Use the new cpu_dying() state to simplify and fix the balance_push() vs CPU hotplug rollback state.
Specifically, we currently rely on notifiers sched_cpu_dying() / sched_cpu_activate() to terminate balance_push, however if the cpu_down() fails when we're past sched_cpu_deactivate(), it should terminate balance_push at that point and not wait until we hit sched_cpu_activate(). Signed-off-by: Peter Zijlstra (Intel) <[email protected]> --- kernel/sched/core.c | 33 ++++++++++++++++++++------------- kernel/sched/sched.h | 1 - 2 files changed, 20 insertions(+), 14 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1811,7 +1811,7 @@ static inline bool is_cpu_allowed(struct return cpu_online(cpu); /* Regular kernel threads don't get to stay during offline. */ - if (cpu_rq(cpu)->balance_push) + if (cpu_dying(cpu)) return false; /* But are allowed during online. */ @@ -7647,12 +7647,19 @@ static void balance_push(struct rq *rq) lockdep_assert_held(&rq->lock); SCHED_WARN_ON(rq->cpu != smp_processor_id()); + /* * Ensure the thing is persistent until balance_push_set(.on = false); */ rq->balance_callback = &balance_push_callback; /* + * Only active while going offline. + */ + if (!cpu_dying(rq->cpu)) + return; + + /* * Both the cpu-hotplug and stop task are in this case and are * required to complete the hotplug process. * @@ -7705,7 +7712,6 @@ static void balance_push_set(int cpu, bo struct rq_flags rf; rq_lock_irqsave(rq, &rf); - rq->balance_push = on; if (on) { WARN_ON_ONCE(rq->balance_callback); rq->balance_callback = &balance_push_callback; @@ -7830,8 +7836,8 @@ int sched_cpu_activate(unsigned int cpu) struct rq_flags rf; /* - * Make sure that when the hotplug state machine does a roll-back - * we clear balance_push. Ideally that would happen earlier... + * Clear the balance_push callback and prepare to schedule + * regular tasks. */ balance_push_set(cpu, false); @@ -7883,14 +7889,6 @@ int sched_cpu_deactivate(unsigned int cp set_cpu_active(cpu, false); /* - * From this point forward, this CPU will refuse to run any task that - * is not: migrate_disable() or KTHREAD_IS_PER_CPU, and will actively - * push those tasks away until this gets cleared, see - * sched_cpu_dying(). - */ - balance_push_set(cpu, true); - - /* * We've cleared cpu_active_mask / set balance_push, wait for all * preempt-disabled and RCU users of this state to go away such that * all new such users will observe it. @@ -7910,6 +7908,14 @@ int sched_cpu_deactivate(unsigned int cp } rq_unlock_irqrestore(rq, &rf); + /* + * From this point forward, this CPU will refuse to run any task that + * is not: migrate_disable() or KTHREAD_IS_PER_CPU, and will actively + * push those tasks away until this gets cleared, see + * sched_cpu_dying(). + */ + balance_push_set(cpu, true); + #ifdef CONFIG_SCHED_SMT /* * When going down, decrement the number of cores with SMT present. @@ -8206,7 +8212,7 @@ void __init sched_init(void) rq->sd = NULL; rq->rd = NULL; rq->cpu_capacity = rq->cpu_capacity_orig = SCHED_CAPACITY_SCALE; - rq->balance_callback = NULL; + rq->balance_callback = &balance_push_callback; rq->active_balance = 0; rq->next_balance = jiffies; rq->push_cpu = 0; @@ -8253,6 +8259,7 @@ void __init sched_init(void) #ifdef CONFIG_SMP idle_thread_set_boot_cpu(); + balance_push_set(smp_processor_id(), false); #endif init_sched_fair_class(); --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -982,7 +982,6 @@ struct rq { unsigned long cpu_capacity_orig; struct callback_head *balance_callback; - unsigned char balance_push; unsigned char nohz_idle_balance; unsigned char idle_balance;
