On his blog, Josh Boyer looks at the choice of the 4.0 kernel for Fedora 22. While the underpinnings of the live kernel patching feature have been merged, even when it is fully operational it is probably not something that Fedora (and perhaps other distributions) will use often (or at all). "In reality, we might not ever really leverage the live patching functionality in Fedora itself. It is understandable that people want to patch their kernel without rebooting, but the mechanism is mostly targeted at small bugfixes and security patches. You cannot, for example, live patch from version 4.0 to 4.1. Given that the Fedora kernel rebases both from stable kernel (e.g. 3.19.2 to 3.19.3) and major release kernels over the lifetime of a Fedora release, we don't have much opportunity to build the live patches."
April 16, 2015
Boyer: Fedora 22 and Kernel 4.0
Read more at LWN