Merge branch 'for-next' of https://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git

19 files changed, 1299 insertions, 1184 deletions

diff --git a/drivers/hid/hid-asus.c b/drivers/hid/hid-asus.c
index 3f5e96900b67..d34d74df3dc0 100644
--- a/drivers/hid/hid-asus.c
+++ b/drivers/hid/hid-asus.c
@@ -965,6 +965,12 @@ static int asus_input_configured(struct hid_device *hdev, struct hid_input *hi)
 		}
 	}
 
+	if (drvdata->quirks & QUIRK_HID_FN_LOCK) {
+		drvdata->fn_lock = true;
+		INIT_WORK(&drvdata->fn_lock_sync_work, asus_sync_fn_lock);
+		asus_kbd_set_fn_lock(hdev, true);
+	}
+
 	if (drvdata->tp) {
 		int ret;
 
diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
index 20b2343aa344..75cb8b119fb7 100644
--- a/include/linux/sched/ext.h
+++ b/include/linux/sched/ext.h
@@ -263,7 +263,7 @@ void sched_ext_dead(struct task_struct *p);
 void print_scx_info(const char *log_lvl, struct task_struct *p);
 void scx_softlockup(u32 dur_s);
 bool scx_hardlockup(int cpu);
-bool scx_rcu_cpu_stall(void);
+bool scx_rcu_cpu_stall(const struct cpumask *stalled_mask);
 
 #else	/* !CONFIG_SCHED_CLASS_EXT */
 
@@ -271,7 +271,7 @@ static inline void sched_ext_dead(struct task_struct *p) {}
 static inline void print_scx_info(const char *log_lvl, struct task_struct *p) {}
 static inline void scx_softlockup(u32 dur_s) {}
 static inline bool scx_hardlockup(int cpu) { return false; }
-static inline bool scx_rcu_cpu_stall(void) { return false; }
+static inline bool scx_rcu_cpu_stall(const struct cpumask *stalled_mask) { return false; }
 
 #endif	/* CONFIG_SCHED_CLASS_EXT */
 
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 03a43d3d2616..415583c35f8c 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4900,6 +4900,9 @@ static void __init rcu_dump_rcu_node_tree(void)
 
 struct workqueue_struct *rcu_gp_wq;
 
+static struct cpumask rcu_stall_cpumask;
+static struct cpumask rcu_exp_stall_cpumask;
+
 void __init rcu_init(void)
 {
 	int cpu = smp_processor_id();
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 82cada459e5d..46b6907f1b09 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -578,6 +578,7 @@ static void synchronize_rcu_expedited_stall(unsigned long jiffies_start, unsigne
 			if (!(READ_ONCE(rnp->expmask) & mask))
 				continue;
 			ndetected++;
+			cpumask_set_cpu(cpu, &rcu_exp_stall_cpumask);
 			rdp = per_cpu_ptr(&rcu_data, cpu);
 			pr_cont(" %d-%c%c%c%c", cpu,
 				"O."[!!cpu_online(cpu)],
@@ -665,6 +666,8 @@ static void synchronize_rcu_expedited_wait(void)
 		if (rcu_stall_is_suppressed())
 			continue;
 
+		cpumask_clear(&rcu_exp_stall_cpumask);
+
 		nbcon_cpu_emergency_enter();
 
 		j = jiffies;
@@ -675,7 +678,7 @@ static void synchronize_rcu_expedited_wait(void)
 
 		nbcon_cpu_emergency_exit();
 
-		panic_on_rcu_stall();
+		panic_on_rcu_stall(&rcu_exp_stall_cpumask);
 	}
 }
 
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index cf7ae51cba40..ebf381936eb1 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -159,7 +159,7 @@ static int __init check_cpu_stall_init(void)
 early_initcall(check_cpu_stall_init);
 
 /* If so specified via sysctl, panic, yielding cleaner stall-warning output. */
-static void panic_on_rcu_stall(void)
+static void panic_on_rcu_stall(const struct cpumask *stalled_mask)
 {
 	static int cpu_stall;
 
@@ -167,7 +167,7 @@ static void panic_on_rcu_stall(void)
 	 * Attempt to kick out the BPF scheduler if it's installed and defer
 	 * the panic to give the system a chance to recover.
 	 */
-	if (scx_rcu_cpu_stall())
+	if (scx_rcu_cpu_stall(stalled_mask))
 		return;
 
 	if (++cpu_stall < sysctl_max_rcu_stall_to_panic)
@@ -644,6 +644,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 	if (rcu_stall_is_suppressed())
 		return;
 
+	cpumask_clear(&rcu_stall_cpumask);
+
 	nbcon_cpu_emergency_enter();
 
 	/*
@@ -659,6 +661,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 			for_each_leaf_node_possible_cpu(rnp, cpu)
 				if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
 					print_cpu_stall_info(cpu);
+					cpumask_set_cpu(cpu, &rcu_stall_cpumask);
 					ndetected++;
 				}
 		}
@@ -700,7 +703,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 
 	nbcon_cpu_emergency_exit();
 
-	panic_on_rcu_stall();
+	panic_on_rcu_stall(&rcu_stall_cpumask);
 
 	rcu_force_quiescent_state();  /* Kick them all. */
 }
@@ -753,7 +756,9 @@ static void print_cpu_stall(unsigned long gp_seq, unsigned long gps)
 
 	nbcon_cpu_emergency_exit();
 
-	panic_on_rcu_stall();
+	cpumask_clear(&rcu_stall_cpumask);
+	cpumask_set_cpu(smp_processor_id(), &rcu_stall_cpumask);
+	panic_on_rcu_stall(&rcu_stall_cpumask);
 
 	/*
 	 * Attempt to revive the RCU machinery by forcing a context switch.
diff --git a/kernel/sched/build_policy.c b/kernel/sched/build_policy.c
index d74b54f81992..01dc7bf89af8 100644
--- a/kernel/sched/build_policy.c
+++ b/kernel/sched/build_policy.c
@@ -66,10 +66,12 @@
 # include "ext/cid.h"
 # include "ext/arena.h"
 # include "ext/idle.h"
+# include "ext/sub.h"
 # include "ext/ext.c"
 # include "ext/cid.c"
 # include "ext/arena.c"
 # include "ext/idle.c"
+# include "ext/sub.c"
 #endif
 
 #include "syscalls.c"
diff --git a/kernel/sched/ext/arena.c b/kernel/sched/ext/arena.c
index 5783694ec21d..b0e6a0be4913 100644
--- a/kernel/sched/ext/arena.c
+++ b/kernel/sched/ext/arena.c
@@ -70,8 +70,6 @@ void scx_arena_pool_destroy(struct scx_sched *sch)
  */
 static int scx_arena_grow(struct scx_sched *sch, u32 page_cnt)
 {
-	u64 kern_vm_start;
-	u32 uaddr32;
 	void *p;
 	int ret;
 
@@ -83,15 +81,8 @@ static int scx_arena_grow(struct scx_sched *sch, u32 page_cnt)
 	if (!p)
 		return -ENOMEM;
 
-	uaddr32 = (u32)(unsigned long)p;
-	/* arena.o, which defines these, is built only on MMU && 64BIT */
-#if defined(CONFIG_MMU) && defined(CONFIG_64BIT)
-	kern_vm_start = bpf_arena_map_kern_vm_start(sch->arena_map);
-#else
-	kern_vm_start = 0;
-#endif
-
-	ret = gen_pool_add(sch->arena_pool, kern_vm_start + uaddr32,
+	ret = gen_pool_add(sch->arena_pool,
+			   (unsigned long)scx_arena_to_kaddr(sch, p),
 			   page_cnt * PAGE_SIZE, NUMA_NO_NODE);
 	if (ret) {
 		bpf_arena_free_pages_non_sleepable(sch->arena_map, p, page_cnt);
diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index 691d53fe0f64..1a0ec985da77 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -19,8 +19,9 @@
 #include "cid.h"
 #include "arena.h"
 #include "idle.h"
+#include "sub.h"
 
-static DEFINE_RAW_SPINLOCK(scx_sched_lock);
+DEFINE_RAW_SPINLOCK(scx_sched_lock);
 
 /*
  * NOTE: sched_ext is in the process of growing multiple scheduler support and
@@ -39,14 +40,14 @@ struct scx_sched __rcu *scx_root;
 static LIST_HEAD(scx_sched_all);
 
 #ifdef CONFIG_EXT_SUB_SCHED
-static const struct rhashtable_params scx_sched_hash_params = {
+const struct rhashtable_params scx_sched_hash_params = {
 	.key_len		= sizeof_field(struct scx_sched, ops.sub_cgroup_id),
 	.key_offset		= offsetof(struct scx_sched, ops.sub_cgroup_id),
 	.head_offset		= offsetof(struct scx_sched, hash_node),
 	.insecure_elasticity	= true,	/* inserted under scx_sched_lock */
 };
 
-static struct rhashtable scx_sched_hash;
+struct rhashtable scx_sched_hash;
 #endif
 
 /* see SCX_OPS_TID_TO_TASK */
@@ -68,9 +69,9 @@ static DEFINE_RAW_SPINLOCK(scx_tasks_lock);
 static LIST_HEAD(scx_tasks);
 
 /* ops enable/disable */
-static DEFINE_MUTEX(scx_enable_mutex);
+DEFINE_MUTEX(scx_enable_mutex);
 DEFINE_STATIC_KEY_FALSE(__scx_enabled);
-DEFINE_STATIC_PERCPU_RWSEM(scx_fork_rwsem);
+DEFINE_PERCPU_RWSEM(scx_fork_rwsem);
 static atomic_t scx_enable_state_var = ATOMIC_INIT(SCX_DISABLED);
 static DEFINE_RAW_SPINLOCK(scx_bypass_lock);
 static bool scx_init_task_enabled;
@@ -101,7 +102,7 @@ static atomic64_t scx_tid_cursor = ATOMIC64_INIT(1);
  * tasks for the sub-sched being enabled. Use a global variable instead of a
  * per-task field as all enables are serialized.
  */
-static struct scx_sched *scx_enabling_sub_sched;
+struct scx_sched *scx_enabling_sub_sched;
 #else
 #define scx_enabling_sub_sched	(struct scx_sched *)NULL
 #endif	/* CONFIG_EXT_SUB_SCHED */
@@ -242,7 +243,6 @@ MODULE_PARM_DESC(bypass_lb_intv_us, "bypass load balance interval in microsecond
 
 static void run_deferred(struct rq *rq);
 static bool task_dead_and_done(struct task_struct *p);
-static void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags);
 static void scx_disable(struct scx_sched *sch, enum scx_exit_kind kind);
 
 __printf(5, 6) bool __scx_exit(struct scx_sched *sch,
@@ -272,58 +272,6 @@ static bool u32_before(u32 a, u32 b)
 	return (s32)(a - b) < 0;
 }
 
-#ifdef CONFIG_EXT_SUB_SCHED
-/**
- * scx_next_descendant_pre - find the next descendant for pre-order walk
- * @pos: the current position (%NULL to initiate traversal)
- * @root: sched whose descendants to walk
- *
- * To be used by scx_for_each_descendant_pre(). Find the next descendant to
- * visit for pre-order traversal of @root's descendants. @root is included in
- * the iteration and the first node to be visited.
- */
-static struct scx_sched *scx_next_descendant_pre(struct scx_sched *pos,
-						 struct scx_sched *root)
-{
-	struct scx_sched *next;
-
-	lockdep_assert(lockdep_is_held(&scx_enable_mutex) ||
-		       lockdep_is_held(&scx_sched_lock));
-
-	/* if first iteration, visit @root */
-	if (!pos)
-		return root;
-
-	/* visit the first child if exists */
-	next = list_first_entry_or_null(&pos->children, struct scx_sched, sibling);
-	if (next)
-		return next;
-
-	/* no child, visit my or the closest ancestor's next sibling */
-	while (pos != root) {
-		if (!list_is_last(&pos->sibling, &scx_parent(pos)->children))
-			return list_next_entry(pos, sibling);
-		pos = scx_parent(pos);
-	}
-
-	return NULL;
-}
-
-static struct scx_sched *scx_find_sub_sched(u64 cgroup_id)
-{
-	return rhashtable_lookup(&scx_sched_hash, &cgroup_id,
-				 scx_sched_hash_params);
-}
-
-static void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch)
-{
-	rcu_assign_pointer(p->scx.sched, sch);
-}
-#else	/* CONFIG_EXT_SUB_SCHED */
-static inline struct scx_sched *scx_next_descendant_pre(struct scx_sched *pos, struct scx_sched *root) { return pos ? NULL : root; }
-static inline void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch) {}
-#endif	/* CONFIG_EXT_SUB_SCHED */
-
 /**
  * scx_is_descendant - Test whether sched is a descendant
  * @sch: sched to test
@@ -338,19 +286,6 @@ static bool scx_is_descendant(struct scx_sched *sch, struct scx_sched *ancestor)
 	return sch->ancestors[ancestor->level] == ancestor;
 }
 
-/**
- * scx_for_each_descendant_pre - pre-order walk of a sched's descendants
- * @pos: iteration cursor
- * @root: sched to walk the descendants of
- *
- * Walk @root's descendants. @root is included in the iteration and the first
- * node to be visited. Must be called with either scx_enable_mutex or
- * scx_sched_lock held.
- */
-#define scx_for_each_descendant_pre(pos, root)					\
-	for ((pos) = scx_next_descendant_pre(NULL, (root)); (pos);		\
-	     (pos) = scx_next_descendant_pre((pos), (root)))
-
 static struct scx_dispatch_q *find_global_dsq(struct scx_sched *sch, s32 cpu)
 {
 	return &sch->pnode[cpu_to_node(cpu)]->global_dsq;
@@ -369,11 +304,6 @@ static const struct sched_class *scx_setscheduler_class(struct task_struct *p)
 	return __setscheduler_class(p->policy, p->prio);
 }
 
-static struct scx_dispatch_q *bypass_dsq(struct scx_sched *sch, s32 cpu)
-{
-	return &per_cpu_ptr(sch->pcpu, cpu)->bypass_dsq;
-}
-
 static struct scx_dispatch_q *bypass_enq_target_dsq(struct scx_sched *sch, s32 cpu)
 {
 #ifdef CONFIG_EXT_SUB_SCHED
@@ -392,27 +322,7 @@ static struct scx_dispatch_q *bypass_enq_target_dsq(struct scx_sched *sch, s32 c
 		sch = scx_parent(sch);
 #endif	/* CONFIG_EXT_SUB_SCHED */
 
-	return bypass_dsq(sch, cpu);
-}
-
-/**
- * bypass_dsp_enabled - Check if bypass dispatch path is enabled
- * @sch: scheduler to check
- *
- * When a descendant scheduler enters bypass mode, bypassed tasks are scheduled
- * by the nearest non-bypassing ancestor, or the root scheduler if all ancestors
- * are bypassing. In the former case, the ancestor is not itself bypassing but
- * its bypass DSQs will be populated with bypassed tasks from descendants. Thus,
- * the ancestor's bypass dispatch path must be active even though its own
- * bypass_depth remains zero.
- *
- * This function checks bypass_dsp_enable_depth which is managed separately from
- * bypass_depth to enable this decoupling. See enable_bypass_dsp() and
- * disable_bypass_dsp().
- */
-static bool bypass_dsp_enabled(struct scx_sched *sch)
-{
-	return unlikely(atomic_read(&sch->bypass_dsp_enable_depth));
+	return scx_bypass_dsq(sch, cpu);
 }
 
 /**
@@ -676,12 +586,12 @@ struct bpf_iter_scx_dsq {
 } __attribute__((aligned(8)));
 
 
-static u32 scx_get_task_state(const struct task_struct *p)
+u32 scx_get_task_state(const struct task_struct *p)
 {
 	return p->scx.flags & SCX_TASK_STATE_MASK;
 }
 
-static void scx_set_task_state(struct task_struct *p, u32 state)
+void scx_set_task_state(struct task_struct *p, u32 state)
 {
 	u32 prev_state = scx_get_task_state(p);
 	bool warn = false;
@@ -721,23 +631,6 @@ static void scx_set_task_state(struct task_struct *p, u32 state)
 	p->scx.flags |= state;
 }
 
-/*
- * SCX task iterator.
- */
-struct scx_task_iter {
-	struct sched_ext_entity		cursor;
-	struct task_struct		*locked_task;
-	struct rq			*rq;
-	struct rq_flags			rf;
-	u32				cnt;
-	bool				list_locked;
-#ifdef CONFIG_EXT_SUB_SCHED
-	struct cgroup			*cgrp;
-	struct cgroup_subsys_state	*css_pos;
-	struct css_task_iter		css_iter;
-#endif
-};
-
 /**
  * scx_task_iter_start - Lock scx_tasks_lock and start a task iteration
  * @iter: iterator to init
@@ -766,7 +659,7 @@ struct scx_task_iter {
  * All tasks which existed when the iteration started are guaranteed to be
  * visited as long as they are not dead.
  */
-static void scx_task_iter_start(struct scx_task_iter *iter, struct cgroup *cgrp)
+void scx_task_iter_start(struct scx_task_iter *iter, struct cgroup *cgrp)
 {
 	memset(iter, 0, sizeof(*iter));
 
@@ -805,7 +698,7 @@ static void __scx_task_iter_rq_unlock(struct scx_task_iter *iter)
  * This function can be safely called anytime during an iteration. The next
  * iterator operation will automatically restore the necessary locking.
  */
-static void scx_task_iter_unlock(struct scx_task_iter *iter)
+void scx_task_iter_unlock(struct scx_task_iter *iter)
 {
 	__scx_task_iter_rq_unlock(iter);
 	if (iter->list_locked) {
@@ -848,7 +741,7 @@ static void scx_task_iter_relock(struct scx_task_iter *iter,
  * which is released on return. If the iterator holds a task's rq lock, that rq
  * lock is also released. See scx_task_iter_start() for details.
  */
-static void scx_task_iter_stop(struct scx_task_iter *iter)
+void scx_task_iter_stop(struct scx_task_iter *iter)
 {
 #ifdef CONFIG_EXT_SUB_SCHED
 	if (iter->cgrp) {
@@ -923,7 +816,7 @@ static struct task_struct *scx_task_iter_next(struct scx_task_iter *iter)
  * whether they would like to filter out dead tasks. See scx_task_iter_start()
  * for details.
  */
-static struct task_struct *scx_task_iter_next_locked(struct scx_task_iter *iter)
+struct task_struct *scx_task_iter_next_locked(struct scx_task_iter *iter)
 {
 	struct task_struct *p;
 
@@ -979,42 +872,6 @@ static struct task_struct *scx_task_iter_next_locked(struct scx_task_iter *iter)
 }
 
 /**
- * scx_add_event - Increase an event counter for 'name' by 'cnt'
- * @sch: scx_sched to account events for
- * @name: an event name defined in struct scx_event_stats
- * @cnt: the number of the event occurred
- *
- * This can be used when preemption is not disabled.
- */
-#define scx_add_event(sch, name, cnt) do {					\
-	this_cpu_add((sch)->pcpu->event_stats.name, (cnt));			\
-	trace_sched_ext_event(#name, (cnt));					\
-} while(0)
-
-/**
- * __scx_add_event - Increase an event counter for 'name' by 'cnt'
- * @sch: scx_sched to account events for
- * @name: an event name defined in struct scx_event_stats
- * @cnt: the number of the event occurred
- *
- * This should be used only when preemption is disabled.
- */
-#define __scx_add_event(sch, name, cnt) do {					\
-	__this_cpu_add((sch)->pcpu->event_stats.name, (cnt));			\
-	trace_sched_ext_event(#name, cnt);					\
-} while(0)
-
-/**
- * scx_agg_event - Aggregate an event counter 'kind' from 'src_e' to 'dst_e'
- * @dst_e: destination event stats
- * @src_e: source event stats
- * @kind: a kind of event to be aggregated
- */
-#define scx_agg_event(dst_e, src_e, kind) do {					\
-	(dst_e)->kind += READ_ONCE((src_e)->kind);				\
-} while(0)
-
-/**
  * scx_dump_event - Dump an event 'kind' in 'events' to 's'
  * @s: output seq_buf
  * @events: event stats
@@ -1088,28 +945,6 @@ bool scx_cpu_valid(struct scx_sched *sch, s32 cpu, const char *where)
 	}
 }
 
-/**
- * ops_sanitize_err - Sanitize a -errno value
- * @sch: scx_sched to error out on error
- * @ops_name: operation to blame on failure
- * @err: -errno value to sanitize
- *
- * Verify @err is a valid -errno. If not, trigger scx_error() and return
- * -%EPROTO. This is necessary because returning a rogue -errno up the chain can
- * cause misbehaviors. For an example, a large negative return from
- * ops.init_task() triggers an oops when passed up the call chain because the
- * value fails IS_ERR() test after being encoded with ERR_PTR() and then is
- * handled as a pointer.
- */
-static int ops_sanitize_err(struct scx_sched *sch, const char *ops_name, s32 err)
-{
-	if (err < 0 && err >= -MAX_ERRNO)
-		return err;
-
-	scx_error(sch, "ops.%s() returned an invalid errno %d", ops_name, err);
-	return -EPROTO;
-}
-
 static void deferred_bal_cb_workfn(struct rq *rq)
 {
 	run_deferred(rq);
@@ -1196,8 +1031,8 @@ static void schedule_deferred_locked(struct rq *rq)
 	schedule_deferred(rq);
 }
 
-static void schedule_dsq_reenq(struct scx_sched *sch, struct scx_dispatch_q *dsq,
-			       u64 reenq_flags, struct rq *locked_rq)
+void schedule_dsq_reenq(struct scx_sched *sch, struct scx_dispatch_q *dsq,
+			u64 reenq_flags, struct rq *locked_rq)
 {
 	struct rq *rq;
 
@@ -1261,16 +1096,6 @@ static void schedule_dsq_reenq(struct scx_sched *sch, struct scx_dispatch_q *dsq
 		schedule_deferred(rq);
 }
 
-static void schedule_reenq_local(struct rq *rq, u64 reenq_flags)
-{
-	struct scx_sched *root = rcu_dereference_sched(scx_root);
-
-	if (WARN_ON_ONCE(!root))
-		return;
-
-	schedule_dsq_reenq(root, &rq->scx.local_dsq, reenq_flags, rq);
-}
-
 /**
  * touch_core_sched - Update timestamp used for core-sched task ordering
  * @rq: rq to read clock from, must be locked
@@ -1357,8 +1182,8 @@ static void dsq_inc_nr(struct scx_dispatch_q *dsq, struct task_struct *p, u64 en
 	 * to the CPU or dequeued. In both cases, the only way @p can go back to
 	 * the BPF sched is through enqueueing. If being inserted into a local
 	 * DSQ with IMMED, persist the state until the next enqueueing event in
-	 * do_enqueue_task() so that we can maintain IMMED protection through
-	 * e.g. SAVE/RESTORE cycles and slice extensions.
+	 * scx_do_enqueue_task() so that we can maintain IMMED protection
+	 * through e.g. SAVE/RESTORE cycles and slice extensions.
 	 */
 	if (enq_flags & SCX_ENQ_IMMED) {
 		if (unlikely(dsq->id != SCX_DSQ_LOCAL)) {
@@ -1381,7 +1206,7 @@ static void dsq_inc_nr(struct scx_dispatch_q *dsq, struct task_struct *p, u64 en
 		 * done yet, @p can't go on the CPU immediately. Re-enqueue.
 		 */
 		if (unlikely(dsq->nr > 1 || !rq_is_open(rq, enq_flags)))
-			schedule_reenq_local(rq, 0);
+			scx_schedule_reenq_local(rq, 0);
 	}
 }
 
@@ -1498,9 +1323,9 @@ static void local_dsq_post_enq(struct scx_sched *sch, struct scx_dispatch_q *dsq
 	}
 }
 
-static void dispatch_enqueue(struct scx_sched *sch, struct rq *rq,
-			     struct scx_dispatch_q *dsq, struct task_struct *p,
-			     u64 enq_flags)
+static void scx_dispatch_enqueue(struct scx_sched *sch, struct rq *rq,
+				 struct scx_dispatch_q *dsq, struct task_struct *p,
+				 u64 enq_flags)
 {
 	bool is_local = dsq->id == SCX_DSQ_LOCAL;
 
@@ -1648,7 +1473,7 @@ static void task_unlink_from_dsq(struct task_struct *p,
 	}
 }
 
-static void dispatch_dequeue(struct rq *rq, struct task_struct *p)
+static void scx_dispatch_dequeue(struct rq *rq, struct task_struct *p)
 {
 	struct scx_dispatch_q *dsq = p->scx.dsq;
 	bool is_local = dsq == &rq->scx.local_dsq;
@@ -1702,8 +1527,8 @@ static void dispatch_dequeue(struct rq *rq, struct task_struct *p)
 }
 
 /*
- * Abbreviated version of dispatch_dequeue() that can be used when both @p's rq
- * and dsq are locked.
+ * Abbreviated version of scx_dispatch_dequeue() that can be used when both
+ * @p's rq and dsq are locked.
  */
 static void dispatch_dequeue_locked(struct task_struct *p,
 				    struct scx_dispatch_q *dsq)
@@ -1784,10 +1609,10 @@ static void mark_direct_dispatch(struct scx_sched *sch,
  *  - direct_dispatch(): cleared on the synchronous enqueue path, deferred
  *    dispatch keeps the state until consumed
  *  - process_ddsp_deferred_locals(): cleared after consuming deferred state,
- *  - do_enqueue_task(): cleared on enqueue fallbacks where the dispatch
+ *  - scx_do_enqueue_task(): cleared on enqueue fallbacks where the dispatch
  *    verdict is ignored (local/global/bypass)
- *  - dequeue_task_scx(): cleared after dispatch_dequeue(), covering deferred
- *    cancellation and holding_cpu races
+ *  - dequeue_task_scx(): cleared after scx_dispatch_dequeue(), covering
+ *    deferred cancellation and holding_cpu races
  *  - scx_disable_task(): cleared for queued wakeup tasks, which are excluded by
  *    the scx_bypass() loop, so that stale state is not reused by a subsequent
  *    scheduler instance
@@ -1848,10 +1673,10 @@ static void direct_dispatch(struct scx_sched *sch, struct task_struct *p,
 	ddsp_enq_flags = p->scx.ddsp_enq_flags;
 	clear_direct_dispatch(p);
 
-	dispatch_enqueue(sch, rq, dsq, p, ddsp_enq_flags | SCX_ENQ_CLEAR_OPSS);
+	scx_dispatch_enqueue(sch, rq, dsq, p, ddsp_enq_flags | SCX_ENQ_CLEAR_OPSS);
 }
 
-static bool scx_rq_online(struct rq *rq)
+bool scx_rq_online(struct rq *rq)
 {
 	/*
 	 * Test both cpu_active() and %SCX_RQ_ONLINE. %SCX_RQ_ONLINE indicates
@@ -1863,8 +1688,8 @@ static bool scx_rq_online(struct rq *rq)
 	return likely((rq->scx.flags & SCX_RQ_ONLINE) && cpu_active(cpu_of(rq)));
 }
 
-static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags,
-			    int sticky_cpu)
+static void scx_do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags,
+				int sticky_cpu)
 {
 	struct scx_sched *sch = scx_task_sched(p);
 	struct task_struct **ddsp_taskp;
@@ -1951,7 +1776,7 @@ direct:
 	direct_dispatch(sch, p, enq_flags);
 	return;
 local_norefill:
-	dispatch_enqueue(sch, rq, &rq->scx.local_dsq, p, enq_flags);
+	scx_dispatch_enqueue(sch, rq, &rq->scx.local_dsq, p, enq_flags);
 	return;
 local:
 	dsq = &rq->scx.local_dsq;
@@ -1972,7 +1797,7 @@ enqueue:
 	touch_core_sched(rq, p);
 	refill_task_slice_dfl(sch, p);
 	clear_direct_dispatch(p);
-	dispatch_enqueue(sch, rq, dsq, p, enq_flags);
+	scx_dispatch_enqueue(sch, rq, dsq, p, enq_flags);
 }
 
 static bool task_runnable(const struct task_struct *p)
@@ -2041,7 +1866,7 @@ static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int core_enq_
 	if (rq->scx.nr_running == 1)
 		dl_server_start(&rq->ext_server);
 
-	do_enqueue_task(rq, p, enq_flags, sticky_cpu);
+	scx_do_enqueue_task(rq, p, enq_flags, sticky_cpu);
 
 	if (sticky_cpu >= 0)
 		p->scx.sticky_cpu = -1;
@@ -2177,7 +2002,7 @@ static bool dequeue_task_scx(struct rq *rq, struct task_struct *p, int core_deq_
 	rq->scx.nr_running--;
 	sub_nr_running(rq, 1);
 
-	dispatch_dequeue(rq, p);
+	scx_dispatch_dequeue(rq, p);
 	clear_direct_dispatch(p);
 	return true;
 }
@@ -2225,7 +2050,7 @@ static void wakeup_preempt_scx(struct rq *rq, struct task_struct *p, int wake_fl
 	 * - A higher-priority wakes up while SCX dispatch is in progress.
 	 */
 	if (rq->scx.nr_immed)
-		schedule_reenq_local(rq, 0);
+		scx_schedule_reenq_local(rq, 0);
 }
 
 static void move_local_task_to_local_dsq(struct scx_sched *sch,
@@ -2307,6 +2132,7 @@ static void move_remote_task_to_local_dsq(struct task_struct *p, u64 enq_flags,
  *   no to the BPF scheduler initiated migrations while offline.
  *
  * The caller must ensure that @p and @rq are on different CPUs.
+ * If enforce == true, caller must hold @p's rq lock.
  */
 static bool task_can_run_on_remote_rq(struct scx_sched *sch,
 				      struct task_struct *p, struct rq *rq,
@@ -2314,6 +2140,14 @@ static bool task_can_run_on_remote_rq(struct scx_sched *sch,
 {
 	s32 cpu = cpu_of(rq);
 
+	/*
+	 * To prevent races with @p still running on its old CPU while switching
+	 * out, make sure we're holding @p's rq lock so as not to risk
+	 * erroneously killing the BPF scheduler.
+	 */
+	if (enforce)
+		lockdep_assert_rq_held(task_rq(p));
+
 	WARN_ON_ONCE(task_cpu(p) == cpu);
 
 	/*
@@ -2381,7 +2215,7 @@ static bool task_can_run_on_remote_rq(struct scx_sched *sch,
  * values afterwards, as this operation can't be preempted or recurse, the
  * holding_cpu can never become this CPU again before we're done. Thus, we can
  * tell whether we lost to dequeue by testing whether the holding_cpu still
- * points to this CPU. See dispatch_dequeue() for the counterpart.
+ * points to this CPU. See scx_dispatch_dequeue() for the counterpart.
  *
  * On return, @dsq is unlocked and @src_rq is locked. Returns %true if @p is
  * still valid. %false if lost to dequeue.
@@ -2486,14 +2320,14 @@ static struct rq *move_task_between_dsqs(struct scx_sched *sch,
 		dispatch_dequeue_locked(p, src_dsq);
 		raw_spin_unlock(&src_dsq->lock);
 
-		dispatch_enqueue(sch, dst_rq, dst_dsq, p, enq_flags);
+		scx_dispatch_enqueue(sch, dst_rq, dst_dsq, p, enq_flags);
 	}
 
 	return dst_rq;
 }
 
-static bool consume_dispatch_q(struct scx_sched *sch, struct rq *rq,
-			       struct scx_dispatch_q *dsq, u64 enq_flags)
+bool scx_consume_dispatch_q(struct scx_sched *sch, struct rq *rq,
+			    struct scx_dispatch_q *dsq, u64 enq_flags)
 {
 	struct task_struct *p;
 retry:
@@ -2539,11 +2373,11 @@ retry:
 	return false;
 }
 
-static bool consume_global_dsq(struct scx_sched *sch, struct rq *rq)
+bool scx_consume_global_dsq(struct scx_sched *sch, struct rq *rq)
 {
 	int node = cpu_to_node(cpu_of(rq));
 
-	return consume_dispatch_q(sch, rq, &sch->pnode[node]->global_dsq, 0);
+	return scx_consume_dispatch_q(sch, rq, &sch->pnode[node]->global_dsq, 0);
 }
 
 /**
@@ -2576,15 +2410,8 @@ static void dispatch_to_local_dsq(struct scx_sched *sch, struct rq *rq,
 	 * If dispatching to @rq that @p is already on, no lock dancing needed.
 	 */
 	if (rq == src_rq && rq == dst_rq) {
-		dispatch_enqueue(sch, rq, dst_dsq, p,
-				 enq_flags | SCX_ENQ_CLEAR_OPSS);
-		return;
-	}
-
-	if (src_rq != dst_rq &&
-	    unlikely(!task_can_run_on_remote_rq(sch, p, dst_rq, true))) {
-		dispatch_enqueue(sch, rq, find_global_dsq(sch, task_cpu(p)), p,
-				 enq_flags | SCX_ENQ_CLEAR_OPSS | SCX_ENQ_GDSQ_FALLBACK);
+		scx_dispatch_enqueue(sch, rq, dst_dsq, p,
+				     enq_flags | SCX_ENQ_CLEAR_OPSS);
 		return;
 	}
 
@@ -2614,6 +2441,7 @@ static void dispatch_to_local_dsq(struct scx_sched *sch, struct rq *rq,
 	/* task_rq couldn't have changed if we're still the holding cpu */
 	if (likely(p->scx.holding_cpu == raw_smp_processor_id()) &&
 	    !WARN_ON_ONCE(src_rq != task_rq(p))) {
+		bool fallback = false;
 		/*
 		 * If @p is staying on the same rq, there's no need to go
 		 * through the full deactivate/activate cycle. Optimize by
@@ -2621,8 +2449,13 @@ static void dispatch_to_local_dsq(struct scx_sched *sch, struct rq *rq,
 		 */
 		if (src_rq == dst_rq) {
 			p->scx.holding_cpu = -1;
-			dispatch_enqueue(sch, dst_rq, &dst_rq->scx.local_dsq, p,
-					 enq_flags);
+			scx_dispatch_enqueue(sch, dst_rq, &dst_rq->scx.local_dsq, p,
+					     enq_flags);
+		} else if (unlikely(!task_can_run_on_remote_rq(sch, p, dst_rq, true))) {
+			p->scx.holding_cpu = -1;
+			fallback = true;
+			scx_dispatch_enqueue(sch, src_rq, find_global_dsq(sch, task_cpu(p)),
+					     p, enq_flags | SCX_ENQ_GDSQ_FALLBACK);
 		} else {
 			move_remote_task_to_local_dsq(p, enq_flags,
 						      src_rq, dst_rq);
@@ -2631,7 +2464,7 @@ static void dispatch_to_local_dsq(struct scx_sched *sch, struct rq *rq,
 		}
 
 		/* if the destination CPU is idle, wake it up */
-		if (sched_class_above(p->sched_class, dst_rq->curr->sched_class))
+		if (!fallback && sched_class_above(p->sched_class, dst_rq->curr->sched_class))
 			resched_curr(dst_rq);
 	}
 
@@ -2710,10 +2543,10 @@ retry:
 		goto retry;
 	case SCX_OPSS_QUEUEING:
 		/*
-		 * do_enqueue_task() is in the process of transferring the task
-		 * to the BPF scheduler while holding @p's rq lock. As we aren't
-		 * holding any kernel or BPF resource that the enqueue path may
-		 * depend upon, it's safe to wait.
+		 * scx_do_enqueue_task() is in the process of transferring the
+		 * task to the BPF scheduler while holding @p's rq lock. As we
+		 * aren't holding any kernel or BPF resource that the enqueue
+		 * path may depend upon, it's safe to wait.
 		 */
 		wait_ops_state(p, opss);
 		goto retry;
@@ -2726,10 +2559,10 @@ retry:
 	if (dsq->id == SCX_DSQ_LOCAL)
 		dispatch_to_local_dsq(sch, rq, dsq, p, enq_flags);
 	else
-		dispatch_enqueue(sch, rq, dsq, p, enq_flags | SCX_ENQ_CLEAR_OPSS);
+		scx_dispatch_enqueue(sch, rq, dsq, p, enq_flags | SCX_ENQ_CLEAR_OPSS);
 }
 
-static void flush_dispatch_buf(struct scx_sched *sch, struct rq *rq)
+void scx_flush_dispatch_buf(struct scx_sched *sch, struct rq *rq)
 {
 	struct scx_dsp_ctx *dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx;
 	u32 u;
@@ -2758,115 +2591,6 @@ static inline void maybe_queue_balance_callback(struct rq *rq)
 	rq->scx.flags &= ~SCX_RQ_BAL_CB_PENDING;
 }
 
-/*
- * One user of this function is scx_bpf_dispatch() which can be called
- * recursively as sub-sched dispatches nest. Always inline to reduce stack usage
- * from the call frame.
- */
-static __always_inline bool
-scx_dispatch_sched(struct scx_sched *sch, struct rq *rq,
-		   struct task_struct *prev, bool nested)
-{
-	struct scx_dsp_ctx *dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx;
-	int nr_loops = SCX_DSP_MAX_LOOPS;
-	s32 cpu = cpu_of(rq);
-	bool prev_on_sch = (prev->sched_class == &ext_sched_class) &&
-		scx_task_on_sched(sch, prev);
-
-	if (consume_global_dsq(sch, rq))
-		return true;
-
-	if (bypass_dsp_enabled(sch)) {
-		/* if @sch is bypassing, only the bypass DSQs are active */
-		if (scx_bypassing(sch, cpu))
-			return consume_dispatch_q(sch, rq, bypass_dsq(sch, cpu), 0);
-
-#ifdef CONFIG_EXT_SUB_SCHED
-		/*
-		 * If @sch isn't bypassing but its children are, @sch is
-		 * responsible for making forward progress for both its own
-		 * tasks that aren't bypassing and the bypassing descendants'
-		 * tasks. The following implements a simple built-in behavior -
-		 * let each CPU try to run the bypass DSQ every Nth time.
-		 *
-		 * Later, if necessary, we can add an ops flag to suppress the
-		 * auto-consumption and a kfunc to consume the bypass DSQ and,
-		 * so that the BPF scheduler can fully control scheduling of
-		 * bypassed tasks.
-		 */
-		struct scx_sched_pcpu *pcpu = per_cpu_ptr(sch->pcpu, cpu);
-
-		if (!(pcpu->bypass_host_seq++ % SCX_BYPASS_HOST_NTH) &&
-		    consume_dispatch_q(sch, rq, bypass_dsq(sch, cpu), 0)) {
-			__scx_add_event(sch, SCX_EV_SUB_BYPASS_DISPATCH, 1);
-			return true;
-		}
-#endif	/* CONFIG_EXT_SUB_SCHED */
-	}
-
-	if (unlikely(!SCX_HAS_OP(sch, dispatch)) || !scx_rq_online(rq))
-		return false;
-
-	dspc->rq = rq;
-
-	/*
-	 * The dispatch loop. Because flush_dispatch_buf() may drop the rq lock,
-	 * the local DSQ might still end up empty after a successful
-	 * ops.dispatch(). If the local DSQ is empty even after ops.dispatch()
-	 * produced some tasks, retry. The BPF scheduler may depend on this
-	 * looping behavior to simplify its implementation.
-	 */
-	do {
-		dspc->nr_tasks = 0;
-
-		if (nested) {
-			SCX_CALL_OP(sch, dispatch, rq, scx_cpu_arg(cpu),
-				    prev_on_sch ? prev : NULL);
-		} else {
-			/* stash @prev so that nested invocations can access it */
-			rq->scx.sub_dispatch_prev = prev;
-			SCX_CALL_OP(sch, dispatch, rq, scx_cpu_arg(cpu),
-				    prev_on_sch ? prev : NULL);
-			rq->scx.sub_dispatch_prev = NULL;
-		}
-
-		flush_dispatch_buf(sch, rq);
-
-		if ((prev->scx.flags & SCX_TASK_QUEUED) && prev->scx.slice) {
-			rq->scx.flags |= SCX_RQ_BAL_KEEP;
-			return true;
-		}
-		if (rq->scx.local_dsq.nr)
-			return true;
-		if (consume_global_dsq(sch, rq))
-			return true;
-
-		/*
-		 * ops.dispatch() can trap us in this loop by repeatedly
-		 * dispatching ineligible tasks. Break out once in a while to
-		 * allow the watchdog to run. As IRQ can't be enabled in
-		 * balance(), we want to complete this scheduling cycle and then
-		 * start a new one. IOW, we want to call resched_curr() on the
-		 * next, most likely idle, task, not the current one. Use
-		 * __scx_bpf_kick_cpu() for deferred kicking.
-		 */
-		if (unlikely(!--nr_loops)) {
-			scx_kick_cpu(sch, cpu, 0);
-			break;
-		}
-	} while (dspc->nr_tasks);
-
-	/*
-	 * Prevent the CPU from going idle while bypassed descendants have tasks
-	 * queued. Without this fallback, bypassed tasks could stall if the host
-	 * scheduler's ops.dispatch() doesn't yield any tasks.
-	 */
-	if (bypass_dsp_enabled(sch))
-		return consume_dispatch_q(sch, rq, bypass_dsq(sch, cpu), 0);
-
-	return false;
-}
-
 static int balance_one(struct rq *rq, struct task_struct *prev)
 {
 	struct scx_sched *sch = scx_root;
@@ -2941,7 +2665,7 @@ has_tasks:
 	 *   between the IMMED queueing and the subsequent scheduling event.
 	 */
 	if (unlikely(rq->scx.local_dsq.nr > 1 && rq->scx.nr_immed))
-		schedule_reenq_local(rq, 0);
+		scx_schedule_reenq_local(rq, 0);
 
 	rq->scx.flags &= ~SCX_RQ_IN_BALANCE;
 	return true;
@@ -2957,7 +2681,7 @@ static void set_next_task_scx(struct rq *rq, struct task_struct *p, bool first)
 		 * dispatched. Call ops_dequeue() to notify the BPF scheduler.
 		 */
 		ops_dequeue(rq, p, SCX_DEQ_CORE_SCHED_EXEC);
-		dispatch_dequeue(rq, p);
+		scx_dispatch_dequeue(rq, p);
 	}
 
 	p->se.exec_start = rq_clock_task(rq);
@@ -3069,10 +2793,10 @@ static void put_prev_task_scx(struct rq *rq, struct task_struct *p,
 		if (p->scx.slice && !scx_bypassing(sch, cpu_of(rq))) {
 			if (p->scx.flags & SCX_TASK_IMMED) {
 				p->scx.flags |= SCX_TASK_REENQ_PREEMPTED;
-				do_enqueue_task(rq, p, SCX_ENQ_REENQ, -1);
+				scx_do_enqueue_task(rq, p, SCX_ENQ_REENQ, -1);
 				p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK;
 			} else {
-				dispatch_enqueue(sch, rq, &rq->scx.local_dsq, p, SCX_ENQ_HEAD);
+				scx_dispatch_enqueue(sch, rq, &rq->scx.local_dsq, p, SCX_ENQ_HEAD);
 			}
 			goto switch_class;
 		}
@@ -3082,12 +2806,17 @@ static void put_prev_task_scx(struct rq *rq, struct task_struct *p,
 		 * sched_class, %SCX_OPS_ENQ_LAST must be set. Tell
 		 * ops.enqueue() that @p is the only one available for this cpu,
 		 * which should trigger an explicit follow-up scheduling event.
+		 *
+		 * Core scheduling can force this CPU idle while @p stays
+		 * runnable. @p's cookie then won't match the core's, so skip
+		 * the warning in that case.
 		 */
 		if (next && sched_class_above(&ext_sched_class, next->sched_class)) {
-			WARN_ON_ONCE(!(sch->ops.flags & SCX_OPS_ENQ_LAST));
-			do_enqueue_task(rq, p, SCX_ENQ_LAST, -1);
+			WARN_ON_ONCE(sched_cpu_cookie_match(rq, p) &&
+				     !(sch->ops.flags & SCX_OPS_ENQ_LAST));
+			scx_do_enqueue_task(rq, p, SCX_ENQ_LAST, -1);
 		} else {
-			do_enqueue_task(rq, p, 0, -1);
+			scx_do_enqueue_task(rq, p, 0, -1);
 		}
 	}
 
@@ -3545,7 +3274,7 @@ static struct cgroup *tg_cgrp(struct task_group *tg)
 
 #endif	/* CONFIG_EXT_GROUP_SCHED */
 
-static int __scx_init_task(struct scx_sched *sch, struct task_struct *p, bool fork)
+int __scx_init_task(struct scx_sched *sch, struct task_struct *p, bool fork)
 {
 	int ret;
 
@@ -3559,7 +3288,7 @@ static int __scx_init_task(struct scx_sched *sch, struct task_struct *p, bool fo
 
 		ret = SCX_CALL_OP_RET(sch, init_task, NULL, p, &args);
 		if (unlikely(ret)) {
-			ret = ops_sanitize_err(sch, "init_task", ret);
+			ret = scx_ops_sanitize_err(sch, "init_task", ret);
 			return ret;
 		}
 	}
@@ -3628,7 +3357,7 @@ static void __scx_enable_task(struct scx_sched *sch, struct task_struct *p)
 		SCX_CALL_OP_TASK(sch, set_weight, rq, p, p->scx.weight);
 }
 
-static void scx_enable_task(struct scx_sched *sch, struct task_struct *p)
+void scx_enable_task(struct scx_sched *sch, struct task_struct *p)
 {
 	__scx_enable_task(sch, p);
 	scx_set_task_state(p, SCX_TASK_ENABLED);
@@ -3648,6 +3377,13 @@ static void scx_disable_task(struct scx_sched *sch, struct task_struct *p)
 	scx_set_task_state(p, SCX_TASK_READY);
 
 	/*
+	 * Reset the SCX-managed fields when @p leaves the BPF scheduler's
+	 * control, after ops.disable() has observed their final values.
+	 */
+	p->scx.dsq_vtime = 0;
+	p->scx.slice = 0;
+
+	/*
 	 * Verify the task is not in BPF scheduler's custody. If flag
 	 * transitions are consistent, the flag should always be clear
 	 * here.
@@ -3655,8 +3391,7 @@ static void scx_disable_task(struct scx_sched *sch, struct task_struct *p)
 	WARN_ON_ONCE(p->scx.flags & SCX_TASK_IN_CUSTODY);
 }
 
-static void __scx_disable_and_exit_task(struct scx_sched *sch,
-					struct task_struct *p)
+void __scx_disable_and_exit_task(struct scx_sched *sch, struct task_struct *p)
 {
 	struct scx_exit_task_args args = {
 		.cancelled = false,
@@ -3690,7 +3425,7 @@ static void __scx_disable_and_exit_task(struct scx_sched *sch,
  * ran. The task state has not been transitioned, so this mirrors the
  * SCX_TASK_INIT branch in __scx_disable_and_exit_task().
  */
-static void scx_sub_init_cancel_task(struct scx_sched *sch, struct task_struct *p)
+void scx_sub_init_cancel_task(struct scx_sched *sch, struct task_struct *p)
 {
 	struct scx_exit_task_args args = { .cancelled = true };
 
@@ -3701,8 +3436,7 @@ static void scx_sub_init_cancel_task(struct scx_sched *sch, struct task_struct *
 		SCX_CALL_OP_TASK(sch, exit_task, task_rq(p), p, &args);
 }
 
-static void scx_disable_and_exit_task(struct scx_sched *sch,
-				      struct task_struct *p)
+void scx_disable_and_exit_task(struct scx_sched *sch, struct task_struct *p)
 {
 	__scx_disable_and_exit_task(sch, p);
 
@@ -4097,7 +3831,7 @@ static u32 reenq_local(struct scx_sched *sch, struct rq *rq, u64 reenq_flags)
 		if (!local_task_should_reenq(p, &reenq_flags, &reason))
 			continue;
 
-		dispatch_dequeue(rq, p);
+		scx_dispatch_dequeue(rq, p);
 
 		if (WARN_ON_ONCE(p->scx.flags & SCX_TASK_REENQ_REASON_MASK))
 			p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK;
@@ -4109,7 +3843,7 @@ static u32 reenq_local(struct scx_sched *sch, struct rq *rq, u64 reenq_flags)
 	list_for_each_entry_safe(p, n, &tasks, scx.dsq_list.node) {
 		list_del_init(&p->scx.dsq_list.node);
 
-		do_enqueue_task(rq, p, SCX_ENQ_REENQ, -1);
+		scx_do_enqueue_task(rq, p, SCX_ENQ_REENQ, -1);
 
 		p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK;
 		nr_enqueued++;
@@ -4224,7 +3958,7 @@ static void reenq_user(struct rq *rq, struct scx_dispatch_q *dsq, u64 reenq_flag
 			p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK;
 		p->scx.flags |= reason;
 
-		do_enqueue_task(task_rq, p, SCX_ENQ_REENQ, -1);
+		scx_do_enqueue_task(task_rq, p, SCX_ENQ_REENQ, -1);
 
 		p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK;
 
@@ -4344,7 +4078,7 @@ int scx_tg_online(struct task_group *tg)
 			ret = SCX_CALL_OP_RET(sch, cgroup_init,
 					      NULL, tg->css.cgroup, &args);
 			if (ret)
-				ret = ops_sanitize_err(sch, "cgroup_init", ret);
+				ret = scx_ops_sanitize_err(sch, "cgroup_init", ret);
 		}
 		if (ret == 0)
 			tg->scx.flags |= SCX_TG_ONLINE | SCX_TG_INITED;
@@ -4412,7 +4146,7 @@ err:
 		p->scx.cgrp_moving_from = NULL;
 	}
 
-	return ops_sanitize_err(sch, "cgroup_prep_move", ret);
+	return scx_ops_sanitize_err(sch, "cgroup_prep_move", ret);
 }
 
 void scx_cgroup_move_task(struct task_struct *p)
@@ -4515,7 +4249,7 @@ static struct cgroup *root_cgroup(void)
 	return &cgrp_dfl_root.cgrp;
 }
 
-static void scx_cgroup_lock(void)
+void scx_cgroup_lock(void)
 {
 #ifdef CONFIG_EXT_GROUP_SCHED
 	percpu_down_write(&scx_cgroup_ops_rwsem);
@@ -4523,7 +4257,7 @@ static void scx_cgroup_lock(void)
 	cgroup_lock();
 }
 
-static void scx_cgroup_unlock(void)
+void scx_cgroup_unlock(void)
 {
 	cgroup_unlock();
 #ifdef CONFIG_EXT_GROUP_SCHED
@@ -4536,26 +4270,6 @@ static inline void scx_cgroup_lock(void) {}
 static inline void scx_cgroup_unlock(void) {}
 #endif	/* CONFIG_EXT_GROUP_SCHED || CONFIG_EXT_SUB_SCHED */
 
-#ifdef CONFIG_EXT_SUB_SCHED
-static struct cgroup *sch_cgroup(struct scx_sched *sch)
-{
-	return sch->cgrp;
-}
-
-/* for each descendant of @cgrp including self, set ->scx_sched to @sch */
-static void set_cgroup_sched(struct cgroup *cgrp, struct scx_sched *sch)
-{
-	struct cgroup *pos;
-	struct cgroup_subsys_state *css;
-
-	cgroup_for_each_live_descendant_pre(pos, css, cgrp)
-		rcu_assign_pointer(pos->scx_sched, sch);
-}
-#else	/* CONFIG_EXT_SUB_SCHED */
-static inline struct cgroup *sch_cgroup(struct scx_sched *sch) { return NULL; }
-static inline void set_cgroup_sched(struct cgroup *cgrp, struct scx_sched *sch) {}
-#endif	/* CONFIG_EXT_SUB_SCHED */
-
 /*
  * Omitted operations:
  *
@@ -4690,7 +4404,7 @@ static void destroy_dsq(struct scx_sched *sch, u64 dsq_id)
 		goto out_unlock_dsq;
 
 	/*
-	 * Mark dead by invalidating ->id to prevent dispatch_enqueue() from
+	 * Mark dead by invalidating ->id to prevent scx_dispatch_enqueue() from
 	 * queueing more tasks. As this function can be called from anywhere,
 	 * freeing is bounced through an irq work to avoid nesting RCU
 	 * operations inside scheduler locks.
@@ -4838,8 +4552,10 @@ static const struct attribute_group scx_global_attr_group = {
 
 static void free_pnode(struct scx_sched_pnode *pnode);
 static void free_exit_info(struct scx_exit_info *ei);
+static const char *scx_exit_reason(enum scx_exit_kind kind);
+static bool scx_claim_exit(struct scx_sched *sch, enum scx_exit_kind kind);
 
-static s32 scx_set_cmask_scratch_alloc(struct scx_sched *sch)
+s32 scx_set_cmask_scratch_alloc(struct scx_sched *sch)
 {
 	size_t size = struct_size_t(struct scx_cmask, bits,
 				    SCX_CMASK_NR_WORDS(num_possible_cpus()));
@@ -4894,6 +4610,7 @@ static void scx_sched_free_rcu_work(struct work_struct *work)
 	timer_shutdown_sync(&sch->bypass_lb_timer);
 	free_cpumask_var(sch->bypass_lb_donee_cpumask);
 	free_cpumask_var(sch->bypass_lb_resched_cpumask);
+	free_cpumask_var(sch->stall_cpus);
 
 #ifdef CONFIG_EXT_SUB_SCHED
 	kfree(sch->cgrp_path);
@@ -4901,6 +4618,8 @@ static void scx_sched_free_rcu_work(struct work_struct *work)
 		cgroup_put(sch_cgroup(sch));
 	if (sch->sub_kset)
 		kobject_put(&sch->sub_kset->kobj);
+	if (scx_parent(sch))
+		kobject_put(&scx_parent(sch)->kobj);
 #endif	/* CONFIG_EXT_SUB_SCHED */
 
 	for_each_possible_cpu(cpu) {
@@ -4913,7 +4632,7 @@ static void scx_sched_free_rcu_work(struct work_struct *work)
 		 */
 		WARN_ON_ONCE(!list_empty(&pcpu->deferred_reenq_local.node));
 
-		exit_dsq(bypass_dsq(sch, cpu));
+		exit_dsq(scx_bypass_dsq(sch, cpu));
 	}
 
 	free_percpu(sch->pcpu);
@@ -4971,19 +4690,9 @@ static ssize_t scx_attr_events_show(struct kobject *kobj,
 	int at = 0;
 
 	scx_read_events(sch, &events);
-	at += scx_attr_event_show(buf, at, &events, SCX_EV_SELECT_CPU_FALLBACK);
-	at += scx_attr_event_show(buf, at, &events, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE);
-	at += scx_attr_event_show(buf, at, &events, SCX_EV_DISPATCH_KEEP_LAST);
-	at += scx_attr_event_show(buf, at, &events, SCX_EV_ENQ_SKIP_EXITING);
-	at += scx_attr_event_show(buf, at, &events, SCX_EV_ENQ_SKIP_MIGRATION_DISABLED);
-	at += scx_attr_event_show(buf, at, &events, SCX_EV_REENQ_IMMED);
-	at += scx_attr_event_show(buf, at, &events, SCX_EV_REENQ_LOCAL_REPEAT);
-	at += scx_attr_event_show(buf, at, &events, SCX_EV_REFILL_SLICE_DFL);
-	at += scx_attr_event_show(buf, at, &events, SCX_EV_BYPASS_DURATION);
-	at += scx_attr_event_show(buf, at, &events, SCX_EV_BYPASS_DISPATCH);
-	at += scx_attr_event_show(buf, at, &events, SCX_EV_BYPASS_ACTIVATE);
-	at += scx_attr_event_show(buf, at, &events, SCX_EV_INSERT_NOT_OWNED);
-	at += scx_attr_event_show(buf, at, &events, SCX_EV_SUB_BYPASS_DISPATCH);
+#define SCX_EVENT(name)	(at += scx_attr_event_show(buf, at, &events, name))
+	SCX_EVENTS_LIST(SCX_EVENT);
+#undef SCX_EVENT
 	return at;
 }
 SCX_ATTR(events);
@@ -5077,6 +4786,7 @@ bool scx_allow_ttwu_queue(const struct task_struct *p)
 
 /**
  * handle_lockup - sched_ext common lockup handler
+ * @exit_cpu: CPU to record in exit_info. Pass the stalled/hung CPU, not current.
  * @fmt: format string
  *
  * Called on system stall or lockup condition and initiates abort of sched_ext
@@ -5086,7 +4796,7 @@ bool scx_allow_ttwu_queue(const struct task_struct *p)
  * resolve the lockup. %false if sched_ext is not enabled or abort was already
  * initiated by someone else.
  */
-static __printf(1, 2) bool handle_lockup(const char *fmt, ...)
+static __printf(2, 3) bool handle_lockup(int exit_cpu, const char *fmt, ...)
 {
 	struct scx_sched *sch;
 	va_list args;
@@ -5102,7 +4812,7 @@ static __printf(1, 2) bool handle_lockup(const char *fmt, ...)
 	case SCX_ENABLING:
 	case SCX_ENABLED:
 		va_start(args, fmt);
-		ret = scx_verror(sch, fmt, args);
+		ret = scx_vexit(sch, SCX_EXIT_ERROR, 0, exit_cpu, fmt, args);
 		va_end(args);
 		return ret;
 	default:
@@ -5122,9 +4832,46 @@ static __printf(1, 2) bool handle_lockup(const char *fmt, ...)
  * resolve the reported RCU stall. %false if sched_ext is not enabled or someone
  * else already initiated abort.
  */
-bool scx_rcu_cpu_stall(void)
+bool scx_rcu_cpu_stall(const struct cpumask *stalled_mask)
 {
-	return handle_lockup("RCU CPU stall detected!");
+	struct scx_sched *sch;
+	struct scx_exit_info *ei;
+	int exit_cpu;
+
+	guard(rcu)();
+
+	sch = rcu_dereference(scx_root);
+	if (unlikely(!sch))
+		return false;
+
+	switch (scx_enable_state()) {
+	case SCX_ENABLING:
+	case SCX_ENABLED:
+		break;
+	default:
+		return false;
+	}
+
+	exit_cpu = cpumask_empty(stalled_mask) ? -1 : (int)cpumask_first(stalled_mask);
+	ei = sch->exit_info;
+
+	guard(preempt)();
+
+	if (!scx_claim_exit(sch, SCX_EXIT_ERROR))
+		return false;
+
+#ifdef CONFIG_STACKTRACE
+	ei->bt_len = stack_trace_save(ei->bt, SCX_EXIT_BT_LEN, 1);
+#endif
+	scnprintf(ei->msg, SCX_EXIT_MSG_LEN, "RCU CPU stall on CPUs (%*pbl)",
+		  cpumask_pr_args(stalled_mask));
+	ei->kind = SCX_EXIT_ERROR;
+	ei->reason = scx_exit_reason(SCX_EXIT_ERROR);
+	ei->exit_cpu = exit_cpu;
+	cpumask_copy(sch->stall_cpus, stalled_mask);
+
+	irq_work_queue(&sch->disable_irq_work);
+	return true;
 }
 
 /**
@@ -5139,11 +4886,13 @@ bool scx_rcu_cpu_stall(void)
  */
 void scx_softlockup(u32 dur_s)
 {
-	if (!handle_lockup("soft lockup - CPU %d stuck for %us", smp_processor_id(), dur_s))
+	int cpu = smp_processor_id();
+
+	if (!handle_lockup(cpu, "soft lockup - CPU %d stuck for %us", cpu, dur_s))
 		return;
 
 	printk_deferred(KERN_ERR "sched_ext: Soft lockup - CPU %d stuck for %us, disabling BPF scheduler\n",
-			smp_processor_id(), dur_s);
+			cpu, dur_s);
 }
 
 /*
@@ -5158,7 +4907,7 @@ static void scx_hardlockup_irq_workfn(struct irq_work *work)
 {
 	int cpu = atomic_xchg(&scx_hardlockup_cpu, -1);
 
-	if (cpu >= 0 && handle_lockup("hard lockup - CPU %d", cpu))
+	if (cpu >= 0 && handle_lockup(cpu, "hard lockup - CPU %d", cpu))
 		printk_deferred(KERN_ERR "sched_ext: Hard lockup - CPU %d, disabling BPF scheduler\n",
 				cpu);
 }
@@ -5194,7 +4943,7 @@ static u32 bypass_lb_cpu(struct scx_sched *sch, s32 donor,
 			 u32 nr_donor_target, u32 nr_donee_target)
 {
 	struct rq *donor_rq = cpu_rq(donor);
-	struct scx_dispatch_q *donor_dsq = bypass_dsq(sch, donor);
+	struct scx_dispatch_q *donor_dsq = scx_bypass_dsq(sch, donor);
 	struct task_struct *p, *n;
 	struct scx_dsq_list_node cursor = INIT_DSQ_LIST_CURSOR(cursor, donor_dsq, 0);
 	s32 delta = READ_ONCE(donor_dsq->nr) - nr_donor_target;
@@ -5242,7 +4991,7 @@ resume:
 		if (donee >= nr_cpu_ids)
 			continue;
 
-		donee_dsq = bypass_dsq(sch, donee);
+		donee_dsq = scx_bypass_dsq(sch, donee);
 
 		/*
 		 * $p's rq is not locked but $p's DSQ lock protects its
@@ -5263,7 +5012,7 @@ resume:
 		 * between bypass DSQs.
 		 */
 		dispatch_dequeue_locked(p, donor_dsq);
-		dispatch_enqueue(sch, cpu_rq(donee), donee_dsq, p, SCX_ENQ_NESTED);
+		scx_dispatch_enqueue(sch, cpu_rq(donee), donee_dsq, p, SCX_ENQ_NESTED);
 
 		/*
 		 * $donee might have been idle and need to be woken up. No need
@@ -5306,7 +5055,7 @@ static void bypass_lb_node(struct scx_sched *sch, int node)
 
 	/* count the target tasks and CPUs */
 	for_each_cpu_and(cpu, cpu_online_mask, node_mask) {
-		u32 nr = READ_ONCE(bypass_dsq(sch, cpu)->nr);
+		u32 nr = READ_ONCE(scx_bypass_dsq(sch, cpu)->nr);
 
 		nr_tasks += nr;
 		nr_cpus++;
@@ -5328,7 +5077,7 @@ static void bypass_lb_node(struct scx_sched *sch, int node)
 
 	cpumask_clear(donee_mask);
 	for_each_cpu_and(cpu, cpu_online_mask, node_mask) {
-		if (READ_ONCE(bypass_dsq(sch, cpu)->nr) < nr_target)
+		if (READ_ONCE(scx_bypass_dsq(sch, cpu)->nr) < nr_target)
 			cpumask_set_cpu(cpu, donee_mask);
 	}
 
@@ -5339,7 +5088,7 @@ static void bypass_lb_node(struct scx_sched *sch, int node)
 			break;
 		if (cpumask_test_cpu(cpu, donee_mask))
 			continue;
-		if (READ_ONCE(bypass_dsq(sch, cpu)->nr) <= nr_donor_target)
+		if (READ_ONCE(scx_bypass_dsq(sch, cpu)->nr) <= nr_donor_target)
 			continue;
 
 		nr_balanced += bypass_lb_cpu(sch, cpu, donee_mask, resched_mask,
@@ -5350,7 +5099,7 @@ static void bypass_lb_node(struct scx_sched *sch, int node)
 		resched_cpu(cpu);
 
 	for_each_cpu_and(cpu, cpu_online_mask, node_mask) {
-		u32 nr = READ_ONCE(bypass_dsq(sch, cpu)->nr);
+		u32 nr = READ_ONCE(scx_bypass_dsq(sch, cpu)->nr);
 
 		after_min = min(nr, after_min);
 		after_max = max(nr, after_max);
@@ -5376,7 +5125,7 @@ static void scx_bypass_lb_timerfn(struct timer_list *timer)
 	int node;
 	u32 intv_us;
 
-	if (!bypass_dsp_enabled(sch))
+	if (!scx_bypass_dsp_enabled(sch))
 		return;
 
 	for_each_node_with_cpus(node)
@@ -5442,9 +5191,9 @@ static void enable_bypass_dsp(struct scx_sched *sch)
 	 * dispatch enabled while a descendant is bypassing, which is all that's
 	 * required.
 	 *
-	 * bypass_dsp_enabled() test is used to determine whether to enter the
-	 * bypass dispatch handling path from both bypassing and hosting scheds.
-	 * Bump enable depth on both @sch and bypass dispatch host.
+	 * scx_bypass_dsp_enabled() test is used to determine whether to enter
+	 * the bypass dispatch handling path from both bypassing and hosting
+	 * scheds. Bump enable depth on both @sch and bypass dispatch host.
 	 */
 	ret = atomic_inc_return(&sch->bypass_dsp_enable_depth);
 	WARN_ON_ONCE(ret <= 0);
@@ -5464,7 +5213,7 @@ static void enable_bypass_dsp(struct scx_sched *sch)
 }
 
 /* may be called without holding scx_bypass_lock */
-static void disable_bypass_dsp(struct scx_sched *sch)
+void scx_disable_bypass_dsp(struct scx_sched *sch)
 {
 	s32 ret;
 
@@ -5512,7 +5261,7 @@ static void disable_bypass_dsp(struct scx_sched *sch)
  *
  * - scx_prio_less() reverts to the default core_sched_at order.
  */
-static void scx_bypass(struct scx_sched *sch, bool bypass)
+void scx_bypass(struct scx_sched *sch, bool bypass)
 {
 	struct scx_sched *pos;
 	unsigned long flags;
@@ -5609,7 +5358,7 @@ static void scx_bypass(struct scx_sched *sch, bool bypass)
 
 	/* disarming must come after moving all tasks out of the bypass DSQs */
 	if (!bypass)
-		disable_bypass_dsp(sch);
+		scx_disable_bypass_dsp(sch);
 unlock:
 	raw_spin_unlock_irqrestore(&scx_bypass_lock, flags);
 }
@@ -5672,7 +5421,7 @@ static void free_kick_syncs(void)
 	int cpu;
 
 	for_each_possible_cpu(cpu) {
-		struct scx_kick_syncs **ksyncs = per_cpu_ptr(&scx_kick_syncs, cpu);
+		struct scx_kick_syncs __rcu **ksyncs = per_cpu_ptr(&scx_kick_syncs, cpu);
 		struct scx_kick_syncs *to_free;
 
 		to_free = rcu_replace_pointer(*ksyncs, NULL, true);
@@ -5701,7 +5450,7 @@ static void refresh_watchdog(void)
 		cancel_delayed_work_sync(&scx_watchdog_work);
 }
 
-static s32 scx_link_sched(struct scx_sched *sch)
+s32 scx_link_sched(struct scx_sched *sch)
 {
 	const char *err_msg = "";
 	s32 ret = 0;
@@ -5750,7 +5499,7 @@ static s32 scx_link_sched(struct scx_sched *sch)
 	return 0;
 }
 
-static void scx_unlink_sched(struct scx_sched *sch)
+void scx_unlink_sched(struct scx_sched *sch)
 {
 	scoped_guard(raw_spinlock_irq, &scx_sched_lock) {
 #ifdef CONFIG_EXT_SUB_SCHED
@@ -5771,13 +5520,13 @@ static void scx_unlink_sched(struct scx_sched *sch)
  * @sch. Once @sch becomes empty during disable, there's no point in dumping it.
  * This prevents calling dump ops on a dead sch.
  */
-static void scx_disable_dump(struct scx_sched *sch)
+void scx_disable_dump(struct scx_sched *sch)
 {
 	guard(raw_spinlock_irqsave)(&scx_dump_lock);
 	sch->dump_disabled = true;
 }
 
-static void scx_log_sched_disable(struct scx_sched *sch)
+void scx_log_sched_disable(struct scx_sched *sch)
 {
 	struct scx_exit_info *ei = sch->exit_info;
 	const char *type = scx_parent(sch) ? "sub-scheduler" : "scheduler";
@@ -5797,202 +5546,6 @@ static void scx_log_sched_disable(struct scx_sched *sch)
 	}
 }
 
-#ifdef CONFIG_EXT_SUB_SCHED
-static DECLARE_WAIT_QUEUE_HEAD(scx_unlink_waitq);
-
-static void drain_descendants(struct scx_sched *sch)
-{
-	/*
-	 * Child scheds that finished the critical part of disabling will take
-	 * themselves off @sch->children. Wait for it to drain. As propagation
-	 * is recursive, empty @sch->children means that all proper descendant
-	 * scheds reached unlinking stage.
-	 */
-	wait_event(scx_unlink_waitq, list_empty(&sch->children));
-}
-
-static void scx_fail_parent(struct scx_sched *sch,
-			    struct task_struct *failed, s32 fail_code)
-{
-	struct scx_sched *parent = scx_parent(sch);
-	struct scx_task_iter sti;
-	struct task_struct *p;
-
-	scx_error(parent, "ops.init_task() failed (%d) for %s[%d] while disabling a sub-scheduler",
-		  fail_code, failed->comm, failed->pid);
-
-	/*
-	 * Once $parent is bypassed, it's safe to put SCX_TASK_NONE tasks into
-	 * it. This may cause downstream failures on the BPF side but $parent is
-	 * dying anyway.
-	 */
-	scx_bypass(parent, true);
-
-	scx_task_iter_start(&sti, sch->cgrp);
-	while ((p = scx_task_iter_next_locked(&sti))) {
-		if (scx_task_on_sched(parent, p))
-			continue;
-
-		scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
-			scx_disable_and_exit_task(sch, p);
-			scx_set_task_sched(p, parent);
-		}
-	}
-	scx_task_iter_stop(&sti);
-}
-
-static void scx_sub_disable(struct scx_sched *sch)
-{
-	struct scx_sched *parent = scx_parent(sch);
-	struct scx_task_iter sti;
-	struct task_struct *p;
-	int ret;
-
-	/*
-	 * Guarantee forward progress and wait for descendants to be disabled.
-	 * To limit disruptions, $parent is not bypassed. Tasks are fully
-	 * prepped and then inserted back into $parent.
-	 */
-	scx_bypass(sch, true);
-	drain_descendants(sch);
-
-	/*
-	 * Here, every runnable task is guaranteed to make forward progress and
-	 * we can safely use blocking synchronization constructs. Actually
-	 * disable ops.
-	 */
-	mutex_lock(&scx_enable_mutex);
-	percpu_down_write(&scx_fork_rwsem);
-	scx_cgroup_lock();
-
-	set_cgroup_sched(sch_cgroup(sch), parent);
-
-	scx_task_iter_start(&sti, sch->cgrp);
-	while ((p = scx_task_iter_next_locked(&sti))) {
-		struct rq *rq;
-		struct rq_flags rf;
-
-		/* filter out duplicate visits */
-		if (scx_task_on_sched(parent, p))
-			continue;
-
-		/*
-		 * By the time control reaches here, all descendant schedulers
-		 * should already have been disabled.
-		 */
-		WARN_ON_ONCE(!scx_task_on_sched(sch, p));
-
-		/*
-		 * @p is pinned by the iter: css_task_iter_next() takes a
-		 * reference and holds it until the next iter_next() call, so
-		 * @p->usage is guaranteed > 0.
-		 */
-		get_task_struct(p);
-
-		scx_task_iter_unlock(&sti);
-
-		/*
-		 * $p is READY or ENABLED on @sch. Initialize for $parent,
-		 * disable and exit from @sch, and then switch over to $parent.
-		 *
-		 * If a task fails to initialize for $parent, the only available
-		 * action is disabling $parent too. While this allows disabling
-		 * of a child sched to cause the parent scheduler to fail, the
-		 * failure can only originate from ops.init_task() of the
-		 * parent. A child can't directly affect the parent through its
-		 * own failures.
-		 */
-		ret = __scx_init_task(parent, p, false);
-		if (ret) {
-			scx_fail_parent(sch, p, ret);
-			put_task_struct(p);
-			break;
-		}
-
-		rq = task_rq_lock(p, &rf);
-
-		if (scx_get_task_state(p) == SCX_TASK_DEAD) {
-			/*
-			 * sched_ext_dead() raced us between __scx_init_task()
-			 * and this rq lock and ran exit_task() on @sch (the
-			 * sched @p was on at that point), not on $parent.
-			 * $parent's just-completed init is owed an exit_task()
-			 * and we issue it here.
-			 */
-			scx_sub_init_cancel_task(parent, p);
-			task_rq_unlock(rq, p, &rf);
-			put_task_struct(p);
-			continue;
-		}
-
-		scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
-			/*
-			 * $p is initialized for $parent and still attached to
-			 * @sch. Disable and exit for @sch, switch over to
-			 * $parent, override the state to READY to account for
-			 * $p having already been initialized, and then enable.
-			 */
-			scx_disable_and_exit_task(sch, p);
-			scx_set_task_state(p, SCX_TASK_INIT_BEGIN);
-			scx_set_task_state(p, SCX_TASK_INIT);
-			scx_set_task_sched(p, parent);
-			scx_set_task_state(p, SCX_TASK_READY);
-			scx_enable_task(parent, p);
-		}
-
-		task_rq_unlock(rq, p, &rf);
-		put_task_struct(p);
-	}
-	scx_task_iter_stop(&sti);
-
-	scx_disable_dump(sch);
-
-	scx_cgroup_unlock();
-	percpu_up_write(&scx_fork_rwsem);
-
-	/*
-	 * All tasks are moved off of @sch but there may still be on-going
-	 * operations (e.g. ops.select_cpu()). Drain them by flushing RCU. Use
-	 * the expedited version as ancestors may be waiting in bypass mode.
-	 * Also, tell the parent that there is no need to keep running bypass
-	 * DSQs for us.
-	 */
-	synchronize_rcu_expedited();
-	disable_bypass_dsp(sch);
-
-	scx_unlink_sched(sch);
-
-	mutex_unlock(&scx_enable_mutex);
-
-	/*
-	 * @sch is now unlinked from the parent's children list. Notify and call
-	 * ops.sub_detach/exit(). Note that ops.sub_detach/exit() must be called
-	 * after unlinking and releasing all locks. See scx_claim_exit().
-	 */
-	wake_up_all(&scx_unlink_waitq);
-
-	if (parent->ops.sub_detach && sch->sub_attached) {
-		struct scx_sub_detach_args sub_detach_args = {
-			.ops = &sch->ops,
-			.cgroup_path = sch->cgrp_path,
-		};
-		SCX_CALL_OP(parent, sub_detach, NULL,
-			    &sub_detach_args);
-	}
-
-	scx_log_sched_disable(sch);
-
-	if (sch->ops.exit)
-		SCX_CALL_OP(sch, exit, NULL, sch->exit_info);
-	if (sch->sub_kset)
-		kobject_del(&sch->sub_kset->kobj);
-	kobject_del(&sch->kobj);
-}
-#else	/* CONFIG_EXT_SUB_SCHED */
-static inline void drain_descendants(struct scx_sched *sch) { }
-static inline void scx_sub_disable(struct scx_sched *sch) { }
-#endif	/* CONFIG_EXT_SUB_SCHED */
-
 static void scx_root_disable(struct scx_sched *sch)
 {
 	struct scx_task_iter sti;
@@ -6240,7 +5793,7 @@ static void scx_disable(struct scx_sched *sch, enum scx_exit_kind kind)
  * as a noop. Syncing the irq_work first is required to guarantee the
  * kthread work has been queued before waiting for it.
  */
-static void scx_flush_disable_work(struct scx_sched *sch)
+void scx_flush_disable_work(struct scx_sched *sch)
 {
 	int kind;
 
@@ -6569,14 +6122,23 @@ static void scx_dump_state(struct scx_sched *sch, struct scx_exit_info *ei,
 	dump_line(&s, "----------");
 
 	/*
-	 * Dump the exit CPU first so it isn't lost to dump truncation, then
-	 * walk the rest in order, skipping the one already dumped.
+	 * Dump stalled CPUs first so they aren't lost to dump truncation, then
+	 * walk the rest in order. Fall back to exit_cpu if no stall mask set.
 	 */
-	if (ei->exit_cpu >= 0)
-		scx_dump_cpu(sch, &s, &dctx, ei->exit_cpu, dump_all_tasks);
-	for_each_possible_cpu(cpu) {
-		if (cpu != ei->exit_cpu)
+	if (!cpumask_empty(sch->stall_cpus)) {
+		for_each_cpu(cpu, sch->stall_cpus)
 			scx_dump_cpu(sch, &s, &dctx, cpu, dump_all_tasks);
+		for_each_possible_cpu(cpu) {
+			if (!cpumask_test_cpu(cpu, sch->stall_cpus))
+				scx_dump_cpu(sch, &s, &dctx, cpu, dump_all_tasks);
+		}
+	} else {
+		if (ei->exit_cpu >= 0)
+			scx_dump_cpu(sch, &s, &dctx, ei->exit_cpu, dump_all_tasks);
+		for_each_possible_cpu(cpu) {
+			if (cpu != ei->exit_cpu)
+				scx_dump_cpu(sch, &s, &dctx, cpu, dump_all_tasks);
+		}
 	}
 
 	dump_newline(&s);
@@ -6584,19 +6146,9 @@ static void scx_dump_state(struct scx_sched *sch, struct scx_exit_info *ei,
 	dump_line(&s, "--------------");
 
 	scx_read_events(sch, &events);
-	scx_dump_event(s, &events, SCX_EV_SELECT_CPU_FALLBACK);
-	scx_dump_event(s, &events, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE);
-	scx_dump_event(s, &events, SCX_EV_DISPATCH_KEEP_LAST);
-	scx_dump_event(s, &events, SCX_EV_ENQ_SKIP_EXITING);
-	scx_dump_event(s, &events, SCX_EV_ENQ_SKIP_MIGRATION_DISABLED);
-	scx_dump_event(s, &events, SCX_EV_REENQ_IMMED);
-	scx_dump_event(s, &events, SCX_EV_REENQ_LOCAL_REPEAT);
-	scx_dump_event(s, &events, SCX_EV_REFILL_SLICE_DFL);
-	scx_dump_event(s, &events, SCX_EV_BYPASS_DURATION);
-	scx_dump_event(s, &events, SCX_EV_BYPASS_DISPATCH);
-	scx_dump_event(s, &events, SCX_EV_BYPASS_ACTIVATE);
-	scx_dump_event(s, &events, SCX_EV_INSERT_NOT_OWNED);
-	scx_dump_event(s, &events, SCX_EV_SUB_BYPASS_DISPATCH);
+#define SCX_EVENT(name)	scx_dump_event(s, &events, name)
+	SCX_EVENTS_LIST(SCX_EVENT);
+#undef SCX_EVENT
 
 	if (seq_buf_has_overflowed(&s) && dump_len >= sizeof(trunc_marker))
 		memcpy(ei->dump + dump_len - sizeof(trunc_marker),
@@ -6653,7 +6205,7 @@ static int alloc_kick_syncs(void)
 	 * can exceed percpu allocator limits on large machines.
 	 */
 	for_each_possible_cpu(cpu) {
-		struct scx_kick_syncs **ksyncs = per_cpu_ptr(&scx_kick_syncs, cpu);
+		struct scx_kick_syncs __rcu **ksyncs = per_cpu_ptr(&scx_kick_syncs, cpu);
 		struct scx_kick_syncs *new_ksyncs;
 
 		WARN_ON_ONCE(rcu_access_pointer(*ksyncs));
@@ -6696,30 +6248,12 @@ static struct scx_sched_pnode *alloc_pnode(struct scx_sched *sch, int node)
 }
 
 /*
- * scx_enable() is offloaded to a dedicated system-wide RT kthread to avoid
- * starvation. During the READY -> ENABLED task switching loop, the calling
- * thread's sched_class gets switched from fair to ext. As fair has higher
- * priority than ext, the calling thread can be indefinitely starved under
- * fair-class saturation, leading to a system hang.
- */
-struct scx_enable_cmd {
-	struct kthread_work	work;
-	union {
-		struct sched_ext_ops		*ops;
-		struct sched_ext_ops_cid	*ops_cid;
-	};
-	bool			is_cid_type;
-	struct bpf_map		*arena_map;	/* arena ref to transfer to sch */
-	int			ret;
-};
-
-/*
  * Allocate and initialize a new scx_sched. @cgrp's reference is always
  * consumed whether the function succeeds or fails.
  */
-static struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
-						 struct cgroup *cgrp,
-						 struct scx_sched *parent)
+struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
+					  struct cgroup *cgrp,
+					  struct scx_sched *parent)
 {
 	struct sched_ext_ops *ops = cmd->ops;
 	struct scx_sched *sch;
@@ -6766,7 +6300,7 @@ static struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
 	}
 
 	for_each_possible_cpu(cpu) {
-		ret = init_dsq(bypass_dsq(sch, cpu), SCX_DSQ_BYPASS, sch);
+		ret = init_dsq(scx_bypass_dsq(sch, cpu), SCX_DSQ_BYPASS, sch);
 		if (ret) {
 			bypass_fail_cpu = cpu;
 			goto err_free_pcpu;
@@ -6813,6 +6347,10 @@ static struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
 		ret = -ENOMEM;
 		goto err_free_lb_cpumask;
 	}
+	if (!zalloc_cpumask_var(&sch->stall_cpus, GFP_KERNEL)) {
+		ret = -ENOMEM;
+		goto err_free_lb_resched_cpumask;
+	}
 	/*
 	 * Copy ops through the right union view. For cid-form the source is
 	 * struct sched_ext_ops_cid which lacks the trailing cpu_acquire/
@@ -6848,12 +6386,19 @@ static struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
 	INIT_LIST_HEAD(&sch->children);
 	INIT_LIST_HEAD(&sch->sibling);
 
-	if (parent)
+	if (parent) {
+		/*
+		 * Pin @parent for @sch's lifetime. The kobject hierarchy pins
+		 * it only via @parent->sub_kset, which is dropped during
+		 * disable. Released in scx_sched_free_rcu_work().
+		 */
+		kobject_get(&parent->kobj);
 		ret = kobject_init_and_add(&sch->kobj, &scx_ktype,
 					   &parent->sub_kset->kobj,
 					   "sub-%llu", cgroup_id(cgrp));
-	else
+	} else {
 		ret = kobject_init_and_add(&sch->kobj, &scx_ktype, NULL, "root");
+	}
 
 	if (ret < 0) {
 		RCU_INIT_POINTER(ops->priv, NULL);
@@ -6896,8 +6441,10 @@ static struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
 #ifdef CONFIG_EXT_SUB_SCHED
 err_free_lb_resched:
 	RCU_INIT_POINTER(ops->priv, NULL);
-	free_cpumask_var(sch->bypass_lb_resched_cpumask);
+	free_cpumask_var(sch->stall_cpus);
 #endif
+err_free_lb_resched_cpumask:
+	free_cpumask_var(sch->bypass_lb_resched_cpumask);
 err_free_lb_cpumask:
 	free_cpumask_var(sch->bypass_lb_donee_cpumask);
 err_stop_helper:
@@ -6906,7 +6453,7 @@ err_free_pcpu:
 	for_each_possible_cpu(cpu) {
 		if (cpu == bypass_fail_cpu)
 			break;
-		exit_dsq(bypass_dsq(sch, cpu));
+		exit_dsq(scx_bypass_dsq(sch, cpu));
 	}
 	free_percpu(sch->pcpu);
 err_free_pnode:
@@ -6950,7 +6497,7 @@ static int check_hotplug_seq(struct scx_sched *sch,
 	return 0;
 }
 
-static int validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops)
+int scx_validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops)
 {
 	/*
 	 * It doesn't make sense to specify the SCX_OPS_ENQ_LAST flag if the
@@ -6988,7 +6535,7 @@ static int validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops)
 	 * run past the BPF allocation. Skip for cid-form.
 	 */
 	if (!sch->is_cid_type && (ops->cpu_acquire || ops->cpu_release))
-		pr_warn("ops->cpu_acquire/release() are deprecated, use sched_switch TP instead\n");
+		pr_warn_ratelimited("ops->cpu_acquire/release() are deprecated, use sched_switch TP instead\n");
 
 	/*
 	 * Sub-scheduler support is tied to the cid-form struct_ops. A sub-sched
@@ -7113,7 +6660,7 @@ static void scx_root_enable_workfn(struct kthread_work *work)
 	if (sch->ops.init) {
 		ret = SCX_CALL_OP_RET(sch, init, NULL);
 		if (ret) {
-			ret = ops_sanitize_err(sch, "init", ret);
+			ret = scx_ops_sanitize_err(sch, "init", ret);
 			cpus_read_unlock();
 			scx_error(sch, "ops.init() failed (%d)", ret);
 			goto err_disable;
@@ -7146,7 +6693,7 @@ static void scx_root_enable_workfn(struct kthread_work *work)
 
 	cpus_read_unlock();
 
-	ret = validate_ops(sch, ops);
+	ret = scx_validate_ops(sch, ops);
 	if (ret)
 		goto err_disable;
 
@@ -7388,347 +6935,6 @@ err_disable:
 	cmd->ret = 0;
 }
 
-#ifdef CONFIG_EXT_SUB_SCHED
-/* verify that a scheduler can be attached to @cgrp and return the parent */
-static struct scx_sched *find_parent_sched(struct cgroup *cgrp)
-{
-	struct scx_sched *parent = cgrp->scx_sched;
-	struct scx_sched *pos;
-
-	lockdep_assert_held(&scx_sched_lock);
-
-	/* can't attach twice to the same cgroup */
-	if (parent->cgrp == cgrp)
-		return ERR_PTR(-EBUSY);
-
-	/* does $parent allow sub-scheds? */
-	if (!parent->ops.sub_attach)
-		return ERR_PTR(-EOPNOTSUPP);
-
-	/* can't insert between $parent and its exiting children */
-	list_for_each_entry(pos, &parent->children, sibling)
-		if (cgroup_is_descendant(pos->cgrp, cgrp))
-			return ERR_PTR(-EBUSY);
-
-	return parent;
-}
-
-static bool assert_task_ready_or_enabled(struct task_struct *p)
-{
-	u32 state = scx_get_task_state(p);
-
-	switch (state) {
-	case SCX_TASK_READY:
-	case SCX_TASK_ENABLED:
-		return true;
-	default:
-		WARN_ONCE(true, "sched_ext: Invalid task state %d for %s[%d] during enabling sub sched",
-			  state, p->comm, p->pid);
-		return false;
-	}
-}
-
-static void scx_sub_enable_workfn(struct kthread_work *work)
-{
-	struct scx_enable_cmd *cmd = container_of(work, struct scx_enable_cmd, work);
-	struct sched_ext_ops *ops = cmd->ops;
-	struct cgroup *cgrp;
-	struct scx_sched *parent, *sch;
-	struct scx_task_iter sti;
-	struct task_struct *p;
-	s32 i, ret;
-
-	mutex_lock(&scx_enable_mutex);
-
-	if (!scx_enabled()) {
-		ret = -ENODEV;
-		goto out_unlock;
-	}
-
-	/* See scx_root_enable_workfn() for the @ops->priv check. */
-	if (rcu_access_pointer(ops->priv)) {
-		ret = -EBUSY;
-		goto out_unlock;
-	}
-
-	cgrp = cgroup_get_from_id(ops->sub_cgroup_id);
-	if (IS_ERR(cgrp)) {
-		ret = PTR_ERR(cgrp);
-		goto out_unlock;
-	}
-
-	raw_spin_lock_irq(&scx_sched_lock);
-	parent = find_parent_sched(cgrp);
-	if (IS_ERR(parent)) {
-		raw_spin_unlock_irq(&scx_sched_lock);
-		ret = PTR_ERR(parent);
-		goto out_put_cgrp;
-	}
-	kobject_get(&parent->kobj);
-	raw_spin_unlock_irq(&scx_sched_lock);
-
-	/* scx_alloc_and_add_sched() consumes @cgrp whether it succeeds or not */
-	sch = scx_alloc_and_add_sched(cmd, cgrp, parent);
-	kobject_put(&parent->kobj);
-	if (IS_ERR(sch)) {
-		ret = PTR_ERR(sch);
-		goto out_unlock;
-	}
-
-	ret = scx_link_sched(sch);
-	if (ret)
-		goto err_disable;
-
-	if (sch->level >= SCX_SUB_MAX_DEPTH) {
-		scx_error(sch, "max nesting depth %d violated",
-			  SCX_SUB_MAX_DEPTH);
-		goto err_disable;
-	}
-
-	if (sch->ops.init) {
-		ret = SCX_CALL_OP_RET(sch, init, NULL);
-		if (ret) {
-			ret = ops_sanitize_err(sch, "init", ret);
-			scx_error(sch, "ops.init() failed (%d)", ret);
-			goto err_disable;
-		}
-		sch->exit_info->flags |= SCX_EFLAG_INITIALIZED;
-	}
-
-	ret = scx_arena_pool_init(sch);
-	if (ret)
-		goto err_disable;
-
-	ret = scx_set_cmask_scratch_alloc(sch);
-	if (ret)
-		goto err_disable;
-
-	if (validate_ops(sch, ops))
-		goto err_disable;
-
-	struct scx_sub_attach_args sub_attach_args = {
-		.ops = &sch->ops,
-		.cgroup_path = sch->cgrp_path,
-	};
-
-	ret = SCX_CALL_OP_RET(parent, sub_attach, NULL,
-			      &sub_attach_args);
-	if (ret) {
-		ret = ops_sanitize_err(sch, "sub_attach", ret);
-		scx_error(sch, "parent rejected (%d)", ret);
-		goto err_disable;
-	}
-	sch->sub_attached = true;
-
-	scx_bypass(sch, true);
-
-	for (i = SCX_OPI_BEGIN; i < SCX_OPI_END; i++)
-		if (((void (**)(void))ops)[i])
-			set_bit(i, sch->has_op);
-
-	percpu_down_write(&scx_fork_rwsem);
-	scx_cgroup_lock();
-
-	/*
-	 * Set cgroup->scx_sched's and check CSS_ONLINE. Either we see
-	 * !CSS_ONLINE or scx_cgroup_lifetime_notify() sees and shoots us down.
-	 */
-	set_cgroup_sched(sch_cgroup(sch), sch);
-	if (!(cgrp->self.flags & CSS_ONLINE)) {
-		scx_error(sch, "cgroup is not online");
-		goto err_unlock_and_disable;
-	}
-
-	/*
-	 * Initialize tasks for the new child $sch without exiting them for
-	 * $parent so that the tasks can always be reverted back to $parent
-	 * sched on child init failure.
-	 */
-	WARN_ON_ONCE(scx_enabling_sub_sched);
-	scx_enabling_sub_sched = sch;
-
-	scx_task_iter_start(&sti, sch->cgrp);
-	while ((p = scx_task_iter_next_locked(&sti))) {
-		struct rq *rq;
-		struct rq_flags rf;
-
-		/*
-		 * Task iteration may visit the same task twice when racing
-		 * against exiting. Use %SCX_TASK_SUB_INIT to mark tasks which
-		 * finished __scx_init_task() and skip if set.
-		 *
-		 * A task may exit and get freed between __scx_init_task()
-		 * completion and scx_enable_task(). In such cases,
-		 * scx_disable_and_exit_task() must exit the task for both the
-		 * parent and child scheds.
-		 */
-		if (p->scx.flags & SCX_TASK_SUB_INIT)
-			continue;
-
-		/* @p is pinned by the iter; see scx_sub_disable() */
-		get_task_struct(p);
-
-		if (!assert_task_ready_or_enabled(p)) {
-			ret = -EINVAL;
-			goto abort;
-		}
-
-		scx_task_iter_unlock(&sti);
-
-		/*
-		 * As $p is still on $parent, it can't be transitioned to INIT.
-		 * Let's worry about task state later. Use __scx_init_task().
-		 */
-		ret = __scx_init_task(sch, p, false);
-		if (ret)
-			goto abort;
-
-		rq = task_rq_lock(p, &rf);
-
-		if (scx_get_task_state(p) == SCX_TASK_DEAD) {
-			/*
-			 * sched_ext_dead() raced us between __scx_init_task()
-			 * and this rq lock and ran exit_task() on $parent (the
-			 * sched @p was on at that point), not on @sch. @sch's
-			 * just-completed init is owed an exit_task() and we
-			 * issue it here.
-			 */
-			scx_sub_init_cancel_task(sch, p);
-			task_rq_unlock(rq, p, &rf);
-			put_task_struct(p);
-			continue;
-		}
-
-		p->scx.flags |= SCX_TASK_SUB_INIT;
-		task_rq_unlock(rq, p, &rf);
-
-		put_task_struct(p);
-	}
-	scx_task_iter_stop(&sti);
-
-	/*
-	 * All tasks are prepped. Disable/exit tasks for $parent and enable for
-	 * the new @sch.
-	 */
-	scx_task_iter_start(&sti, sch->cgrp);
-	while ((p = scx_task_iter_next_locked(&sti))) {
-		/*
-		 * Use clearing of %SCX_TASK_SUB_INIT to detect and skip
-		 * duplicate iterations.
-		 */
-		if (!(p->scx.flags & SCX_TASK_SUB_INIT))
-			continue;
-
-		scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
-			/*
-			 * $p must be either READY or ENABLED. If ENABLED,
-			 * __scx_disabled_and_exit_task() first disables and
-			 * makes it READY. However, after exiting $p, it will
-			 * leave $p as READY.
-			 */
-			assert_task_ready_or_enabled(p);
-			__scx_disable_and_exit_task(parent, p);
-
-			/*
-			 * $p is now only initialized for @sch and READY, which
-			 * is what we want. Assign it to @sch and enable.
-			 */
-			scx_set_task_sched(p, sch);
-			scx_enable_task(sch, p);
-
-			p->scx.flags &= ~SCX_TASK_SUB_INIT;
-		}
-	}
-	scx_task_iter_stop(&sti);
-
-	scx_enabling_sub_sched = NULL;
-
-	scx_cgroup_unlock();
-	percpu_up_write(&scx_fork_rwsem);
-
-	scx_bypass(sch, false);
-
-	pr_info("sched_ext: BPF sub-scheduler \"%s\" enabled\n", sch->ops.name);
-	kobject_uevent(&sch->kobj, KOBJ_ADD);
-	ret = 0;
-	goto out_unlock;
-
-out_put_cgrp:
-	cgroup_put(cgrp);
-out_unlock:
-	mutex_unlock(&scx_enable_mutex);
-	cmd->ret = ret;
-	return;
-
-abort:
-	put_task_struct(p);
-	scx_task_iter_stop(&sti);
-
-	/*
-	 * Undo __scx_init_task() for tasks we marked. scx_enable_task() never
-	 * ran for @sch on them, so calling scx_disable_task() here would invoke
-	 * ops.disable() without a matching ops.enable(). scx_enabling_sub_sched
-	 * must stay set until SUB_INIT is cleared from every marked task -
-	 * scx_disable_and_exit_task() reads it when a task exits concurrently.
-	 */
-	scx_task_iter_start(&sti, sch->cgrp);
-	while ((p = scx_task_iter_next_locked(&sti))) {
-		if (p->scx.flags & SCX_TASK_SUB_INIT) {
-			scx_sub_init_cancel_task(sch, p);
-			p->scx.flags &= ~SCX_TASK_SUB_INIT;
-		}
-	}
-	scx_task_iter_stop(&sti);
-	scx_enabling_sub_sched = NULL;
-err_unlock_and_disable:
-	/* we'll soon enter disable path, keep bypass on */
-	scx_cgroup_unlock();
-	percpu_up_write(&scx_fork_rwsem);
-err_disable:
-	mutex_unlock(&scx_enable_mutex);
-	scx_flush_disable_work(sch);
-	cmd->ret = 0;
-}
-
-static s32 scx_cgroup_lifetime_notify(struct notifier_block *nb,
-				      unsigned long action, void *data)
-{
-	struct cgroup *cgrp = data;
-	struct cgroup *parent = cgroup_parent(cgrp);
-
-	if (!cgroup_on_dfl(cgrp))
-		return NOTIFY_OK;
-
-	switch (action) {
-	case CGROUP_LIFETIME_ONLINE:
-		/* inherit ->scx_sched from $parent */
-		if (parent)
-			rcu_assign_pointer(cgrp->scx_sched, parent->scx_sched);
-		break;
-	case CGROUP_LIFETIME_OFFLINE:
-		/* if there is a sched attached, shoot it down */
-		if (cgrp->scx_sched && cgrp->scx_sched->cgrp == cgrp)
-			scx_exit(cgrp->scx_sched, SCX_EXIT_UNREG_KERN,
-				 SCX_ECODE_RSN_CGROUP_OFFLINE,
-				 "cgroup %llu going offline", cgroup_id(cgrp));
-		break;
-	}
-
-	return NOTIFY_OK;
-}
-
-static struct notifier_block scx_cgroup_lifetime_nb = {
-	.notifier_call = scx_cgroup_lifetime_notify,
-};
-
-static s32 __init scx_cgroup_lifetime_notifier_init(void)
-{
-	return blocking_notifier_chain_register(&cgroup_lifetime_notifier,
-						&scx_cgroup_lifetime_nb);
-}
-core_initcall(scx_cgroup_lifetime_notifier_init);
-#endif	/* CONFIG_EXT_SUB_SCHED */
-
 static s32 scx_enable(struct scx_enable_cmd *cmd, struct bpf_link *link)
 {
 	static struct kthread_worker *helper;
@@ -7806,7 +7012,7 @@ static int bpf_scx_btf_struct_access(struct bpf_verifier_log *log,
 		     off + size <= offsetofend(struct task_struct, scx.slice)) ||
 		    (off >= offsetof(struct task_struct, scx.dsq_vtime) &&
 		     off + size <= offsetofend(struct task_struct, scx.dsq_vtime))) {
-			pr_warn("sched_ext: Writing directly to p->scx.slice/dsq_vtime is deprecated, use scx_bpf_task_set_slice/dsq_vtime()");
+			pr_warn_ratelimited("sched_ext: Writing directly to p->scx.slice/dsq_vtime is deprecated, use scx_bpf_task_set_slice/dsq_vtime()\n");
 			return SCALAR_VALUE;
 		}
 
@@ -7875,20 +7081,6 @@ static int bpf_scx_init_member(const struct btf_type *t,
 	return 0;
 }
 
-#ifdef CONFIG_EXT_SUB_SCHED
-static void scx_pstack_recursion_on_dispatch(struct bpf_prog *prog)
-{
-	struct scx_sched *sch;
-
-	guard(rcu)();
-	sch = scx_prog_sched(prog->aux);
-	if (unlikely(!sch))
-		return;
-
-	scx_error(sch, "dispatch recursion detected");
-}
-#endif	/* CONFIG_EXT_SUB_SCHED */
-
 static int bpf_scx_check_member(const struct btf_type *t,
 				const struct btf_member *member,
 				const struct bpf_prog *prog)
@@ -8773,7 +7965,7 @@ static bool scx_dsq_move(struct bpf_iter_scx_dsq_kern *kit,
 
 	/*
 	 * If the BPF scheduler keeps calling this function repeatedly, it can
-	 * cause similar live-lock conditions as consume_dispatch_q().
+	 * cause similar live-lock conditions as scx_consume_dispatch_q().
 	 */
 	if (unlikely(READ_ONCE(sch->aborting)))
 		return false;
@@ -8934,7 +8126,7 @@ __bpf_kfunc bool scx_bpf_dsq_move_to_local___v2(u64 dsq_id, u64 enq_flags,
 
 	dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx;
 
-	flush_dispatch_buf(sch, dspc->rq);
+	scx_flush_dispatch_buf(sch, dspc->rq);
 
 	dsq = find_user_dsq(sch, dsq_id);
 	if (unlikely(!dsq)) {
@@ -8942,7 +8134,7 @@ __bpf_kfunc bool scx_bpf_dsq_move_to_local___v2(u64 dsq_id, u64 enq_flags,
 		return false;
 	}
 
-	if (consume_dispatch_q(sch, dspc->rq, dsq, enq_flags)) {
+	if (scx_consume_dispatch_q(sch, dspc->rq, dsq, enq_flags)) {
 		/*
 		 * A successfully consumed task can be dequeued before it starts
 		 * running while the CPU is trying to migrate other dispatched
@@ -9059,45 +8251,6 @@ __bpf_kfunc bool scx_bpf_dsq_move_vtime(struct bpf_iter_scx_dsq *it__iter,
 			    p, dsq_id, enq_flags | SCX_ENQ_DSQ_PRIQ);
 }
 
-#ifdef CONFIG_EXT_SUB_SCHED
-/**
- * scx_bpf_sub_dispatch - Trigger dispatching on a child scheduler
- * @cgroup_id: cgroup ID of the child scheduler to dispatch
- * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs
- *
- * Allows a parent scheduler to trigger dispatching on one of its direct
- * child schedulers. The child scheduler runs its dispatch operation to
- * move tasks from dispatch queues to the local runqueue.
- *
- * Returns: true on success, false if cgroup_id is invalid, not a direct
- * child, or caller lacks dispatch permission.
- */
-__bpf_kfunc bool scx_bpf_sub_dispatch(u64 cgroup_id, const struct bpf_prog_aux *aux)
-{
-	struct rq *this_rq = this_rq();
-	struct scx_sched *parent, *child;
-
-	guard(rcu)();
-	parent = scx_prog_sched(aux);
-	if (unlikely(!parent))
-		return false;
-
-	child = scx_find_sub_sched(cgroup_id);
-
-	if (unlikely(!child))
-		return false;
-
-	if (unlikely(scx_parent(child) != parent)) {
-		scx_error(parent, "trying to dispatch a distant sub-sched on cgroup %llu",
-			  cgroup_id);
-		return false;
-	}
-
-	return scx_dispatch_sched(child, this_rq, this_rq->scx.sub_dispatch_prev,
-				  true);
-}
-#endif	/* CONFIG_EXT_SUB_SCHED */
-
 __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(scx_kfunc_ids_dispatch)
@@ -9285,7 +8438,7 @@ __bpf_kfunc bool scx_bpf_task_set_dsq_vtime(struct task_struct *p, u64 vtime,
 	return true;
 }
 
-static void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags)
+void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags)
 {
 	struct rq *this_rq;
 	unsigned long irq_flags;
@@ -10095,34 +9248,6 @@ __bpf_kfunc s32 scx_bpf_task_cid(const struct task_struct *p)
 }
 
 /**
- * scx_bpf_cpu_rq - Fetch the rq of a CPU
- * @cpu: CPU of the rq
- * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs
- */
-__bpf_kfunc struct rq *scx_bpf_cpu_rq(s32 cpu, const struct bpf_prog_aux *aux)
-{
-	struct scx_sched *sch;
-
-	guard(rcu)();
-
-	sch = scx_prog_sched(aux);
-	if (unlikely(!sch))
-		return NULL;
-
-	if (!scx_cpu_valid(sch, cpu, NULL))
-		return NULL;
-
-	if (!sch->warned_deprecated_rq) {
-		printk_deferred(KERN_WARNING "sched_ext: %s() is deprecated; "
-				"use scx_bpf_locked_rq() when holding rq lock "
-				"or scx_bpf_cpu_curr() to read remote curr safely.\n", __func__);
-		sch->warned_deprecated_rq = true;
-	}
-
-	return cpu_rq(cpu);
-}
-
-/**
  * scx_bpf_locked_rq - Return the rq currently locked by SCX
  * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs
  *
@@ -10288,26 +9413,15 @@ __bpf_kfunc u64 scx_bpf_now(void)
 
 static void scx_read_events(struct scx_sched *sch, struct scx_event_stats *events)
 {
-	struct scx_event_stats *e_cpu;
 	int cpu;
 
 	/* Aggregate per-CPU event counters into @events. */
 	memset(events, 0, sizeof(*events));
 	for_each_possible_cpu(cpu) {
-		e_cpu = &per_cpu_ptr(sch->pcpu, cpu)->event_stats;
-		scx_agg_event(events, e_cpu, SCX_EV_SELECT_CPU_FALLBACK);
-		scx_agg_event(events, e_cpu, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE);
-		scx_agg_event(events, e_cpu, SCX_EV_DISPATCH_KEEP_LAST);
-		scx_agg_event(events, e_cpu, SCX_EV_ENQ_SKIP_EXITING);
-		scx_agg_event(events, e_cpu, SCX_EV_ENQ_SKIP_MIGRATION_DISABLED);
-		scx_agg_event(events, e_cpu, SCX_EV_REENQ_IMMED);
-		scx_agg_event(events, e_cpu, SCX_EV_REENQ_LOCAL_REPEAT);
-		scx_agg_event(events, e_cpu, SCX_EV_REFILL_SLICE_DFL);
-		scx_agg_event(events, e_cpu, SCX_EV_BYPASS_DURATION);
-		scx_agg_event(events, e_cpu, SCX_EV_BYPASS_DISPATCH);
-		scx_agg_event(events, e_cpu, SCX_EV_BYPASS_ACTIVATE);
-		scx_agg_event(events, e_cpu, SCX_EV_INSERT_NOT_OWNED);
-		scx_agg_event(events, e_cpu, SCX_EV_SUB_BYPASS_DISPATCH);
+		struct scx_event_stats *e_cpu = &per_cpu_ptr(sch->pcpu, cpu)->event_stats;
+#define SCX_EVENT(name)	(events->name += READ_ONCE(e_cpu->name))
+		SCX_EVENTS_LIST(SCX_EVENT);
+#undef SCX_EVENT
 	}
 }
 
@@ -10412,7 +9526,6 @@ BTF_ID_FLAGS(func, scx_bpf_put_cpumask, KF_RELEASE)
 BTF_ID_FLAGS(func, scx_bpf_task_running, KF_RCU)
 BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU)
 BTF_ID_FLAGS(func, scx_bpf_task_cid, KF_RCU)
-BTF_ID_FLAGS(func, scx_bpf_cpu_rq, KF_IMPLICIT_ARGS)
 BTF_ID_FLAGS(func, scx_bpf_locked_rq, KF_IMPLICIT_ARGS | KF_RET_NULL)
 BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED)
 BTF_ID_FLAGS(func, scx_bpf_cid_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED)
@@ -10447,7 +9560,6 @@ static const struct btf_kfunc_id_set scx_kfunc_set_any = {
 BTF_KFUNCS_START(scx_kfunc_ids_cpu_only)
 BTF_ID_FLAGS(func, scx_bpf_kick_cpu, KF_IMPLICIT_ARGS)
 BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU)
-BTF_ID_FLAGS(func, scx_bpf_cpu_rq, KF_IMPLICIT_ARGS)
 BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED)
 BTF_ID_FLAGS(func, scx_bpf_cpu_node, KF_IMPLICIT_ARGS)
 BTF_ID_FLAGS(func, scx_bpf_cpuperf_cap, KF_IMPLICIT_ARGS)
@@ -10667,7 +9779,7 @@ static int __init scx_init(void)
 	/* @priv tail must align since both share the same data block */
 	CID_OFFSET_MATCH(priv, priv);
 	/*
-	 * cid-form must end exactly at @priv - validate_ops() skips
+	 * cid-form must end exactly at @priv - scx_validate_ops() skips
 	 * cpu_acquire/cpu_release for cid-form because reading those fields
 	 * past the BPF allocation would be UB.
 	 */
diff --git a/kernel/sched/ext/internal.h b/kernel/sched/ext/internal.h
index 145272cb4d8a..f9fe7c6ebc4b 100644
--- a/kernel/sched/ext/internal.h
+++ b/kernel/sched/ext/internal.h
@@ -11,6 +11,34 @@
 #include "../sched.h"
 #include "types.h"
 
+#include <trace/events/sched_ext.h>
+
+/**
+ * scx_add_event - Increase an event counter for 'name' by 'cnt'
+ * @sch: scx_sched to account events for
+ * @name: an event name defined in struct scx_event_stats
+ * @cnt: the number of the event occurred
+ *
+ * This can be used when preemption is not disabled.
+ */
+#define scx_add_event(sch, name, cnt) do {					\
+	this_cpu_add((sch)->pcpu->event_stats.name, (cnt));			\
+	trace_sched_ext_event(#name, (cnt));					\
+} while(0)
+
+/**
+ * __scx_add_event - Increase an event counter for 'name' by 'cnt'
+ * @sch: scx_sched to account events for
+ * @name: an event name defined in struct scx_event_stats
+ * @cnt: the number of the event occurred
+ *
+ * This should be used only when preemption is disabled.
+ */
+#define __scx_add_event(sch, name, cnt) do {					\
+	__this_cpu_add((sch)->pcpu->event_stats.name, (cnt));			\
+	trace_sched_ext_event(#name, cnt);					\
+} while(0)
+
 #define SCX_OP_IDX(op)		(offsetof(struct sched_ext_ops, op) / sizeof(void (*)(void)))
 #define SCX_MOFF_IDX(moff)	((moff) / sizeof(void (*)(void)))
 
@@ -1051,6 +1079,21 @@ struct scx_event_stats {
 	s64		SCX_EV_SUB_BYPASS_DISPATCH;
 };
 
+#define SCX_EVENTS_LIST(SCX_EVENT)					\
+	SCX_EVENT(SCX_EV_SELECT_CPU_FALLBACK);				\
+	SCX_EVENT(SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE);			\
+	SCX_EVENT(SCX_EV_DISPATCH_KEEP_LAST);				\
+	SCX_EVENT(SCX_EV_ENQ_SKIP_EXITING);				\
+	SCX_EVENT(SCX_EV_ENQ_SKIP_MIGRATION_DISABLED);			\
+	SCX_EVENT(SCX_EV_REENQ_IMMED);					\
+	SCX_EVENT(SCX_EV_REENQ_LOCAL_REPEAT);				\
+	SCX_EVENT(SCX_EV_REFILL_SLICE_DFL);				\
+	SCX_EVENT(SCX_EV_BYPASS_DURATION);				\
+	SCX_EVENT(SCX_EV_BYPASS_DISPATCH);				\
+	SCX_EVENT(SCX_EV_BYPASS_ACTIVATE);				\
+	SCX_EVENT(SCX_EV_INSERT_NOT_OWNED);				\
+	SCX_EVENT(SCX_EV_SUB_BYPASS_DISPATCH)
+
 struct scx_sched;
 
 enum scx_sched_pcpu_flags {
@@ -1157,7 +1200,7 @@ struct scx_sched {
 	u64			bypass_timestamp;
 	s32			bypass_depth;
 
-	/* bypass dispatch path enable state, see bypass_dsp_enabled() */
+	/* bypass dispatch path enable state, see scx_bypass_dsp_enabled() */
 	unsigned long		bypass_dsp_claim;
 	atomic_t		bypass_dsp_enable_depth;
 
@@ -1171,7 +1214,6 @@ struct scx_sched {
 	 * but it doesn't really matter.
 	 */
 	bool			warned_zero_slice:1;
-	bool			warned_deprecated_rq:1;
 	bool			warned_unassoc_progs:1;
 
 	struct list_head	all;
@@ -1206,6 +1248,7 @@ struct scx_sched {
 	struct timer_list	bypass_lb_timer;
 	cpumask_var_t		bypass_lb_donee_cpumask;
 	cpumask_var_t		bypass_lb_resched_cpumask;
+	cpumask_var_t		stall_cpus;
 	struct rcu_work		rcu_work;
 
 	/* all ancestors including self */
@@ -1469,21 +1512,24 @@ static const char *scx_enable_state_str[] = {
  * The sched_ext core uses a "lock dancing" protocol coordinated by
  * p->scx.holding_cpu. When moving a task to a different rq:
  *
- *   1. Verify task can be moved (CPU affinity, migration_disabled, etc.)
- *   2. Set p->scx.holding_cpu to the current CPU
- *   3. Set task state to %SCX_OPSS_NONE; dequeue waits while DISPATCHING
+ *   1. Set p->scx.holding_cpu to the current CPU
+ *   2. Set task state to %SCX_OPSS_NONE; dequeue waits while DISPATCHING
  *      is set, so clearing DISPATCHING first prevents the circular wait
  *      (safe to lock the rq we need)
- *   4. Unlock the current CPU's rq
- *   5. Lock src_rq (where the task currently lives)
- *   6. Verify p->scx.holding_cpu == current CPU, if not, dequeue won the
+ *   3. Unlock the current CPU's rq
+ *   4. Lock src_rq (where the task currently lives)
+ *   5. Verify p->scx.holding_cpu == current CPU, if not, dequeue won the
  *      race (dequeue clears holding_cpu to -1 when it takes the task), in
  *      this case migration is aborted
- *   7. If src_rq == dst_rq: clear holding_cpu and enqueue directly
+ *   6. If src_rq == dst_rq: clear holding_cpu and enqueue directly
  *      into dst_rq's local DSQ (no lock swap needed)
- *   8. Otherwise: call move_remote_task_to_local_dsq(), which releases
- *      src_rq, locks dst_rq, and performs the deactivate/activate
- *      migration cycle (dst_rq is held on return)
+ *   7. Otherwise, verify under src_rq lock that the task can be moved to dst_rq
+ *      (CPU affinity, migration_disabled, etc.). If not, clear holding_cpu,
+ *      leave the task on src_rq, and enqueue it on the fallback DSQ.
+ *   8. Otherwise (i.e. if the task can be moved to dst_rq), call
+ *      move_remote_task_to_local_dsq(), which releases src_rq, locks dst_rq,
+ *      and performs the deactivate/activate migration cycle
+ *      (dst_rq is held on return)
  *   9. Unlock dst_rq and re-lock the current CPU's rq to restore
  *      the lock state expected by the caller
  *
@@ -1517,6 +1563,41 @@ enum scx_ops_state {
 #define SCX_OPSS_STATE_MASK	((1LU << SCX_OPSS_QSEQ_SHIFT) - 1)
 #define SCX_OPSS_QSEQ_MASK	(~SCX_OPSS_STATE_MASK)
 
+/*
+ * SCX task iterator.
+ */
+struct scx_task_iter {
+	struct sched_ext_entity		cursor;
+	struct task_struct		*locked_task;
+	struct rq			*rq;
+	struct rq_flags			rf;
+	u32				cnt;
+	bool				list_locked;
+#ifdef CONFIG_EXT_SUB_SCHED
+	struct cgroup			*cgrp;
+	struct cgroup_subsys_state	*css_pos;
+	struct css_task_iter		css_iter;
+#endif
+};
+
+/*
+ * scx_enable() is offloaded to a dedicated system-wide RT kthread to avoid
+ * starvation. During the READY -> ENABLED task switching loop, the calling
+ * thread's sched_class gets switched from fair to ext. As fair has higher
+ * priority than ext, the calling thread can be indefinitely starved under
+ * fair-class saturation, leading to a system hang.
+ */
+struct scx_enable_cmd {
+	struct kthread_work	work;
+	union {
+		struct sched_ext_ops		*ops;
+		struct sched_ext_ops_cid	*ops_cid;
+	};
+	bool			is_cid_type;
+	struct bpf_map		*arena_map;	/* arena ref to transfer to sch */
+	int			ret;
+};
+
 extern struct scx_sched __rcu *scx_root;
 DECLARE_PER_CPU(struct rq *, scx_locked_rq_state);
 
@@ -1537,12 +1618,112 @@ __printf(5, 0) bool scx_vexit(struct scx_sched *sch, enum scx_exit_kind kind,
 __printf(5, 6) bool __scx_exit(struct scx_sched *sch, enum scx_exit_kind kind,
 			       s64 exit_code, s32 exit_cpu, const char *fmt, ...);
 
+u32 scx_get_task_state(const struct task_struct *p);
+void scx_set_task_state(struct task_struct *p, u32 state);
+void scx_task_iter_start(struct scx_task_iter *iter, struct cgroup *cgrp);
+void scx_task_iter_unlock(struct scx_task_iter *iter);
+void scx_task_iter_stop(struct scx_task_iter *iter);
+struct task_struct *scx_task_iter_next_locked(struct scx_task_iter *iter);
+bool scx_consume_dispatch_q(struct scx_sched *sch, struct rq *rq,
+			    struct scx_dispatch_q *dsq, u64 enq_flags);
+bool scx_consume_global_dsq(struct scx_sched *sch, struct rq *rq);
+bool scx_rq_online(struct rq *rq);
+void scx_flush_dispatch_buf(struct scx_sched *sch, struct rq *rq);
+void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags);
+void schedule_dsq_reenq(struct scx_sched *sch, struct scx_dispatch_q *dsq,
+			u64 reenq_flags, struct rq *locked_rq);
+int __scx_init_task(struct scx_sched *sch, struct task_struct *p, bool fork);
+void scx_enable_task(struct scx_sched *sch, struct task_struct *p);
+void __scx_disable_and_exit_task(struct scx_sched *sch, struct task_struct *p);
+void scx_sub_init_cancel_task(struct scx_sched *sch, struct task_struct *p);
+void scx_disable_and_exit_task(struct scx_sched *sch, struct task_struct *p);
+#if defined(CONFIG_EXT_GROUP_SCHED) || defined(CONFIG_EXT_SUB_SCHED)
+void scx_cgroup_lock(void);
+void scx_cgroup_unlock(void);
+#endif
+s32 scx_set_cmask_scratch_alloc(struct scx_sched *sch);
+void scx_disable_bypass_dsp(struct scx_sched *sch);
+void scx_bypass(struct scx_sched *sch, bool bypass);
+s32 scx_link_sched(struct scx_sched *sch);
+void scx_unlink_sched(struct scx_sched *sch);
+void scx_disable_dump(struct scx_sched *sch);
+void scx_log_sched_disable(struct scx_sched *sch);
+void scx_flush_disable_work(struct scx_sched *sch);
+struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
+					  struct cgroup *cgrp,
+					  struct scx_sched *parent);
+int scx_validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops);
+
+extern raw_spinlock_t scx_sched_lock;
+extern struct mutex scx_enable_mutex;
+extern struct percpu_rw_semaphore scx_fork_rwsem;
+#ifdef CONFIG_EXT_SUB_SCHED
+extern const struct rhashtable_params scx_sched_hash_params;
+extern struct rhashtable scx_sched_hash;
+extern struct scx_sched *scx_enabling_sub_sched;
+#endif
+
 #define scx_exit(sch, kind, exit_code, fmt, args...)				\
 	__scx_exit(sch, kind, exit_code, raw_smp_processor_id(), fmt, ##args)
 #define scx_error(sch, fmt, args...)						\
 	scx_exit((sch), SCX_EXIT_ERROR, 0, fmt, ##args)
-#define scx_verror(sch, fmt, args)						\
-	scx_vexit((sch), SCX_EXIT_ERROR, 0, raw_smp_processor_id(), fmt, args)
+
+static inline struct scx_dispatch_q *scx_bypass_dsq(struct scx_sched *sch, s32 cpu)
+{
+	return &per_cpu_ptr(sch->pcpu, cpu)->bypass_dsq;
+}
+
+/**
+ * scx_bypass_dsp_enabled - Check if bypass dispatch path is enabled
+ * @sch: scheduler to check
+ *
+ * When a descendant scheduler enters bypass mode, bypassed tasks are scheduled
+ * by the nearest non-bypassing ancestor, or the root scheduler if all ancestors
+ * are bypassing. In the former case, the ancestor is not itself bypassing but
+ * its bypass DSQs will be populated with bypassed tasks from descendants. Thus,
+ * the ancestor's bypass dispatch path must be active even though its own
+ * bypass_depth remains zero.
+ *
+ * This function checks bypass_dsp_enable_depth which is managed separately from
+ * bypass_depth to enable this decoupling. See enable_bypass_dsp() and
+ * scx_disable_bypass_dsp().
+ */
+static inline bool scx_bypass_dsp_enabled(struct scx_sched *sch)
+{
+	return unlikely(atomic_read(&sch->bypass_dsp_enable_depth));
+}
+
+/**
+ * scx_ops_sanitize_err - Sanitize a -errno value
+ * @sch: scx_sched to error out on error
+ * @ops_name: operation to blame on failure
+ * @err: -errno value to sanitize
+ *
+ * Verify @err is a valid -errno. If not, trigger scx_error() and return
+ * -%EPROTO. This is necessary because returning a rogue -errno up the chain can
+ * cause misbehaviors. For an example, a large negative return from
+ * ops.init_task() triggers an oops when passed up the call chain because the
+ * value fails IS_ERR() test after being encoded with ERR_PTR() and then is
+ * handled as a pointer.
+ */
+static inline int scx_ops_sanitize_err(struct scx_sched *sch, const char *ops_name, s32 err)
+{
+	if (err < 0 && err >= -MAX_ERRNO)
+		return err;
+
+	scx_error(sch, "ops.%s() returned an invalid errno %d", ops_name, err);
+	return -EPROTO;
+}
+
+static inline void scx_schedule_reenq_local(struct rq *rq, u64 reenq_flags)
+{
+	struct scx_sched *root = rcu_dereference_sched(scx_root);
+
+	if (WARN_ON_ONCE(!root))
+		return;
+
+	schedule_dsq_reenq(root, &rq->scx.local_dsq, reenq_flags, rq);
+}
 
 /*
  * Return the rq currently locked from an scx callback, or NULL if no rq is
diff --git a/kernel/sched/ext/sub.c b/kernel/sched/ext/sub.c
new file mode 100644
index 000000000000..050420427273
--- /dev/null
+++ b/kernel/sched/ext/sub.c
@@ -0,0 +1,668 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst
+ *
+ * Sub-scheduler hierarchy support.
+ *
+ * A sub-scheduler is an scx_sched attached to a cgroup subtree under another
+ * scx_sched. This file holds the sub-scheduler implementation: the scheduler
+ * tree walk, capability delegation, per-shard cap state and its sync, and the
+ * sub-scheduler enable/disable paths. The core dispatch/enqueue machinery it
+ * builds on lives in ext.c.
+ *
+ * Copyright (c) 2026 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2026 Tejun Heo <tj@kernel.org>
+ */
+#include <linux/rhashtable.h>
+#include "internal.h"
+#include "cid.h"
+#include "arena.h"
+#include "sub.h"
+
+#ifdef CONFIG_EXT_SUB_SCHED
+
+/**
+ * scx_next_descendant_pre - find the next descendant for pre-order walk
+ * @pos: the current position (%NULL to initiate traversal)
+ * @root: sched whose descendants to walk
+ *
+ * To be used by scx_for_each_descendant_pre(). Find the next descendant to
+ * visit for pre-order traversal of @root's descendants. @root is included in
+ * the iteration and the first node to be visited.
+ */
+struct scx_sched *scx_next_descendant_pre(struct scx_sched *pos, struct scx_sched *root)
+{
+	struct scx_sched *next;
+
+	lockdep_assert(lockdep_is_held(&scx_enable_mutex) ||
+		       lockdep_is_held(&scx_sched_lock));
+
+	/* if first iteration, visit @root */
+	if (!pos)
+		return root;
+
+	/* visit the first child if exists */
+	next = list_first_entry_or_null(&pos->children, struct scx_sched, sibling);
+	if (next)
+		return next;
+
+	/* no child, visit my or the closest ancestor's next sibling */
+	while (pos != root) {
+		if (!list_is_last(&pos->sibling, &scx_parent(pos)->children))
+			return list_next_entry(pos, sibling);
+		pos = scx_parent(pos);
+	}
+
+	return NULL;
+}
+
+static struct scx_sched *scx_find_sub_sched(u64 cgroup_id)
+{
+	return rhashtable_lookup(&scx_sched_hash, &cgroup_id,
+				 scx_sched_hash_params);
+}
+
+void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch)
+{
+	rcu_assign_pointer(p->scx.sched, sch);
+}
+
+struct cgroup *sch_cgroup(struct scx_sched *sch)
+{
+	return sch->cgrp;
+}
+
+/* for each descendant of @cgrp including self, set ->scx_sched to @sch */
+void set_cgroup_sched(struct cgroup *cgrp, struct scx_sched *sch)
+{
+	struct cgroup *pos;
+	struct cgroup_subsys_state *css;
+
+	cgroup_for_each_live_descendant_pre(pos, css, cgrp)
+		rcu_assign_pointer(pos->scx_sched, sch);
+}
+
+static DECLARE_WAIT_QUEUE_HEAD(scx_unlink_waitq);
+
+void drain_descendants(struct scx_sched *sch)
+{
+	/*
+	 * Child scheds that finished the critical part of disabling will take
+	 * themselves off @sch->children. Wait for it to drain. As propagation
+	 * is recursive, empty @sch->children means that all proper descendant
+	 * scheds reached unlinking stage.
+	 */
+	wait_event(scx_unlink_waitq, list_empty(&sch->children));
+}
+
+static void scx_fail_parent(struct scx_sched *sch,
+			    struct task_struct *failed, s32 fail_code)
+{
+	struct scx_sched *parent = scx_parent(sch);
+	struct scx_task_iter sti;
+	struct task_struct *p;
+
+	scx_error(parent, "ops.init_task() failed (%d) for %s[%d] while disabling a sub-scheduler",
+		  fail_code, failed->comm, failed->pid);
+
+	/*
+	 * Once $parent is bypassed, it's safe to put SCX_TASK_NONE tasks into
+	 * it. This may cause downstream failures on the BPF side but $parent is
+	 * dying anyway.
+	 */
+	scx_bypass(parent, true);
+
+	scx_task_iter_start(&sti, sch->cgrp);
+	while ((p = scx_task_iter_next_locked(&sti))) {
+		if (scx_task_on_sched(parent, p))
+			continue;
+
+		scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
+			scx_disable_and_exit_task(sch, p);
+			scx_set_task_sched(p, parent);
+		}
+	}
+	scx_task_iter_stop(&sti);
+}
+
+void scx_sub_disable(struct scx_sched *sch)
+{
+	struct scx_sched *parent = scx_parent(sch);
+	struct scx_task_iter sti;
+	struct task_struct *p;
+	int ret;
+
+	/*
+	 * Guarantee forward progress and wait for descendants to be disabled.
+	 * To limit disruptions, $parent is not bypassed. Tasks are fully
+	 * prepped and then inserted back into $parent.
+	 */
+	scx_bypass(sch, true);
+	drain_descendants(sch);
+
+	/*
+	 * Here, every runnable task is guaranteed to make forward progress and
+	 * we can safely use blocking synchronization constructs. Actually
+	 * disable ops.
+	 */
+	mutex_lock(&scx_enable_mutex);
+	percpu_down_write(&scx_fork_rwsem);
+	scx_cgroup_lock();
+
+	set_cgroup_sched(sch_cgroup(sch), parent);
+
+	scx_task_iter_start(&sti, sch->cgrp);
+	while ((p = scx_task_iter_next_locked(&sti))) {
+		struct rq *rq;
+		struct rq_flags rf;
+
+		/* filter out duplicate visits */
+		if (scx_task_on_sched(parent, p))
+			continue;
+
+		/*
+		 * By the time control reaches here, all descendant schedulers
+		 * should already have been disabled.
+		 */
+		WARN_ON_ONCE(!scx_task_on_sched(sch, p));
+
+		/*
+		 * @p is pinned by the iter: css_task_iter_next() takes a
+		 * reference and holds it until the next iter_next() call, so
+		 * @p->usage is guaranteed > 0.
+		 */
+		get_task_struct(p);
+
+		scx_task_iter_unlock(&sti);
+
+		/*
+		 * $p is READY or ENABLED on @sch. Initialize for $parent,
+		 * disable and exit from @sch, and then switch over to $parent.
+		 *
+		 * If a task fails to initialize for $parent, the only available
+		 * action is disabling $parent too. While this allows disabling
+		 * of a child sched to cause the parent scheduler to fail, the
+		 * failure can only originate from ops.init_task() of the
+		 * parent. A child can't directly affect the parent through its
+		 * own failures.
+		 */
+		ret = __scx_init_task(parent, p, false);
+		if (ret) {
+			scx_fail_parent(sch, p, ret);
+			put_task_struct(p);
+			break;
+		}
+
+		rq = task_rq_lock(p, &rf);
+
+		if (scx_get_task_state(p) == SCX_TASK_DEAD) {
+			/*
+			 * sched_ext_dead() raced us between __scx_init_task()
+			 * and this rq lock and ran exit_task() on @sch (the
+			 * sched @p was on at that point), not on $parent.
+			 * $parent's just-completed init is owed an exit_task()
+			 * and we issue it here.
+			 */
+			scx_sub_init_cancel_task(parent, p);
+			task_rq_unlock(rq, p, &rf);
+			put_task_struct(p);
+			continue;
+		}
+
+		scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
+			/*
+			 * $p is initialized for $parent and still attached to
+			 * @sch. Disable and exit for @sch, switch over to
+			 * $parent, override the state to READY to account for
+			 * $p having already been initialized, and then enable.
+			 */
+			scx_disable_and_exit_task(sch, p);
+			scx_set_task_state(p, SCX_TASK_INIT_BEGIN);
+			scx_set_task_state(p, SCX_TASK_INIT);
+			scx_set_task_sched(p, parent);
+			scx_set_task_state(p, SCX_TASK_READY);
+			scx_enable_task(parent, p);
+		}
+
+		task_rq_unlock(rq, p, &rf);
+		put_task_struct(p);
+	}
+	scx_task_iter_stop(&sti);
+
+	scx_disable_dump(sch);
+
+	scx_cgroup_unlock();
+	percpu_up_write(&scx_fork_rwsem);
+
+	/*
+	 * All tasks are moved off of @sch but there may still be on-going
+	 * operations (e.g. ops.select_cpu()). Drain them by flushing RCU. Use
+	 * the expedited version as ancestors may be waiting in bypass mode.
+	 * Also, tell the parent that there is no need to keep running bypass
+	 * DSQs for us.
+	 */
+	synchronize_rcu_expedited();
+	scx_disable_bypass_dsp(sch);
+
+	scx_unlink_sched(sch);
+
+	mutex_unlock(&scx_enable_mutex);
+
+	/*
+	 * @sch is now unlinked from the parent's children list. Notify and call
+	 * ops.sub_detach/exit(). Note that ops.sub_detach/exit() must be called
+	 * after unlinking and releasing all locks. See scx_claim_exit().
+	 */
+	wake_up_all(&scx_unlink_waitq);
+
+	if (parent->ops.sub_detach && sch->sub_attached) {
+		struct scx_sub_detach_args sub_detach_args = {
+			.ops = &sch->ops,
+			.cgroup_path = sch->cgrp_path,
+		};
+		SCX_CALL_OP(parent, sub_detach, NULL,
+			    &sub_detach_args);
+	}
+
+	scx_log_sched_disable(sch);
+
+	if (sch->ops.exit)
+		SCX_CALL_OP(sch, exit, NULL, sch->exit_info);
+	if (sch->sub_kset)
+		kobject_del(&sch->sub_kset->kobj);
+	kobject_del(&sch->kobj);
+}
+
+/* verify that a scheduler can be attached to @cgrp and return the parent */
+static struct scx_sched *find_parent_sched(struct cgroup *cgrp)
+{
+	struct scx_sched *parent = cgrp->scx_sched;
+	struct scx_sched *pos;
+
+	lockdep_assert_held(&scx_sched_lock);
+
+	/* can't attach twice to the same cgroup */
+	if (parent->cgrp == cgrp)
+		return ERR_PTR(-EBUSY);
+
+	/* does $parent allow sub-scheds? */
+	if (!parent->ops.sub_attach)
+		return ERR_PTR(-EOPNOTSUPP);
+
+	/* can't insert between $parent and its exiting children */
+	list_for_each_entry(pos, &parent->children, sibling)
+		if (cgroup_is_descendant(pos->cgrp, cgrp))
+			return ERR_PTR(-EBUSY);
+
+	return parent;
+}
+
+static bool assert_task_ready_or_enabled(struct task_struct *p)
+{
+	u32 state = scx_get_task_state(p);
+
+	switch (state) {
+	case SCX_TASK_READY:
+	case SCX_TASK_ENABLED:
+		return true;
+	default:
+		WARN_ONCE(true, "sched_ext: Invalid task state %d for %s[%d] during enabling sub sched",
+			  state, p->comm, p->pid);
+		return false;
+	}
+}
+
+void scx_sub_enable_workfn(struct kthread_work *work)
+{
+	struct scx_enable_cmd *cmd = container_of(work, struct scx_enable_cmd, work);
+	struct sched_ext_ops *ops = cmd->ops;
+	struct cgroup *cgrp;
+	struct scx_sched *parent, *sch;
+	struct scx_task_iter sti;
+	struct task_struct *p;
+	s32 i, ret;
+
+	mutex_lock(&scx_enable_mutex);
+
+	if (!scx_enabled()) {
+		ret = -ENODEV;
+		goto out_unlock;
+	}
+
+	/* See scx_root_enable_workfn() for the @ops->priv check. */
+	if (rcu_access_pointer(ops->priv)) {
+		ret = -EBUSY;
+		goto out_unlock;
+	}
+
+	cgrp = cgroup_get_from_id(ops->sub_cgroup_id);
+	if (IS_ERR(cgrp)) {
+		ret = PTR_ERR(cgrp);
+		goto out_unlock;
+	}
+
+	raw_spin_lock_irq(&scx_sched_lock);
+	parent = find_parent_sched(cgrp);
+	if (IS_ERR(parent)) {
+		raw_spin_unlock_irq(&scx_sched_lock);
+		ret = PTR_ERR(parent);
+		goto out_put_cgrp;
+	}
+	kobject_get(&parent->kobj);
+	raw_spin_unlock_irq(&scx_sched_lock);
+
+	/* scx_alloc_and_add_sched() consumes @cgrp whether it succeeds or not */
+	sch = scx_alloc_and_add_sched(cmd, cgrp, parent);
+	kobject_put(&parent->kobj);
+	if (IS_ERR(sch)) {
+		ret = PTR_ERR(sch);
+		goto out_unlock;
+	}
+
+	ret = scx_link_sched(sch);
+	if (ret)
+		goto err_disable;
+
+	if (sch->level >= SCX_SUB_MAX_DEPTH) {
+		scx_error(sch, "max nesting depth %d violated",
+			  SCX_SUB_MAX_DEPTH);
+		goto err_disable;
+	}
+
+	if (sch->ops.init) {
+		ret = SCX_CALL_OP_RET(sch, init, NULL);
+		if (ret) {
+			ret = scx_ops_sanitize_err(sch, "init", ret);
+			scx_error(sch, "ops.init() failed (%d)", ret);
+			goto err_disable;
+		}
+		sch->exit_info->flags |= SCX_EFLAG_INITIALIZED;
+	}
+
+	ret = scx_arena_pool_init(sch);
+	if (ret)
+		goto err_disable;
+
+	ret = scx_set_cmask_scratch_alloc(sch);
+	if (ret)
+		goto err_disable;
+
+	if (scx_validate_ops(sch, ops))
+		goto err_disable;
+
+	struct scx_sub_attach_args sub_attach_args = {
+		.ops = &sch->ops,
+		.cgroup_path = sch->cgrp_path,
+	};
+
+	ret = SCX_CALL_OP_RET(parent, sub_attach, NULL,
+			      &sub_attach_args);
+	if (ret) {
+		ret = scx_ops_sanitize_err(sch, "sub_attach", ret);
+		scx_error(sch, "parent rejected (%d)", ret);
+		goto err_disable;
+	}
+	sch->sub_attached = true;
+
+	scx_bypass(sch, true);
+
+	for (i = SCX_OPI_BEGIN; i < SCX_OPI_END; i++)
+		if (((void (**)(void))ops)[i])
+			set_bit(i, sch->has_op);
+
+	percpu_down_write(&scx_fork_rwsem);
+	scx_cgroup_lock();
+
+	/*
+	 * Set cgroup->scx_sched's and check CSS_ONLINE. Either we see
+	 * !CSS_ONLINE or scx_cgroup_lifetime_notify() sees and shoots us down.
+	 */
+	set_cgroup_sched(sch_cgroup(sch), sch);
+	if (!(cgrp->self.flags & CSS_ONLINE)) {
+		scx_error(sch, "cgroup is not online");
+		goto err_unlock_and_disable;
+	}
+
+	/*
+	 * Initialize tasks for the new child $sch without exiting them for
+	 * $parent so that the tasks can always be reverted back to $parent
+	 * sched on child init failure.
+	 */
+	WARN_ON_ONCE(scx_enabling_sub_sched);
+	scx_enabling_sub_sched = sch;
+
+	scx_task_iter_start(&sti, sch->cgrp);
+	while ((p = scx_task_iter_next_locked(&sti))) {
+		struct rq *rq;
+		struct rq_flags rf;
+
+		/*
+		 * Task iteration may visit the same task twice when racing
+		 * against exiting. Use %SCX_TASK_SUB_INIT to mark tasks which
+		 * finished __scx_init_task() and skip if set.
+		 *
+		 * A task may exit and get freed between __scx_init_task()
+		 * completion and scx_enable_task(). In such cases,
+		 * scx_disable_and_exit_task() must exit the task for both the
+		 * parent and child scheds.
+		 */
+		if (p->scx.flags & SCX_TASK_SUB_INIT)
+			continue;
+
+		/* @p is pinned by the iter; see scx_sub_disable() */
+		get_task_struct(p);
+
+		if (!assert_task_ready_or_enabled(p)) {
+			ret = -EINVAL;
+			goto abort;
+		}
+
+		scx_task_iter_unlock(&sti);
+
+		/*
+		 * As $p is still on $parent, it can't be transitioned to INIT.
+		 * Let's worry about task state later. Use __scx_init_task().
+		 */
+		ret = __scx_init_task(sch, p, false);
+		if (ret)
+			goto abort;
+
+		rq = task_rq_lock(p, &rf);
+
+		if (scx_get_task_state(p) == SCX_TASK_DEAD) {
+			/*
+			 * sched_ext_dead() raced us between __scx_init_task()
+			 * and this rq lock and ran exit_task() on $parent (the
+			 * sched @p was on at that point), not on @sch. @sch's
+			 * just-completed init is owed an exit_task() and we
+			 * issue it here.
+			 */
+			scx_sub_init_cancel_task(sch, p);
+			task_rq_unlock(rq, p, &rf);
+			put_task_struct(p);
+			continue;
+		}
+
+		p->scx.flags |= SCX_TASK_SUB_INIT;
+		task_rq_unlock(rq, p, &rf);
+
+		put_task_struct(p);
+	}
+	scx_task_iter_stop(&sti);
+
+	/*
+	 * All tasks are prepped. Disable/exit tasks for $parent and enable for
+	 * the new @sch.
+	 */
+	scx_task_iter_start(&sti, sch->cgrp);
+	while ((p = scx_task_iter_next_locked(&sti))) {
+		/*
+		 * Use clearing of %SCX_TASK_SUB_INIT to detect and skip
+		 * duplicate iterations.
+		 */
+		if (!(p->scx.flags & SCX_TASK_SUB_INIT))
+			continue;
+
+		scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
+			/*
+			 * $p must be either READY or ENABLED. If ENABLED,
+			 * __scx_disabled_and_exit_task() first disables and
+			 * makes it READY. However, after exiting $p, it will
+			 * leave $p as READY.
+			 */
+			assert_task_ready_or_enabled(p);
+			__scx_disable_and_exit_task(parent, p);
+
+			/*
+			 * $p is now only initialized for @sch and READY, which
+			 * is what we want. Assign it to @sch and enable.
+			 */
+			scx_set_task_sched(p, sch);
+			scx_enable_task(sch, p);
+
+			p->scx.flags &= ~SCX_TASK_SUB_INIT;
+		}
+	}
+	scx_task_iter_stop(&sti);
+
+	scx_enabling_sub_sched = NULL;
+
+	scx_cgroup_unlock();
+	percpu_up_write(&scx_fork_rwsem);
+
+	scx_bypass(sch, false);
+
+	pr_info("sched_ext: BPF sub-scheduler \"%s\" enabled\n", sch->ops.name);
+	kobject_uevent(&sch->kobj, KOBJ_ADD);
+	ret = 0;
+	goto out_unlock;
+
+out_put_cgrp:
+	cgroup_put(cgrp);
+out_unlock:
+	mutex_unlock(&scx_enable_mutex);
+	cmd->ret = ret;
+	return;
+
+abort:
+	put_task_struct(p);
+	scx_task_iter_stop(&sti);
+
+	/*
+	 * Undo __scx_init_task() for tasks we marked. scx_enable_task() never
+	 * ran for @sch on them, so calling scx_disable_task() here would invoke
+	 * ops.disable() without a matching ops.enable(). scx_enabling_sub_sched
+	 * must stay set until SUB_INIT is cleared from every marked task -
+	 * scx_disable_and_exit_task() reads it when a task exits concurrently.
+	 */
+	scx_task_iter_start(&sti, sch->cgrp);
+	while ((p = scx_task_iter_next_locked(&sti))) {
+		if (p->scx.flags & SCX_TASK_SUB_INIT) {
+			scx_sub_init_cancel_task(sch, p);
+			p->scx.flags &= ~SCX_TASK_SUB_INIT;
+		}
+	}
+	scx_task_iter_stop(&sti);
+	scx_enabling_sub_sched = NULL;
+err_unlock_and_disable:
+	/* we'll soon enter disable path, keep bypass on */
+	scx_cgroup_unlock();
+	percpu_up_write(&scx_fork_rwsem);
+err_disable:
+	mutex_unlock(&scx_enable_mutex);
+	scx_flush_disable_work(sch);
+	cmd->ret = 0;
+}
+
+static s32 scx_cgroup_lifetime_notify(struct notifier_block *nb,
+				      unsigned long action, void *data)
+{
+	struct cgroup *cgrp = data;
+	struct cgroup *parent = cgroup_parent(cgrp);
+
+	if (!cgroup_on_dfl(cgrp))
+		return NOTIFY_OK;
+
+	switch (action) {
+	case CGROUP_LIFETIME_ONLINE:
+		/* inherit ->scx_sched from $parent */
+		if (parent)
+			rcu_assign_pointer(cgrp->scx_sched, parent->scx_sched);
+		break;
+	case CGROUP_LIFETIME_OFFLINE:
+		/* if there is a sched attached, shoot it down */
+		if (cgrp->scx_sched && cgrp->scx_sched->cgrp == cgrp)
+			scx_exit(cgrp->scx_sched, SCX_EXIT_UNREG_KERN,
+				 SCX_ECODE_RSN_CGROUP_OFFLINE,
+				 "cgroup %llu going offline", cgroup_id(cgrp));
+		break;
+	}
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block scx_cgroup_lifetime_nb = {
+	.notifier_call = scx_cgroup_lifetime_notify,
+};
+
+static s32 __init scx_cgroup_lifetime_notifier_init(void)
+{
+	return blocking_notifier_chain_register(&cgroup_lifetime_notifier,
+						&scx_cgroup_lifetime_nb);
+}
+core_initcall(scx_cgroup_lifetime_notifier_init);
+
+void scx_pstack_recursion_on_dispatch(struct bpf_prog *prog)
+{
+	struct scx_sched *sch;
+
+	guard(rcu)();
+	sch = scx_prog_sched(prog->aux);
+	if (unlikely(!sch))
+		return;
+
+	scx_error(sch, "dispatch recursion detected");
+}
+
+__bpf_kfunc_start_defs();
+
+/**
+ * scx_bpf_sub_dispatch - Trigger dispatching on a child scheduler
+ * @cgroup_id: cgroup ID of the child scheduler to dispatch
+ * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs
+ *
+ * Allows a parent scheduler to trigger dispatching on one of its direct
+ * child schedulers. The child scheduler runs its dispatch operation to
+ * move tasks from dispatch queues to the local runqueue.
+ *
+ * Returns: true on success, false if cgroup_id is invalid, not a direct
+ * child, or caller lacks dispatch permission.
+ */
+__bpf_kfunc bool scx_bpf_sub_dispatch(u64 cgroup_id, const struct bpf_prog_aux *aux)
+{
+	struct rq *this_rq = this_rq();
+	struct scx_sched *parent, *child;
+
+	guard(rcu)();
+	parent = scx_prog_sched(aux);
+	if (unlikely(!parent))
+		return false;
+
+	child = scx_find_sub_sched(cgroup_id);
+
+	if (unlikely(!child))
+		return false;
+
+	if (unlikely(scx_parent(child) != parent)) {
+		scx_error(parent, "trying to dispatch a distant sub-sched on cgroup %llu",
+			  cgroup_id);
+		return false;
+	}
+
+	return scx_dispatch_sched(child, this_rq, this_rq->scx.sub_dispatch_prev,
+				  true);
+}
+
+__bpf_kfunc_end_defs();
+
+#endif	/* CONFIG_EXT_SUB_SCHED */
diff --git a/kernel/sched/ext/sub.h b/kernel/sched/ext/sub.h
new file mode 100644
index 000000000000..460a9fd196dc
--- /dev/null
+++ b/kernel/sched/ext/sub.h
@@ -0,0 +1,161 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst
+ *
+ * Sub-scheduler hierarchy support.
+ *
+ * Copyright (c) 2026 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2026 Tejun Heo <tj@kernel.org>
+ */
+#ifndef _KERNEL_SCHED_EXT_SUB_H
+#define _KERNEL_SCHED_EXT_SUB_H
+
+#include "internal.h"
+#include "cid.h"
+
+#ifdef CONFIG_EXT_SUB_SCHED
+
+struct scx_sched *scx_next_descendant_pre(struct scx_sched *pos, struct scx_sched *root);
+void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch);
+struct cgroup *sch_cgroup(struct scx_sched *sch);
+void set_cgroup_sched(struct cgroup *cgrp, struct scx_sched *sch);
+void scx_pstack_recursion_on_dispatch(struct bpf_prog *prog);
+void drain_descendants(struct scx_sched *sch);
+void scx_sub_disable(struct scx_sched *sch);
+void scx_sub_enable_workfn(struct kthread_work *work);
+bool scx_bpf_sub_dispatch(u64 cgroup_id, const struct bpf_prog_aux *aux);
+
+#else	/* CONFIG_EXT_SUB_SCHED */
+
+static inline struct scx_sched *scx_next_descendant_pre(struct scx_sched *pos, struct scx_sched *root) { return pos ? NULL : root; }
+static inline void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch) {}
+static inline struct cgroup *sch_cgroup(struct scx_sched *sch) { return NULL; }
+static inline void set_cgroup_sched(struct cgroup *cgrp, struct scx_sched *sch) {}
+static inline void drain_descendants(struct scx_sched *sch) { }
+static inline void scx_sub_disable(struct scx_sched *sch) { }
+
+#endif	/* CONFIG_EXT_SUB_SCHED */
+
+/**
+ * scx_for_each_descendant_pre - pre-order walk of a sched's descendants
+ * @pos: iteration cursor
+ * @root: sched to walk the descendants of
+ *
+ * Walk @root's descendants. @root is included in the iteration and the first
+ * node to be visited. Must be called with either scx_enable_mutex or
+ * scx_sched_lock held.
+ */
+#define scx_for_each_descendant_pre(pos, root)					\
+	for ((pos) = scx_next_descendant_pre(NULL, (root)); (pos);		\
+	     (pos) = scx_next_descendant_pre((pos), (root)))
+
+/*
+ * One user of this function is scx_bpf_dispatch() which can be called
+ * recursively as sub-sched dispatches nest. Always inline to reduce stack usage
+ * from the call frame.
+ */
+static __always_inline bool
+scx_dispatch_sched(struct scx_sched *sch, struct rq *rq,
+		   struct task_struct *prev, bool nested)
+{
+	struct scx_dsp_ctx *dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx;
+	int nr_loops = SCX_DSP_MAX_LOOPS;
+	s32 cpu = cpu_of(rq);
+	bool prev_on_sch = (prev->sched_class == &ext_sched_class) &&
+		scx_task_on_sched(sch, prev);
+
+	if (scx_consume_global_dsq(sch, rq))
+		return true;
+
+	if (scx_bypass_dsp_enabled(sch)) {
+		/* if @sch is bypassing, only the bypass DSQs are active */
+		if (scx_bypassing(sch, cpu))
+			return scx_consume_dispatch_q(sch, rq, scx_bypass_dsq(sch, cpu), 0);
+
+#ifdef CONFIG_EXT_SUB_SCHED
+		/*
+		 * If @sch isn't bypassing but its children are, @sch is
+		 * responsible for making forward progress for both its own
+		 * tasks that aren't bypassing and the bypassing descendants'
+		 * tasks. The following implements a simple built-in behavior -
+		 * let each CPU try to run the bypass DSQ every Nth time.
+		 *
+		 * Later, if necessary, we can add an ops flag to suppress the
+		 * auto-consumption and a kfunc to consume the bypass DSQ and,
+		 * so that the BPF scheduler can fully control scheduling of
+		 * bypassed tasks.
+		 */
+		struct scx_sched_pcpu *pcpu = per_cpu_ptr(sch->pcpu, cpu);
+
+		if (!(pcpu->bypass_host_seq++ % SCX_BYPASS_HOST_NTH) &&
+		    scx_consume_dispatch_q(sch, rq, scx_bypass_dsq(sch, cpu), 0)) {
+			__scx_add_event(sch, SCX_EV_SUB_BYPASS_DISPATCH, 1);
+			return true;
+		}
+#endif	/* CONFIG_EXT_SUB_SCHED */
+	}
+
+	if (unlikely(!SCX_HAS_OP(sch, dispatch)) || !scx_rq_online(rq))
+		return false;
+
+	dspc->rq = rq;
+
+	/*
+	 * The dispatch loop. Because scx_flush_dispatch_buf() may drop the rq
+	 * lock, the local DSQ might still end up empty after a successful
+	 * ops.dispatch(). If the local DSQ is empty even after ops.dispatch()
+	 * produced some tasks, retry. The BPF scheduler may depend on this
+	 * looping behavior to simplify its implementation.
+	 */
+	do {
+		dspc->nr_tasks = 0;
+
+		if (nested) {
+			SCX_CALL_OP(sch, dispatch, rq, scx_cpu_arg(cpu),
+				    prev_on_sch ? prev : NULL);
+		} else {
+			/* stash @prev so that nested invocations can access it */
+			rq->scx.sub_dispatch_prev = prev;
+			SCX_CALL_OP(sch, dispatch, rq, scx_cpu_arg(cpu),
+				    prev_on_sch ? prev : NULL);
+			rq->scx.sub_dispatch_prev = NULL;
+		}
+
+		scx_flush_dispatch_buf(sch, rq);
+
+		if ((prev->scx.flags & SCX_TASK_QUEUED) && prev->scx.slice) {
+			rq->scx.flags |= SCX_RQ_BAL_KEEP;
+			return true;
+		}
+		if (rq->scx.local_dsq.nr)
+			return true;
+		if (scx_consume_global_dsq(sch, rq))
+			return true;
+
+		/*
+		 * ops.dispatch() can trap us in this loop by repeatedly
+		 * dispatching ineligible tasks. Break out once in a while to
+		 * allow the watchdog to run. As IRQ can't be enabled in
+		 * balance(), we want to complete this scheduling cycle and then
+		 * start a new one. IOW, we want to call resched_curr() on the
+		 * next, most likely idle, task, not the current one. Use
+		 * __scx_bpf_kick_cpu() for deferred kicking.
+		 */
+		if (unlikely(!--nr_loops)) {
+			scx_kick_cpu(sch, cpu, 0);
+			break;
+		}
+	} while (dspc->nr_tasks);
+
+	/*
+	 * Prevent the CPU from going idle while bypassed descendants have tasks
+	 * queued. Without this fallback, bypassed tasks could stall if the host
+	 * scheduler's ops.dispatch() doesn't yield any tasks.
+	 */
+	if (scx_bypass_dsp_enabled(sch))
+		return scx_consume_dispatch_q(sch, rq, scx_bypass_dsq(sch, cpu), 0);
+
+	return false;
+}
+
+#endif /* _KERNEL_SCHED_EXT_SUB_H */
diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h
index 9591a6e778ce..bd51986c4c42 100644
--- a/tools/sched_ext/include/scx/common.bpf.h
+++ b/tools/sched_ext/include/scx/common.bpf.h
@@ -96,7 +96,6 @@ s32 scx_bpf_pick_any_cpu_node(const cpumask_t *cpus_allowed, int node, u64 flags
 s32 scx_bpf_pick_any_cpu(const cpumask_t *cpus_allowed, u64 flags) __ksym;
 bool scx_bpf_task_running(const struct task_struct *p) __ksym;
 s32 scx_bpf_task_cpu(const struct task_struct *p) __ksym;
-struct rq *scx_bpf_cpu_rq(s32 cpu) __ksym;
 struct rq *scx_bpf_locked_rq(void) __ksym;
 struct task_struct *scx_bpf_cpu_curr(s32 cpu) __ksym __weak;
 struct task_struct *scx_bpf_tid_to_task(u64 tid) __ksym __weak;
@@ -983,8 +982,8 @@ extern struct irqtime___local cpu_irqtime __ksym __weak;
 static inline struct rq___local *get_current_rq(u32 cpu)
 {
 	/*
-	 * This is a workaround to get an rq pointer since we decided to
-	 * deprecate scx_bpf_cpu_rq().
+	 * This is a workaround to get an rq pointer now that
+	 * scx_bpf_cpu_rq() has been removed.
 	 *
 	 * WARNING: The caller must hold the rq lock for @cpu. This is
 	 * guaranteed when called from scheduling callbacks (ops.running,
diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h
index 87f15f296234..133058578668 100644
--- a/tools/sched_ext/include/scx/compat.bpf.h
+++ b/tools/sched_ext/include/scx/compat.bpf.h
@@ -234,23 +234,6 @@ static inline bool __COMPAT_is_enq_cpu_selected(u64 enq_flags)
 	 scx_bpf_pick_any_cpu(cpus_allowed, flags))
 
 /*
- * v6.18: Add a helper to retrieve the current task running on a CPU.
- *
- * Keep this helper available until v6.20 for compatibility.
- */
-static inline struct task_struct *__COMPAT_scx_bpf_cpu_curr(int cpu)
-{
-	struct rq *rq;
-
-	if (bpf_ksym_exists(scx_bpf_cpu_curr))
-		return scx_bpf_cpu_curr(cpu);
-
-	rq = scx_bpf_cpu_rq(cpu);
-
-	return rq ? rq->curr : NULL;
-}
-
-/*
  * v6.19: To work around BPF maximum parameter limit, the following kfuncs are
  * replaced with variants that pack scalar arguments in a struct. Wrappers are
  * provided to maintain source compatibility.
diff --git a/tools/sched_ext/include/scx/compat.h b/tools/sched_ext/include/scx/compat.h
index 602f07061ee3..23d9ef3e4c9d 100644
--- a/tools/sched_ext/include/scx/compat.h
+++ b/tools/sched_ext/include/scx/compat.h
@@ -28,7 +28,7 @@ static inline bool __COMPAT_read_enum(const char *type, const char *name, u64 *v
 	const struct btf_type *t;
 	const char *n;
 	s32 tid;
-	int i;
+	__u32 i;
 
 	__COMPAT_load_vmlinux_btf();
 
@@ -42,7 +42,7 @@ static inline bool __COMPAT_read_enum(const char *type, const char *name, u64 *v
 	if (btf_is_enum(t)) {
 		struct btf_enum *e = btf_enum(t);
 
-		for (i = 0; i < BTF_INFO_VLEN(t->info); i++) {
+		for (i = 0; i < btf_vlen(t); i++) {
 			n = btf__name_by_offset(__COMPAT_vmlinux_btf, e[i].name_off);
 			SCX_BUG_ON(!n, "btf__name_by_offset()");
 			if (!strcmp(n, name)) {
@@ -53,7 +53,7 @@ static inline bool __COMPAT_read_enum(const char *type, const char *name, u64 *v
 	} else if (btf_is_enum64(t)) {
 		struct btf_enum64 *e = btf_enum64(t);
 
-		for (i = 0; i < BTF_INFO_VLEN(t->info); i++) {
+		for (i = 0; i < btf_vlen(t); i++) {
 			n = btf__name_by_offset(__COMPAT_vmlinux_btf, e[i].name_off);
 			SCX_BUG_ON(!n, "btf__name_by_offset()");
 			if (!strcmp(n, name)) {
@@ -85,7 +85,7 @@ static inline bool __COMPAT_struct_has_field(const char *type, const char *field
 	const struct btf_member *m;
 	const char *n;
 	s32 tid;
-	int i;
+	__u32 i;
 
 	__COMPAT_load_vmlinux_btf();
 	tid = btf__find_by_name_kind(__COMPAT_vmlinux_btf, type, BTF_KIND_STRUCT);
@@ -97,7 +97,7 @@ static inline bool __COMPAT_struct_has_field(const char *type, const char *field
 
 	m = btf_members(t);
 
-	for (i = 0; i < BTF_INFO_VLEN(t->info); i++) {
+	for (i = 0; i < btf_vlen(t); i++) {
 		n = btf__name_by_offset(__COMPAT_vmlinux_btf, m[i].name_off);
 		SCX_BUG_ON(!n, "btf__name_by_offset()");
 			if (!strcmp(n, field))
diff --git a/tools/sched_ext/scx_cpu0.c b/tools/sched_ext/scx_cpu0.c
index 4966e3d4c724..84a47aee2f95 100644
--- a/tools/sched_ext/scx_cpu0.c
+++ b/tools/sched_ext/scx_cpu0.c
@@ -62,7 +62,7 @@ int main(int argc, char **argv)
 {
 	struct scx_cpu0 *skel;
 	struct bpf_link *link;
-	__u32 opt;
+	__s32 opt;
 	__u64 ecode;
 
 	libbpf_set_print(libbpf_print_fn);
diff --git a/tools/sched_ext/scx_flatcg.bpf.c b/tools/sched_ext/scx_flatcg.bpf.c
index fec359581826..0fd214cc61da 100644
--- a/tools/sched_ext/scx_flatcg.bpf.c
+++ b/tools/sched_ext/scx_flatcg.bpf.c
@@ -256,7 +256,7 @@ static void cgrp_cap_budget(struct cgv_node *cgv_node, struct fcg_cgrp_ctx *cgc)
 	 * and thus can't be updated and repositioned. Instead, we collect the
 	 * vtime deltas separately and apply it asynchronously here.
 	 */
-	delta = __sync_fetch_and_sub(&cgc->cvtime_delta, cgc->cvtime_delta);
+	delta = __sync_fetch_and_and(&cgc->cvtime_delta, 0);
 	cvtime = cgv_node->cvtime + delta;
 
 	/*
@@ -570,7 +570,8 @@ void BPF_STRUCT_OPS(fcg_stopping, struct task_struct *p, bool runnable)
 	cgc = find_cgrp_ctx(cgrp);
 	if (cgc) {
 		__sync_fetch_and_add(&cgc->cvtime_delta,
-				     p->se.sum_exec_runtime - taskc->bypassed_at);
+				     (p->se.sum_exec_runtime - taskc->bypassed_at) *
+				     FCG_HWEIGHT_ONE / (cgc->hweight ?: 1));
 		taskc->bypassed_at = 0;
 	}
 	bpf_cgroup_release(cgrp);
diff --git a/tools/sched_ext/scx_sdt.c b/tools/sched_ext/scx_sdt.c
index bf664b2d3785..ef197b266a36 100644
--- a/tools/sched_ext/scx_sdt.c
+++ b/tools/sched_ext/scx_sdt.c
@@ -44,7 +44,7 @@ int main(int argc, char **argv)
 {
 	struct scx_sdt *skel;
 	struct bpf_link *link;
-	__u32 opt;
+	__s32 opt;
 	__u64 ecode;
 
 	libbpf_set_print(libbpf_print_fn);
diff --git a/tools/sched_ext/scx_simple.c b/tools/sched_ext/scx_simple.c
index c3b48611712b..34f9785335b7 100644
--- a/tools/sched_ext/scx_simple.c
+++ b/tools/sched_ext/scx_simple.c
@@ -64,7 +64,7 @@ int main(int argc, char **argv)
 {
 	struct scx_simple *skel;
 	struct bpf_link *link;
-	__u32 opt;
+	__s32 opt;
 	__u64 ecode;
 
 	libbpf_set_print(libbpf_print_fn);
diff --git a/tools/sched_ext/scx_userland.c b/tools/sched_ext/scx_userland.c
index 616043c165e6..192b79c7e4aa 100644
--- a/tools/sched_ext/scx_userland.c
+++ b/tools/sched_ext/scx_userland.c
@@ -326,7 +326,7 @@ static int spawn_stats_thread(void)
 static void pre_bootstrap(int argc, char **argv)
 {
 	int err;
-	__u32 opt;
+	__s32 opt;
 	struct sched_param sched_param = {
 		.sched_priority = sched_get_priority_max(SCHED_EXT),
 	};