Realtime preemption locking core merged

- memory management: The bulk of those changes sits in the akpm tree and hopefully makes 5.15-rc1

- printk: Another batch is destined for 5.15-rc1, but we still have a few steps to overcome there. Most of the technical issues have been solved, but there are quite some details to sort

- fs/namespace: The last trylock loop which causes headache. A few attempts have been made before and we're still twisting our brains around it

The rest is the tail of small changes here and there, but nothing fundamental anymore.