[PATCHSET v2 sched_ext/for-6.19] sched_ext: Fix SCX_KICK_WAIT reliability

[PATCHSET v2 sched_ext/for-6.19] sched_ext: Fix SCX_KICK_WAIT reliability

[Tejun Heo]

SCX_KICK_WAIT is used to synchronously wait for the target CPU to complete
a reschedule and can be used to implement operations like core scheduling.
However, recent scheduler refactorings broke its reliability. This series
fixes the issue and improves the code clarity.

v2: - In patch #2, also increment pnt_seq in pick_task_scx() to handle
      same-task re-selection (Andrea Righi).
    - In patch #2, use smp_cond_load_acquire() for the busy-wait loop for
      better architecture optimization (Peter Zijlstra).
    - Added patch #3 to rename pnt_seq to kick_sync for clarity.

v1: http://lkml.kernel.org/r/20251021210354.89570-1-tj@kernel.org

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

 1 sched_ext: Don't kick CPUs running higher classes
 2 sched_ext: Fix SCX_KICK_WAIT to work reliably
 3 sched_ext: Rename pnt_seq to kick_sync

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

 kernel/sched/ext.c          | 129 ++++++++++++++++++++++++--------------------
 kernel/sched/ext_internal.h |   6 ++-
 kernel/sched/sched.h        |   2 +-
 3 files changed, 75 insertions(+), 62 deletions(-)

--
tejun