PREEMPT-RT Locking Infrastructure Possibly Ready For Linux 5.15

Six dozen patches working on the PREEMPT-RT locking infrastructure for real-time kernels is now queued up in TIP's "locking/core" branch and will presumably be sent in for the Linux 5.15 merge window coming up quickly.

These 72 patches are part of the Linux real-time (RT) work by Thomas Gleixner and others. This locking infrastructure work for real-time kernel builds is replacing mutex, ww_mutex, rw_semaphore, spinlock, and rwlock with RT-Mutex-based primitives. For non-real-time kernel builds there should be no functional changes with these locking changes.

These PREEMPT-RT locking patches were queued up on Tuesday in locking/core and represent much of the PREEMPT-RT locking infrastructure. The patches have already gone through five rounds of review and given that they have been queued up here under tip/tip.git, it looks like this work should land in Linux 5.15 that will see its merge window open up around the end of the month.

While mainlining of the Linux real-time patches has been a topic talked about for a while, it was held up due to resources/funding but over the summer we've begun to see more patches flowing so hopefully it won't be too long before that day is reached where all the RT patches have made it to mainline. The locking patches make up a large part of the remaining work but as can be seen from linux-rt-devel's patches there still is more RT work to be upstreamed.