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sched_ext, sched/core: Don't call scx_group_set_weight() prematurely from sched_create_group()

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During task_group creation, sched_create_group() calls
scx_group_set_weight() with CGROUP_WEIGHT_DFL to initialize the sched_ext
portion. This is premature and ends up calling ops.cgroup_set_weight() with
an incorrect @cgrp before ops.cgroup_init() is called.

sched_create_group() should just initialize SCX related fields in the new
task_group. Fix it by factoring out scx_tg_init() from sched_init() and
making sched_create_group() call that function instead of
scx_group_set_weight().

v2: Retain CONFIG_EXT_GROUP_SCHED ifdef in sched_init() as removing it leads
    to build failures on !CONFIG_GROUP_SCHED configs.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 8195136669 ("sched_ext: Add cgroup support")
Cc: stable@vger.kernel.org # v6.12+
This commit is contained in:
Tejun Heo 2025-06-16 10:13:25 -10:00
parent c50784e99f
commit 33796b9187
3 changed files with 9 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

4
kernel/sched/core.c
View file

@ -8545,7 +8545,7 @@ void __init sched_init(void)
init_cfs_bandwidth(&root_task_group.cfs_bandwidth, NULL);
#endif /* CONFIG_FAIR_GROUP_SCHED */
#ifdef CONFIG_EXT_GROUP_SCHED
root_task_group.scx_weight = CGROUP_WEIGHT_DFL;
scx_tg_init(&root_task_group);
#endif /* CONFIG_EXT_GROUP_SCHED */
#ifdef CONFIG_RT_GROUP_SCHED
root_task_group.rt_se = (struct sched_rt_entity **)ptr;
@ -8985,7 +8985,7 @@ struct task_group *sched_create_group(struct task_group *parent)
if (!alloc_rt_sched_group(tg, parent))
goto err;
scx_group_set_weight(tg, CGROUP_WEIGHT_DFL);
scx_tg_init(tg);
alloc_uclamp_sched_group(tg, parent);
return tg;

5
kernel/sched/ext.c
View file

@ -4092,6 +4092,11 @@ bool scx_can_stop_tick(struct rq *rq)
DEFINE_STATIC_PERCPU_RWSEM(scx_cgroup_rwsem);
static bool scx_cgroup_enabled;
void scx_tg_init(struct task_group *tg)
{
tg->scx_weight = CGROUP_WEIGHT_DFL;
}
int scx_tg_online(struct task_group *tg)
{
struct scx_sched *sch = scx_root;

2
kernel/sched/ext.h
View file

@ -79,6 +79,7 @@ static inline void scx_update_idle(struct rq *rq, bool idle, bool do_notify) {}
#ifdef CONFIG_CGROUP_SCHED
#ifdef CONFIG_EXT_GROUP_SCHED
void scx_tg_init(struct task_group *tg);
int scx_tg_online(struct task_group *tg);
void scx_tg_offline(struct task_group *tg);
int scx_cgroup_can_attach(struct cgroup_taskset *tset);
@ -88,6 +89,7 @@ void scx_cgroup_cancel_attach(struct cgroup_taskset *tset);
void scx_group_set_weight(struct task_group *tg, unsigned long cgrp_weight);
void scx_group_set_idle(struct task_group *tg, bool idle);
#else /* CONFIG_EXT_GROUP_SCHED */
static inline void scx_tg_init(struct task_group *tg) {}
static inline int scx_tg_online(struct task_group *tg) { return 0; }
static inline void scx_tg_offline(struct task_group *tg) {}
static inline int scx_cgroup_can_attach(struct cgroup_taskset *tset) { return 0; }