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Josh Boyer of the Fedora Project reports
[In Linux kernel 4.0], there is one feature that people (and various media sites) seem to have keyed in on and that is the live patching functionality. This holds the promise of being able to patch your running kernel without rebooting. Indeed, this could be very useful, but it isn't quite there yet. And it also doesn't make a whole lot of sense for Fedora at this time. The Fedora kernels have this functionality disabled, both in Fedora 22 and Rawhide.
What was merged for 4.0 is the core functionality that is shared between two live patching projects, kPatch and kGraft. kPatch is being led by a development team in Red Hat whereas kGraft is being developed by a team from SuSE. They both accomplish the same end result, but they do so via a different approach internally. The two teams met at the Linux Plumbers conference last year and worked on some common ground to make it easier to merge into mainline rather than compete with each other. This is absolutely awesome and an example of how new features should be developed upstream. Kudos to all those involved on that front.
The in-kernel code can accept patches from both methods, but the process and tools to create those patches are still being worked on in their upstream communities. Neither set are in Fedora itself, and likely won't be for some time as it is still fairly early in the life of these projects. After discussing this a bit with the live patching maintainer, we decided to keep this disabled in the Fedora kernels for now. The kernel-playground COPR does have it enabled for those that want to dig in and generate their own patches and are willing to break things and support themselves.
In reality, we might not ever really leverage the live patching functionality in Fedora itself.
(Score: 5, Interesting) by MichaelDavidCrawford on Tuesday May 12 2015, @05:07AM
with the machine debugger.
You can live-patch any linux kernel that supports kdb or kgdb.
While I expect that "supported" live patching will be a lot easier than using a debugger, I'm not so sure it's a good idea. If it's so important to live patch that you don't want to reboot, then you don't want to patch at all, because the reason you don't want to reboot is that you don't want to take a production box offline.
If your box is that important, then you'll want to test the patch on some other boxen.
There is also the concern that your patch might work while live, but screw up after a reboot.
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