* Re: [PATCH] sched_ext: Fix build errors and unused label warning in non-cgroup configs
2026-03-21 19:10 ` [PATCH] sched_ext: Fix build errors and unused label warning in non-cgroup configs Tejun Heo
@ 2026-03-21 23:26 ` Andrea Righi
2026-03-22 6:43 ` Cheng-Yang Chou
1 sibling, 0 replies; 3+ messages in thread
From: Andrea Righi @ 2026-03-21 23:26 UTC (permalink / raw)
To: Tejun Heo
Cc: Cheng-Yang Chou, sched-ext, David Vernet, Changwoo Min,
Ching-Chun Huang, Chia-Ping Tsai, kernel test robot,
Emil Tsalapatis, linux-kernel
Hi,
On Sat, Mar 21, 2026 at 09:10:03AM -1000, Tejun Heo wrote:
> Hello,
>
> On Sat, Mar 21, 2026 at 03:35:20PM +0100, Andrea Righi wrote:
> > 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.
>
> It's not a false positive. CONFIG_SCHED_CLASS_EXT doesn't depend on
> CONFIG_CGROUPS in Kconfig, so SCHED_CLASS_EXT=y with CGROUPS=n is a
> valid config. I reproduced the build failure using the bot's config.
>
> The issue is that CONFIG_EXT_SUB_SCHED is def_bool y depending only on
> SCHED_CLASS_EXT, so it's always on. But EXT_SUB_SCHED fundamentally
> needs cgroups (cgroup_path, cgroup_get, cgroup_put, cgroup_id, etc.),
> so the missing dependency is there.
Ah you guys are right! I was assuming that you can't have
CONFIG_SCHED_CLASS_EXT=y and CONFIG_CGROUPS=n, but that's just wrong.
So ignore my comment and sorry for the noise.
>
> Cheng-Yang, can you send a v2 with the following approach?
>
> 1. Add CGROUPS dependency to EXT_SUB_SCHED in init/Kconfig:
>
> config EXT_SUB_SCHED
> def_bool y
> - depends on SCHED_CLASS_EXT
> + depends on SCHED_CLASS_EXT && CGROUPS
>
> 2. Guard err_stop_helper with #ifdef CONFIG_EXT_SUB_SCHED (only
> jumped to from within CONFIG_EXT_SUB_SCHED code):
>
> +#ifdef CONFIG_EXT_SUB_SCHED
> err_stop_helper:
> kthread_destroy_worker(sch->helper);
> +#endif
> err_free_pcpu:
>
> 3. Guard cgroup_get/cgroup_put in common paths with the existing
> CONFIG_EXT_GROUP_SCHED || CONFIG_EXT_SUB_SCHED pattern (matching
> the root_cgroup() / sch_cgroup() stubs):
>
> err_put_cgrp:
> +#if defined(CONFIG_EXT_GROUP_SCHED) || defined(CONFIG_EXT_SUB_SCHED)
> cgroup_put(cgrp);
> +#endif
>
> and:
>
> +#if defined(CONFIG_EXT_GROUP_SCHED) || defined(CONFIG_EXT_SUB_SCHED)
> cgroup_get(cgrp);
> +#endif
> sch = scx_alloc_and_add_sched(ops, cgrp, NULL);
>
> I verified this builds clean with both CGROUPS=y and CGROUPS=n.
And this looks good also on my side.
Thanks,
-Andrea
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] sched_ext: Fix build errors and unused label warning in non-cgroup configs
2026-03-21 19:10 ` [PATCH] sched_ext: Fix build errors and unused label warning in non-cgroup configs Tejun Heo
2026-03-21 23:26 ` Andrea Righi
@ 2026-03-22 6:43 ` Cheng-Yang Chou
1 sibling, 0 replies; 3+ messages in thread
From: Cheng-Yang Chou @ 2026-03-22 6:43 UTC (permalink / raw)
To: Tejun Heo
Cc: Andrea Righi, sched-ext, David Vernet, Changwoo Min,
Ching-Chun Huang, Chia-Ping Tsai, kernel test robot,
Emil Tsalapatis, linux-kernel
Hi Tejun,
On Sat, Mar 21, 2026 at 09:10:03AM -1000, Tejun Heo wrote:
> Hello,
>
> On Sat, Mar 21, 2026 at 03:35:20PM +0100, Andrea Righi wrote:
> > 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.
>
> It's not a false positive. CONFIG_SCHED_CLASS_EXT doesn't depend on
> CONFIG_CGROUPS in Kconfig, so SCHED_CLASS_EXT=y with CGROUPS=n is a
> valid config. I reproduced the build failure using the bot's config.
>
> The issue is that CONFIG_EXT_SUB_SCHED is def_bool y depending only on
> SCHED_CLASS_EXT, so it's always on. But EXT_SUB_SCHED fundamentally
> needs cgroups (cgroup_path, cgroup_get, cgroup_put, cgroup_id, etc.),
> so the missing dependency is there.
>
> Cheng-Yang, can you send a v2 with the following approach?
>
> 1. Add CGROUPS dependency to EXT_SUB_SCHED in init/Kconfig:
>
> config EXT_SUB_SCHED
> def_bool y
> - depends on SCHED_CLASS_EXT
> + depends on SCHED_CLASS_EXT && CGROUPS
>
> 2. Guard err_stop_helper with #ifdef CONFIG_EXT_SUB_SCHED (only
> jumped to from within CONFIG_EXT_SUB_SCHED code):
>
> +#ifdef CONFIG_EXT_SUB_SCHED
> err_stop_helper:
> kthread_destroy_worker(sch->helper);
> +#endif
> err_free_pcpu:
>
> 3. Guard cgroup_get/cgroup_put in common paths with the existing
> CONFIG_EXT_GROUP_SCHED || CONFIG_EXT_SUB_SCHED pattern (matching
> the root_cgroup() / sch_cgroup() stubs):
>
> err_put_cgrp:
> +#if defined(CONFIG_EXT_GROUP_SCHED) || defined(CONFIG_EXT_SUB_SCHED)
> cgroup_put(cgrp);
> +#endif
>
> and:
>
> +#if defined(CONFIG_EXT_GROUP_SCHED) || defined(CONFIG_EXT_SUB_SCHED)
> cgroup_get(cgrp);
> +#endif
> sch = scx_alloc_and_add_sched(ops, cgrp, NULL);
>
> I verified this builds clean with both CGROUPS=y and CGROUPS=n.
>
> Thanks.
>
> --
> tejun
I have sent a v2 patch.
Thanks for explaining the dependency issue!
Link to v2:
https://lore.kernel.org/r/20260322063955.951848-1-yphbchou0911@gmail.com/
--
Thanks,
Cheng-Yang
^ permalink raw reply [flat|nested] 3+ messages in thread