We have a Hudson project 'trunk' configured to use CVS (+ Use update, + Legacy
mode) and triggered by mail notifications, more or less as described here:

https://hudson.dev.java.net/build.html

For the most part this has worked fine. However it seems that there is a build
hung now. The dashboard page claims trunk is building, and there is a pending
build for it too, yet no executor claims to be building it. (So I cannot kill
the build. I am logged in.) The project page confirms that it is being built,
#61. (The build start time is a couple of days past, as of this writing.) The
console shows it at the end of a CVS update (the mentioned file is in the
alphabetically last module to be updated) but the build command has not started
yet. No changelog available yet; probably the hang is in changelog generation,
which is deathly slow.

It is not so unusual for CVS operations to hang when run against our server; who
knows what bugs exist in our CVS server (operated by CollabNet). But why does no
executor claim to be running this build, so it cannot be killed?

In order to fix the problem I had to log in to the Hudson server machine and
restart Tomcat. Then I could ask to build trunk manually, and it starts as job
#62 (no sign of #61).