We had a number of linked projects which could be removed.

I opened multiple projects in multiple tabpages and deleted them.
I did not get reaction of the server (timeout).

Later on all kind of changes to jobs failed.

The cron thread was blocked as well, so no new jobs were started.

I was able to create a thread dump.

Most methods hang on hudson.model.Project.getPublishersList() this is synchronized method.

The deadlock message:

"Handling POST /jenkins/job/cws-is-junit-l/doDelete : RequestHandlerThread20":
waiting to lock Monitor@0x000000000c447fa8 (Object@0x0000000747c7aaf0, a hudson/model/FreeStyleProject),
which is held by "Handling POST /jenkins/job/prepare-for-is-regressions/doDelete : RequestHandlerThread15"
"Handling POST /jenkins/job/prepare-for-is-regressions/doDelete : RequestHandlerThread15":
waiting to lock Monitor@0x000000000b3e3c68 (Object@0x0000000747ec1378, a hudson/model/FreeStyleProject),
which is held by "Handling POST /jenkins/job/cws-is-junit-l/doDelete : RequestHandlerThread20"

The 2 jobs are up and downstream jobs of eachother.