[$] Local locks in the kernel

The Linux kernel has never lacked for synchronization primitives andlocking mechanisms, so one might justifiably wonder why there might be aneed to add another one. The addition of locallocks to 5.8 provides an answer to that question. These locks,which have their origin in the realtime (PREEMPT_RT) tree, werecreated to solve some realtime-specific problems, but they also bring somemuch-needed structure to a common locking pattern used in non-realtimekernels as well.