On Wed, May 29, 2019 at 08:36:46PM +0000, Vineeth Remanan Pillai wrote:
> + * The static-key + stop-machine variable are needed such that:
> + *
> + * spin_lock(rq_lockp(rq));
> + * ...
> + * spin_unlock(rq_lockp(rq));
> + *
> + * ends up locking and unlocking the _same_ lock, and all CPUs
> + * always agree on what rq has what lock.
> @@ -5790,8 +5854,15 @@ int sched_cpu_activate(unsigned int cpu)
> /*
> * When going up, increment the number of cores with SMT present.
> */
> - if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
> + if (cpumask_weight(cpu_smt_mask(cpu)) == 2) {
> static_branch_inc_cpuslocked(&sched_smt_present);
> +#ifdef CONFIG_SCHED_CORE
> + if (static_branch_unlikely(&__sched_core_enabled)) {
> + rq->core_enabled = true;
> + }
> +#endif
> + }
> +
> #endif
> set_cpu_active(cpu, true);
>
> @@ -5839,8 +5910,16 @@ int sched_cpu_deactivate(unsigned int cpu)
> /*
> * When going down, decrement the number of cores with SMT present.
> */
> - if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
> + if (cpumask_weight(cpu_smt_mask(cpu)) == 2) {
> +#ifdef CONFIG_SCHED_CORE
> + struct rq *rq = cpu_rq(cpu);
> + if (static_branch_unlikely(&__sched_core_enabled)) {
> + rq->core_enabled = false;
> + }
> +#endif
> static_branch_dec_cpuslocked(&sched_smt_present);
> +
> + }
> #endif
I'm confused, how doesn't this break the invariant above?
That is, all CPUs must at all times agree on the value of rq_lockp(),
and I'm not seeing how that is true with the above changes.
