Re: [PATCH v4 10/20] sched/core: Push current task from non preferred CPU

[K Prateek Nayak <kprateek.nayak@amd.com>]

Hello Shrikanth,

On 6/17/2026 11:11 PM, Shrikanth Hegde wrote:
> +static int sched_non_preferred_cpu_push_stop(void *arg)
> +{
> +	struct task_struct *p = arg;
> +	struct rq *rq = this_rq();
> +	struct rq_flags rf;
> +	int cpu;
> +
> +	/* sanity check */
> +	if (cpu_preferred(rq->cpu))
> +		return 0;

I think this early return path should also clear "push_task_work_done"
indicator, otherwise, we will fail to schedule the stopper on this CPU
next time.

Also, we may need to add a context_unsafe_alias(rq) call here to keep
the context analysis bits happy similar to migration_cpu_stop().

> +
> +	raw_spin_lock_irq(&p->pi_lock);
> +	rq_lock(rq, &rf);
> +	rq->push_task_work_done = 0;
> +
> +	update_rq_clock(rq);
> +
> +	if (task_rq(p) == rq && task_on_rq_queued(p)) {
> +		cpu = select_fallback_rq(rq->cpu, p);

Do we need a task_has_preferred_cpus() sanity check here?

If the affinity changed before the stopper grabbed the p->pi_lock, and
there are no preferred CPUs to run on anymore, might as well keep the
task here instead of migrating it away.

> +		rq = __migrate_task(rq, &rf, p, cpu);
> +	}
> +
> +	rq_unlock(rq, &rf);
> +	raw_spin_unlock_irq(&p->pi_lock);
> +	put_task_struct(p);
> +
> +	return 0;
> +}

-- 
Thanks and Regards,
Prateek