Linux kernel patching is hard. Kpatch is a free and open source feature of the Linux kernel. It allows live patching of a running Linux server i.e. Linux kernel pachted while server is up and running to avoid downtime.
From the blog post:
Live or dynamic kernel patching allows you to patch a running kernel with no impact to running applications and without rebooting the system. Since the announcement and release of Linux kernel version 4, live kernel patching got got a lot of extra attention. Most probably this is because there weren’t a lot of big changes that one would expect with an increase in the version number. While v4 of the kernel does introduce some new stuff related to live or dynamic kernel patching, Live kernel patching was and is already available for earlier kernel releases. In this post, I’ll try to explain the differences between the new and old method and more important how to do live patching of a v3 kernel on CentOS 7.