[PATCH 3/8] sched_ext: Relocate scx_cgroup_enabled

scx_cgroup_enabled is in the CONFIG_EXT_GROUP_SCHED block. The upcoming
cgroup migration re-homing needs the gate outside the block. Move the
definition and flag flips outside CONFIG_EXT_GROUP_SCHED. No functional
changes.

Signed-off-by: Tejun Heo <[email protected]>
---
 kernel/sched/ext/ext.c      | 18 ++++++++++++------
 kernel/sched/ext/internal.h |  1 +
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index 145bda57b6fe..cd99947b4229 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -80,6 +80,14 @@ static bool scx_switching_all;
 DEFINE_STATIC_KEY_FALSE(__scx_switched_all);
 static DEFINE_STATIC_KEY_FALSE(__scx_tid_to_task_enabled);
 
+/*
+ * Gates cgroup ops delivery. Set at the end of the cgroup init phase of root
+ * enable and cleared before root disable starts tearing down tasks, both under
+ * scx_cgroup_lock(). Holding cgroup_lock() and seeing %true guarantees no race
+ * against root tearing down tasks.
+ */
+bool scx_cgroup_enabled;
+
 /*
  * True once SCX_OPS_TID_TO_TASK has been negotiated with the root scheduler
  * and the tid->task table is live. Wraps the static key so callers don't
@@ -4309,7 +4317,6 @@ bool scx_can_stop_tick(struct rq *rq)
 #ifdef CONFIG_EXT_GROUP_SCHED
 
 DEFINE_STATIC_PERCPU_RWSEM(scx_cgroup_ops_rwsem);
-static bool scx_cgroup_enabled;
 
 void scx_tg_init(struct task_group *tg)
 {
@@ -4689,8 +4696,6 @@ static void scx_cgroup_exit(struct scx_sched *sch)
 {
 	struct cgroup_subsys_state *css;
 
-	scx_cgroup_enabled = false;
-
 	/*
 	 * scx_tg_on/offline() are excluded through cgroup_lock(). If we walk
 	 * cgroups and exit all the inited ones, all online cgroups are exited.
@@ -4745,9 +4750,6 @@ static int scx_cgroup_init(struct scx_sched *sch)
 		tg->scx.flags |= SCX_TG_INITED;
 	}
 
-	WARN_ON_ONCE(scx_cgroup_enabled);
-	scx_cgroup_enabled = true;
-
 	return 0;
 }
 
@@ -5971,6 +5973,7 @@ static void scx_root_disable(struct scx_sched *sch)
 	 * doesn't race against scx_disable_and_exit_task().
 	 */
 	scx_cgroup_lock();
+	scx_cgroup_enabled = false;
 	scx_cgroup_exit(sch);
 	scx_cgroup_unlock();
 
@@ -7234,6 +7237,9 @@ static void scx_root_enable_workfn(struct kthread_work *work)
 	if (ret)
 		goto err_disable_unlock_all;
 
+	WARN_ON_ONCE(scx_cgroup_enabled);
+	scx_cgroup_enabled = true;
+
 	scx_task_iter_start(&sti, NULL);
 	while ((p = scx_task_iter_next_locked(&sti))) {
 		/*
diff --git a/kernel/sched/ext/internal.h b/kernel/sched/ext/internal.h
index 4f4130f0d121..d76ac22019af 100644
--- a/kernel/sched/ext/internal.h
+++ b/kernel/sched/ext/internal.h
@@ -1949,6 +1949,7 @@ __printf(3, 0) s32 scx_bstr_format(struct scx_sched *sch, struct scx_bstr_buf *b
 extern raw_spinlock_t scx_sched_lock;
 extern struct mutex scx_enable_mutex;
 extern struct percpu_rw_semaphore scx_fork_rwsem;
+extern bool scx_cgroup_enabled;
 extern raw_spinlock_t scx_exit_bstr_buf_lock;
 extern struct scx_bstr_buf scx_exit_bstr_buf;
 #ifdef CONFIG_EXT_SUB_SCHED
-- 
2.55.0