Re: [PATCH v2 15/13] sched_ext: Release cpus_read_lock on scx_link_sched() failure in root enable

Andrea Righi
2026-04-25T06:52:10Z

On Fri, Apr 24, 2026 at 02:19:51PM -1000, Tejun Heo wrote:
> scx_root_enable_workfn() takes cpus_read_lock() before
> scx_link_sched(sch), but the `if (ret) goto err_disable` on failure
> skips the matching cpus_read_unlock() - all other err_disable gotos
> along this path drop the lock first.
>
> scx_link_sched() only returns non-zero on the sub-sched path
> (parent != NULL), so the leak path is unreachable via the root
> caller today. Still, the unwind is out of line with the surrounding
> paths.
>
> Drop cpus_read_lock() before goto err_disable.
>
> v2: Correct Fixes: tag per Andrea Righi - the missing
> cpus_read_unlock() became a (latent) bug when scx_link_sched() was
> made fallible, not when err_disable was reorganized for hotplug.
>
> Fixes: 25037af712eb ("sched_ext: Add rhashtable lookup for sub-schedulers")
> Reported-by: Chris Mason <clm@meta.com>
> Signed-off-by: Tejun Heo <tj@kernel.org>

Reviewed-by: Andrea Righi <arighi@nvidia.com>

Thanks,
-Andrea

> ---
> kernel/sched/ext.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index f333fd0cb83f..9eda20e5fdb8 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -6736,8 +6736,10 @@ static void scx_root_enable_workfn(struct kthread_work *work)
> rcu_assign_pointer(scx_root, sch);
>
> ret = scx_link_sched(sch);
> - if (ret)
> + if (ret) {
> + cpus_read_unlock();
> goto err_disable;
> + }
>
> scx_idle_enable(ops);
>
> --
> 2.53.0
>