From: Ingo Molnar <mingo@kernel.org>
Date: Wed, 17 Feb 2021 13:04:39 +0000 (+0100)
Subject: Merge tag 'v5.11' into sched/core, to pick up fixes & refresh the branch
X-Git-Tag: v5.12-rc1~147^2~35
X-Git-Url: https://repo.jachan.dev/linux.git/commitdiff_plain/ed3cd45f8ca873dd320ff7e6b4c1c8f83a65302c

Merge tag 'v5.11' into sched/core, to pick up fixes & refresh the branch

Signed-off-by: Ingo Molnar <mingo@kernel.org>
---

ed3cd45f8ca873dd320ff7e6b4c1c8f83a65302c
diff --cc kernel/sched/core.c
index 06b449942adf,ff74fca39ed2..6c789dcb8e5a
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@@ -7596,17 -7509,23 +7623,29 @@@ int sched_cpu_deactivate(unsigned int c
  	struct rq_flags rf;
  	int ret;
  
 +	/*
 +	 * Remove CPU from nohz.idle_cpus_mask to prevent participating in
 +	 * load balancing when not active
 +	 */
 +	nohz_balance_exit_idle(rq);
 +
  	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, wait for all preempt-disabled and RCU
- 	 * users of this state to go away such that all new such users will
- 	 * observe it.
+ 	 * 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.
+ 	 *
+ 	 * Specifically, we rely on ttwu to no longer target this CPU, see
+ 	 * ttwu_queue_cond() and is_cpu_allowed().
  	 *
  	 * Do sync before park smpboot threads to take care the rcu boost case.
  	 */
@@@ -7703,11 -7639,21 +7759,20 @@@ int sched_cpu_dying(unsigned int cpu
  	sched_tick_stop(cpu);
  
  	rq_lock_irqsave(rq, &rf);
- 	BUG_ON(rq->nr_running != 1 || rq_has_pinned_tasks(rq));
+ 	if (rq->nr_running != 1 || rq_has_pinned_tasks(rq)) {
+ 		WARN(true, "Dying CPU not properly vacated!");
+ 		dump_rq_tasks(rq, KERN_WARNING);
+ 	}
  	rq_unlock_irqrestore(rq, &rf);
  
+ 	/*
+ 	 * Now that the CPU is offline, make sure we're welcome
+ 	 * to new tasks once we come back up.
+ 	 */
+ 	balance_push_set(cpu, false);
+ 
  	calc_load_migrate(rq);
  	update_max_interval();
 -	nohz_balance_exit_idle(rq);
  	hrtick_clear(rq);
  	return 0;
  }