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sched_ext: Align cgroup #ifdef guards with SUB_SCHED vs GROUP_SCHED

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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: ebeca1f930 ("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>
This commit is contained in:
Tejun Heo 2026-04-24 14:31:36 -10:00
parent d292aa00de
commit c0e8ddc76d
1 changed files with 22 additions and 19 deletions
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41
kernel/sched/ext.c
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@ -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 @@ static struct scx_sched *scx_alloc_and_add_sched(struct sched_ext_ops *ops,
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);