[$] BPF and the realtime patch set

Back in July, Linus Torvalds merged a patchin the 5.3 merge windowthat added the PREEMPT_RT option to the kernel build-time configuration.That was meant as a signal that the realtime patch set was moving from its longtime status asout-of-tree code to a fully supported kernel feature. As the code behindthe configuration option makes its way into the mainline, some friction canbe expected; we are seeing a bit of that now with respect to the BPF subsystem.