Online patching, also known as live or dynamic patching, is a technology that allows one to patch a running Linux kernel without any downtime or affecting the running applications. Online patching is desirable as it eliminates the need for scheduled maintenance due to patches and allows for patching in a timelier manner.
With these goals in mind, this talk will introduce our current efforts investigating online patches for the Lustre filesystem. The current technology of choice is “kpatch,” a popular dynamic kernel patching system from Redhat. Kpatch technology works by registering “ftrace” no-op to call a new function instead of the original function. It also modifies the address to return to the new function effectively by-passing the older one.
Kpatch works very well on a single node/machine. However, when attempting to patch multiple nodes/machines, care must be exercised to ensure that all of them are indeed running the modified patch. If a patch fails on a node/server, that failure must be identified and the patch must be tried again. Our current approach to solving this issue is a wrapper program around kpatch that makes sure not only that everything is upgraded, but that it may be listed, verified, and rolled back if necessary. This talk intends to include a demonstration of the proposed technique, showing a system that needs to be patched without downtime, the commands used to patch and verify the patch on all nodes/machines, and the system running applications that are ultimately able to keep running despite the patching.
