If you run a flow
this deletes the control directory for the shell step while it is running, and it becomes impossible to abort the build.
I think this is because FileMonitoringController.exitStatus just checks if jenkins-result.txt exists yet. But if the whole control dir is missing, it should return -1 or similar.
Similar effect if you botch the $PATH so that echo cannot be found. In that case the control dir is present, but pid is not, so the controller assumes the process is still starting! It should impose a time limit on the startup phase.
Was ameliorated by improving DurableTaskExecution.stop to do a hard kill if you try to stop the build twice. This makes the similar
JENKINS-25678 much less of a problem.