The current 3-week Kernel SRU cycle is reasonably responsive but prone to interruptions from urgent CVEs, urgent customer requests and regressions found in -updates or during testing. It is very common for the start of any SRU cycle to be disrupted by these factors and for the cycle to have to be extended. This makes it challenging to deliver some CVE fixes in a timely manner.
In order to improve our kernel SRU release cadence velocity and predictability, the Canonical Kernel Team is transitioning from the 3-week cycle to a new 4/2 Kernel SRU Cycle. That is, a 4-week standard stable update cycle, containing the regular upstream stable updates as well as security and bug fixes and feature requests, combined with an additional planned update to be released at the 2-week midpoint of the following 4-week cycle. This “/2” update will contain only CVE fixes rated critical or high and/or other time sensitive critical customer fixes that are deemed unlikely to cause regressions.
With the new schedule, we are aiming to release fixes for critical and high CVEs and any other critical fixes on a 2-week cadence. The “/2” security/critical update being released on top of a previously released standard stable update cycle is to ensure the critical fixes are not held up by any issues/regressions in the new “4” stable cycle.
After the 2-week midpoint releases are published (at the beginning of the third week), there will be another opportunity window for re-spins in the 4-week cycle for regression fixes and/or additional urgent fixes. This mid-cycle re-spin is expected to be particularly useful for kernels that require quick turnaround times to meet project deadlines (e.g. OEM kernels).
The following picture represents how the “4/2” cycles would overlap over time, with kernels being released after the end of the preparation/test period.
The OEM kernels will follow a more flexible schedule in terms of their deadlines for the acceptance of new patches. While the cutoff dates for patches for the generic kernels are set to the last Wednesday before the start of the cycle (Week 0), to accommodate for urgent hardware fixes the OEM kernels will accept patches until Friday of Week 0 for the “/2” update and until Friday of Week 1 for the “4” stable update. The exact dates for the OEM kernels will be published together with the general Kernel SRU Cycles schedule.
With the new SRU cycle schedule, the Canonical Kernel Team is expecting to deliver more predictable updates with quicker turnaround for time sensitive fixes.
The up-to-date Kernel SRU Cycles schedule can be found at https://kernel.ubuntu.com/ and the latest schedule updates and general announcements will be published on Ubuntu Discourse “Kernel SRU” sub-category (https://discourse.ubuntu.com/c/kernel/kernel-sru/127).