[PATCH v2 0/8] Replace PREEMPT_RT ifdefs with preempt_[dis|en]able_nested().

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

Folks,

this is v2 of "Replace PREEMPT_RT ifdefs with preempt_[dis|en]able_nested()."
The v1 is at
   https://lore.kernel.org/all/20220817162703.728679-1-bigeasy@linutronix.de/

v1…v2:
   - The SLUB patch got s/use_lockless_fast_path/USE_LOCKLESS_FAST_PATH/ as
     Linus asked for and was handed over to Vlastimil and is sitting in his
     slab tree:
        https://git.kernel.org/vbabka/slab/c/591570a7

   - The compaction patch got an "depends on COMPACTION" so it is not listed
     .config if compaction is disabled (Rasmus Villemoes).

   - The removal of u64_stats_fetch_begin_irq() has been excluded from the
     series and staged for later. Jakub asked for this, so that it can be
     included in later merge window.

   - A patch for flex_proportions has been added which also needs a
     preempt_disable_nested() since the merge window.

Original cover letter:

this is the follow up to the "vfs.git pile 3 - dcache" pull request [0].
It was concluded that the introduction of
	preempt_disable_nested()

in general makes sense and should be used in places where preemption on
!RT is disabled by other means and PREEMPT_RT need to explicitly disable
it.

This series introduces the macro and converts already existing users to
that macro. The u64_stat interface was simplified to make the change
simpler and code easier to follow.

[0] https://lore.kernel.org/all/YurA3aSb4GRr4wlW@ZenIV/

Sebastian