[PATCHSET sched_ext/scx-misc-a] sched_ext: Add @sch parameter in preparation for multi-sched support

[Tejun Heo <tj@kernel.org>]

This patchset systematically adds the @sch parameter to various sched_ext
functions in preparation for multiple scheduler support. This part is
needed regardless of how the rest of the multiple scheduler patchset
develops. The changes also remove a bunch of naked scx_root dereferences
that trigger sparse warnings. The changes are mostly mechanical parameter
additions without functional changes.

The patches are based on sched_ext/for-6.18 (ac6772e8bcda) +
"sched_ext: misc cleanups and improvements"
(http://lkml.kernel.org/r/20250922013246.275031-1-tj@kernel.org).

 1 sched_ext: Separate out scx_kick_cpu() and add @sch to it
 2 sched_ext: Add the @sch parameter to __bstr_format()
 3 sched_ext: Add the @sch parameter to ext_idle helpers
 4 sched_ext: Drop kf_cpu_valid()
 5 sched_ext: Add the @sch parameter to scx_dsq_insert_preamble/commit()
 6 sched_ext: Drop scx_kf_exit() and scx_kf_error()
 7 sched_ext: Misc updates around scx_sched instance pointer

The following git tree also contains the patchset:

  git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git scx-sub-sched-misc-prep

 kernel/sched/ext.c      | 355 ++++++++++++++++++++++++++++++------------------
 kernel/sched/ext_idle.c | 146 ++++++++++++++++----
 2 files changed, 340 insertions(+), 161 deletions(-)

--
tejun