Sometimes jobs get blocked by each other or "deadlock". We must manually cancel and restart the builds.

IRC Transcript
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amrox: Hello. I had a brief exchange with @jenkins on twitter yesterday http://dl.dropbox.com/u/45634/Screen%20Shot%202011-09-08%20at%205.18.05%20PM.png
amrox: my jenkins fell into a "deadlock" state again
amrox: it's still in that state now. what information can I provide?
rtyler: *nudges kohsuke *
rtyler: amrox: I'm @jenkinsci FWIW
amrox: rtyler: hi, and thanks for the responses yesterday
amrox: heres a screen recording... best way I could think to show the issue http://dl.dropbox.com/u/45634/Screen%20Recording%204.mov
farshidghods left the room (quit: Quit: Leaving.). (5:30:12 PM)
mconigliaro left the room (quit: Quit: mconigliaro). (5:30:16 PM)
amrox: I think it can be solved by just adding another executor
amrox: but I'd like to avoid that, and it seems like a bug?
kohsuke: amrox: we need thread dump. see https://wiki.jenkins-ci.org/display/JENKINS/Build+is+hanging
amrox: jenkins master dump: http://dl.dropbox.com/u/45634/threaddump.html
amrox: slave: http://dl.dropbox.com/u/45634/slave-threaddump.html
amrox: is that format acceptable? helpful at all?
amrox: should I just file a bug?
kennethreitz kennethre@c-24-127-96-129.hsd1.va.comcast.net entered the room. (5:45:36 PM)
kohsuke: amrox: yes, that'd be great
kohsuke: jenkins-admin: create ant-plugin on github for kohsuke
kohsuke: jenkins-admin: create javadoc-plugin on github for kohsuke
amrox: kohsuke: will do thanks
kohsuke: Is "content_viewer_ios_develop_build" the hanging job?
kohsuke: OK, so the issue is that the matrix parents are blocking the execution of its child builds
kohsuke: but the parent is also waiting for the completion of the child builds, hence the dead lock
kohsuke: amrox: ^^ did I get that right?
kohsuke: the question is why content_asset_verify_auto build is occupying an executor
amrox: yes that seems accurate
kohsuke: content_viewer_ios_develop_build is correctly using a temporary flyweight executor
kohsuke: ... as seen by the lack of number in the executor table
kohsuke: amrox: I assume all those builds are tried to remote-macslave-1
amrox: kohsuke: yes
kohsuke: OK. We'll capture this in the ticket you'll create
kohsuke: Thanks for bringing this to our attention, and sorry for the bug
amrox: thanks for building and maintaining jenkins