Add rq lock tracking to sched_ext ops callbacks to enable scx_bpf_*()
kfuncs to detect whether a specific rq is currently locked and safely
operate with it.

If no rq is locked, the target rq lock can be acquired. If a different rq
is already locked, the operation can either fail (triggering an ops error),
deferred using IRQ work, or managed accordingly to avoid deadlocks.

This patchset is also available in the following git branch:

 git://git.kernel.org/pub/scm/linux/kernel/git/arighi/linux.git scx-rq-lock-tracking

Changes in v2:
 - store currently locked rq in a percpu variable
 - link to v1: https://lore.kernel.org/all/20250419123536.154469-1-arighi@nvidia.com

Andrea Righi (2):
      sched_ext: Track currently locked rq
      sched_ext: Fix missing rq lock in scx_bpf_cpuperf_set()

 kernel/sched/ext.c      | 163 ++++++++++++++++++++++++++++++++----------------
 kernel/sched/ext_idle.c |   2 +-
 2 files changed, 110 insertions(+), 55 deletions(-)