[PATCHSET v2 sched_ext/for-7.3] sched_ext: Sub-scheduler and cid fixes

[Tejun Heo]

Hello,

v2: v1's 0003 only added NULL checks and, as Andrea and sashiko-bot pointed
    out, left the cid tables readable while being filled and rewritten in
    place. The new 0004 replaces it: each root enable builds a fresh table
    set privately and publishes it with RCU once the layout is final. 0003
    is a new trivial dead code removal. 0001-0002 are unchanged.

v1: https://lore.kernel.org/r/20260720082605.1451945-1-tj@xxxxxxxxxx

A few fixes for the sub-scheduler and cid-form code on for-7.3.

- 0001 attributes a runnable stall to the scheduler that owns the DSQ the
  task is stuck on rather than the task's owner, so a bypassing sub's task
  parked on an ancestor's bypass DSQ blames the ancestor, not the sub.

- 0002 skips the default CPU selection while bypassing. The pick is discarded
  by the bypass enqueue anyway, and it consults idle masks a scheduler doing
  its own idle tracking leaves frozen.

- 0003 drops the unused scx_cpumask_to_cmask().

- 0004 ties the cid tables' lifetimes to the root sched: built privately on
  enable, published with RCU once final, unpublished and RCU-freed on
  disable.

Based on sched_ext/for-7.3 (b20dfde5ec54).

Tejun Heo (4):
  sched_ext: Blame the DSQ's owning scheduler for a runnable stall
  sched_ext: Skip the default CPU selection while bypassing
  sched_ext: Drop unused scx_cpumask_to_cmask()
  sched_ext: Build the cid tables privately and publish them with RCU

Git tree: git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git scx-sub-fixes-v2

 kernel/sched/ext/cid.c      | 279 ++++++++++++++++++++++++++------------------
 kernel/sched/ext/cid.h      |  58 +++++----
 kernel/sched/ext/ext.c      |  80 ++++++++++---
 kernel/sched/ext/internal.h |   5 +-
 kernel/sched/ext/sub.c      |  42 +++++--
 5 files changed, 298 insertions(+), 166 deletions(-)

--
tejun