scm polling works no more;

resolution - periodic
"killall git ssh"