sched_ext: Align cgroup #ifdef guards with SUB_SCHED vs GROUP_SCHED

Two EXT_GROUP_SCHED/SUB_SCHED guards are misclassified:

- scx_root_enable_workfn()'s cgroup_get(cgrp) and the err_put_cgrp unwind
  in scx_alloc_and_add_sched() are under `#if GROUP || SUB`, but the
  matching cgroup_put() in scx_sched_free_rcu_work() is inside `#ifdef SUB`
  only (via sch->cgrp, stored only under SUB). GROUP-only would leak a
  reference on every root-sched enable.

- sch_cgroup() / set_cgroup_sched() live under `#if GROUP || SUB` but touch
  SUB-only fields (sch->cgrp, cgroup->scx_sched). GROUP-only wouldn't
  compile.

GROUP needs CGROUP_SCHED; SUB needs only CGROUPS. CGROUPS=y/CGROUP_SCHED=n
gives the reachable GROUP=n, SUB=y combination; GROUP=y, SUB=n isn't
reachable today (SUB is def_bool y under CGROUPS). Neither miscategorization
triggers a real bug in any reachable config, but keep the guards honest:

- Narrow cgroup_get and err_put_cgrp to `#ifdef SUB` (matches the free-side
  put).
- Move sch_cgroup() and set_cgroup_sched() to a separate `#ifdef SUB` block
  with no-op stubs for the !SUB case; keep root_cgroup() and scx_cgroup_{
  lock,unlock}() under `#if GROUP || SUB` since those only need cgroup core.

Fixes: ebeca1f930ea ("sched_ext: Introduce cgroup sub-sched support")
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index e07f8c46e399cd37d97ec141d6aa158645d94e81..e2898d60315b2bcecf1a3f7da6b14e3ad215abe2 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -4413,21 +4413,6 @@ static struct cgroup *root_cgroup(void)
        return &cgrp_dfl_root.cgrp;
 }
 
-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);
-}
-
 static void scx_cgroup_lock(void)
 {
 #ifdef CONFIG_EXT_GROUP_SCHED
@@ -4445,12 +4430,30 @@ static void scx_cgroup_unlock(void)
 }
 #else  /* CONFIG_EXT_GROUP_SCHED || CONFIG_EXT_SUB_SCHED */
 static struct cgroup *root_cgroup(void) { return NULL; }
-static struct cgroup *sch_cgroup(struct scx_sched *sch) { return NULL; }
-static void set_cgroup_sched(struct cgroup *cgrp, struct scx_sched *sch) {}
 static void scx_cgroup_lock(void) {}
 static 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 struct cgroup *sch_cgroup(struct scx_sched *sch) { return NULL; }
+static void set_cgroup_sched(struct cgroup *cgrp, struct scx_sched *sch) {}
+#endif /* CONFIG_EXT_SUB_SCHED */
+
 /*
  * Omitted operations:
  *
@@ -6604,7 +6607,7 @@ err_free_ei:
 err_free_sch:
        kfree(sch);
 err_put_cgrp:
-#if defined(CONFIG_EXT_GROUP_SCHED) || defined(CONFIG_EXT_SUB_SCHED)
+#ifdef CONFIG_EXT_SUB_SCHED
        cgroup_put(cgrp);
 #endif
        return ERR_PTR(ret);
@@ -6695,7 +6698,7 @@ static void scx_root_enable_workfn(struct kthread_work *work)
        if (ret)
                goto err_unlock;
 
-#if defined(CONFIG_EXT_GROUP_SCHED) || defined(CONFIG_EXT_SUB_SCHED)
+#ifdef CONFIG_EXT_SUB_SCHED
        cgroup_get(cgrp);
 #endif
        sch = scx_alloc_and_add_sched(ops, cgrp, NULL);