Re: [PATCH] sched_ext: Fix build errors and unused label warning in non-cgroup configs

[Andrea Righi <arighi@nvidia.com>]

Hi Cheng-Yang,

On Sat, Mar 21, 2026 at 03:05:15PM +0800, Cheng-Yang Chou wrote:
> When building without CONFIG_EXT_GROUP_SCHED and CONFIG_EXT_SUB_SCHED,
> clang reports errors for undeclared cgroup_put() and cgroup_get() calls.
> It also flags an unused err_stop_helper label.
> 
> This conditionally compiles the cgroup reference counting functions and
> the error handling label to match the configurations that require them,
> preventing implicit declaration errors and unused label warnings.
> 
> Tested with both configs enabled/disabled.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202603210903.IrKhPd6k-lkp@intel.com/
> Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
> ---
>  kernel/sched/ext.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 94548ee9ad85..2e7a1259bd7c 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -6494,8 +6494,10 @@ static struct scx_sched *scx_alloc_and_add_sched(struct sched_ext_ops *ops,
>  #endif	/* CONFIG_EXT_SUB_SCHED */
>  	return sch;
>  
> +#ifdef CONFIG_EXT_SUB_SCHED
>  err_stop_helper:
>  	kthread_destroy_worker(sch->helper);
> +#endif

CONFIG_EXT_SUB_SCHED is always defined whenever ext.c compiles, so this one
is unnecessary.

>  err_free_pcpu:
>  	for_each_possible_cpu(cpu) {
>  		if (cpu == bypass_fail_cpu)
> @@ -6514,7 +6516,9 @@ 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)
>  	cgroup_put(cgrp);
> +#endif

This ifdef around cgroup_get()/cgroup_put() also always evaluates to true
because EXT_SUB_SCHED is always true regardless of EXT_GROUP_SCHED.

>  	return ERR_PTR(ret);
>  }
>  
> @@ -6603,7 +6607,9 @@ 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)
>  	cgroup_get(cgrp);
> +#endif

Ditto.

>  	sch = scx_alloc_and_add_sched(ops, cgrp, NULL);
>  	if (IS_ERR(sch)) {
>  		ret = PTR_ERR(sch);
> -- 

This looks like a false positive, the kernel test robot likely tested with
a manually crafted config, so I think we shouldn't apply this patch.

Thanks,
-Andrea