sched_ext: Reject sub-sched attachment to a disabled parent

scx_claim_exit() propagates exits to descendants under scx_sched_lock.
A sub-sched being attached concurrently could be missed if it links
after the propagation. Check the parent's exit_kind in scx_link_sched()
under scx_sched_lock to interlock against scx_claim_exit() - either the
parent sees the child in its iteration or the child sees the parent's
non-NONE exit_kind and fails attachment.

Fixes: ebeca1f930 ("sched_ext: Introduce cgroup sub-sched support")
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
This commit is contained in:
Tejun Heo 2026-03-10 07:12:21 -10:00
commit 6b4576b097