From a6ec0b62c589c5b5518e0e3d9eaac6398a82b6f4 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 17 Jul 2026 22:12:20 -1000 Subject: sched_ext: Hand over cgroups at sub-scheduler enable/disable Sub-schedulers don't get cgroups yet: every task_group is inited on the root sched and the routing added by the previous patches always resolves to it. Add the handover: an enabling sub-scheduler takes over the cgroups in its subtree and a disabling one returns them to its parent. scx_cgroup_claim_subtree() runs while the sub enables, after the subtree's cgrp->scx_sched's are set and before any task is claimed. It inits each subtree task_group on the sub, exits it from the parent and updates tg->scx.sched. A failed ops.cgroup_init() unwinds the sub-side inits and aborts the enable with the parent untouched. Disabling reverses it with scx_cgroup_return_subtree(): exit each cgroup from the sub, then re-init it on the parent with the current tg->scx.* values, resyncing weight and bandwidth changes made while the sub had it. When a re-init fails, the parent is failed and the remaining task_groups still transfer uninited and get no cgroup ops - the same punting done for tasks. The dying parent's own disable moves them onward. The handover walks include dying but not yet offlined task_groups, the same as root's bulk walks: a removed cgroup keeps hosting scheduling events until its dying tasks finish their final context switches, and its ops.cgroup_exit() must follow the last of them. tg on/offlining is excluded through cgroup_lock(), so either ordering against an rmdir of a subtree cgroup delivers balanced init/exit pairs. Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi --- include/linux/sched/ext.h | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'include') diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h index a6db5d300f30..78b2f289cb98 100644 --- a/include/linux/sched/ext.h +++ b/include/linux/sched/ext.h @@ -298,6 +298,19 @@ static inline bool scx_rcu_cpu_stall(const struct cpumask *stalled_mask) { retur struct scx_task_group { #ifdef CONFIG_EXT_GROUP_SCHED + /* + * The sched this tg is on, NULL if none. SCX_TG_INITED tracks whether + * ops.cgroup_init() succeeded on it. When a child sched exits and its + * tgs move to the parent, a failed init leaves the tg on the parent + * with INITED clear (see scx_cgroup_return_subtree()). + * + * This is tracked separately from cgrp->scx_sched because the tg + * hierarchy can diverge from the cgroup2 hierarchy in both lifetime and + * shape. A tg stays online past its cgroup's removal while the + * cgrp->scx_sched rewrites visit only live cgroups, leaving a removed + * cgroup's pointer stale. The cpu controller can also be mounted on + * cgroup1. + */ struct scx_sched *sched; u32 flags; /* SCX_TG_* */ -- cgit v1.2.3