From 52478777b37ba56bb11d40025df0a03ef65c6acb Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 17 Jul 2026 22:12:20 -1000 Subject: cgroup: Add cgroup_task_notifier and task migration events A subsystem can attach to the cgroup hierarchy itself, independent of which controllers are enabled where - BPF hooks already behave this way and sched_ext sub-schedulers do too. Controller callbacks can't track task migrations for them: sched_ext must re-home a task whose migration crosses a sub-scheduler boundary, but the cpu controller's attach callbacks fire only when the task_group changes and miss moves whenever the controller topology is coarser than the sub-scheduler topology. Add cgroup_task_notifier with per-task migration events mirroring the can_attach/attach/cancel_attach phases so that a consumer which prepares per-task state can also veto a migration: CGROUP_TASK_MIGRATING fires pre-commit, CGROUP_TASK_MIGRATED post-commit and CGROUP_TASK_MIGRATE_CANCELED unwinds a failed migration. Only migrations that change a task's dfl cgroup are reported. Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi --- include/linux/cgroup.h | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) (limited to 'include/linux/cgroup.h') diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index f2aa46a4f871..aa92db5f05de 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -82,12 +82,38 @@ enum cgroup_lifetime_events { CGROUP_LIFETIME_OFFLINE, }; +/* + * Events on cgroup_task_notifier, data is struct cgroup_task_migrate_ctx. + * MIGRATING fires per task before the migration commits and an error return + * from the chain fails the migration, in which case tasks that were already + * notified receive MIGRATE_CANCELED. MIGRATED fires per task after the + * migration is committed and can't fail. Only migrations that change a task's + * dfl cgroup are reported. + */ +enum cgroup_task_events { + CGROUP_TASK_MIGRATING, + CGROUP_TASK_MIGRATED, + CGROUP_TASK_MIGRATE_CANCELED, +}; + +/* + * @src_dcgrp and @dst_dcgrp are @task's dfl cgroups before and after the + * migration. @src_dcgrp is NULL for CGROUP_TASK_MIGRATED as per-task sources + * are not tracked past the commit point. + */ +struct cgroup_task_migrate_ctx { + struct task_struct *task; + struct cgroup *src_dcgrp; + struct cgroup *dst_dcgrp; +}; + extern struct file_system_type cgroup_fs_type; extern struct cgroup_root cgrp_dfl_root; extern struct css_set init_css_set; extern struct mutex cgroup_mutex; extern spinlock_t css_set_lock; extern struct blocking_notifier_head cgroup_lifetime_notifier; +extern struct blocking_notifier_head cgroup_task_notifier; #define SUBSYS(_x) extern struct cgroup_subsys _x ## _cgrp_subsys; #include -- cgit v1.2.3