[PATCH v2 0/8] kernel/fork: Move thread stack free otu of the scheduler path.

[Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>]

This is a follup-up on the patch
    sched: Delay task stack freeing on RT 
    https://lkml.kernel.org/r/20210928122411.593486363@xxxxxxxxxxxxx

It addresses the review feedback:
- Decouple stack accounting from its free invocation. The accounting
  happens in do_exit(), the final free call happens later.

- Add put_task_stack_sched() to finish_task_switch(). Here the VMAP
  stack is cached only. If it fails, or in the !VMAP case then the final
  free happens in delayed_put_task_struct(). This is also an oportunity
  to cache the stack.

Changes since v1:
  - Drop the bit marked und use addtional RCU head to free the stack in
  case that it can't be cached. Suggested by Andy Lutomirski.

v1: https://lore.kernel.org/all/20220125152652.1963111-1-bigeasy@xxxxxxxxxxxxx