"redirfs" for example. It was file system filtering driver. AFAIK it's development ceased around 2014 and it's sudden lack in kernels caused problems for Linux's antivirus software. Suddenly your AV stopped working after you upgraded and it was that. Take an program using that module and it won't work. Such examples are probably plentiful. Since Linux kernel has stuff added to it and removed from it all the time.
No announcement yet.
Oracle Switching Solaris To A Continuous Delivery Model