[PATCHSET sched_ext/for-6.19] sched_ext: Fix SCX_KICK_WAIT reliability

[Tejun Heo <tj@kernel.org>]

SCX_KICK_WAIT is used to synchronously wait for a target CPU to complete a
reschedule, which is needed for implementing operations like core scheduling.
This broke when scx_next_task_picked() was replaced with switch_class() in
commit b999e365c298, because the sequence counter increment that SCX_KICK_WAIT
depends on was no longer reliably called.

This patchset fixes the regression by moving the sequence counter update to
put_prev_task_scx() and refining the semantics to work correctly with the
updated scheduler structure. The first patch adds a prerequisite check to
skip kicking CPUs running higher sched classes, which SCX has no control over.

Based on sched_ext/for-6.19 (2dbbdeda77a6).

 0001 sched_ext: Don't kick CPUs running higher classes
 0002 sched_ext: Fix SCX_KICK_WAIT to work reliably

Git tree: git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git scx-fix-kick_wait

 kernel/sched/ext.c          | 42 ++++++++++++++++++++++++++----------------
 kernel/sched/ext_internal.h |  6 ++++--
 2 files changed, 30 insertions(+), 18 deletions(-)
--
tejun