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Commit 7b76c244 authored by Srivatsa Vaddagiri's avatar Srivatsa Vaddagiri Committed by Steve Muckle
Browse files

sched: Fix possibility of "stuck" reserved flag 



check_for_migration() could mark a thread for migration (in
rq->push_task) and invoke active_load_balance_cpu_stop(). However that
thread could get migrated to another cpu by the time
active_load_balance_cpu_stop() runs, which could fail to clear
reserved flag for a cpu and drop task_sruct reference when cpu has
only one task (stopper thread running
active_load_balance_cpu_stop()). This would cause a cpu to have
reserved bit stuck, which prevents it from being used effectively.

Fix this by having active_load_balance_cpu_stop() drop reserved bit
always.

Change-Id: I2464a46b4ddb52376a95518bcc95dd9768e891f9
Signed-off-by: default avatarSrivatsa Vaddagiri <vatsa@codeaurora.org>
parent 0699a566

kernel/sched/fair.c

+8 −3
Original line number Diff line number Diff line
@@ -6723,14 +6723,12 @@ static int active_load_balance_cpu_stop(void *data) 
	double_lock_balance(busiest_rq, target_rq);



	push_task = busiest_rq->push_task;

	target_cpu = busiest_rq->push_cpu;

	if (push_task) {

		if (push_task->on_rq && push_task->state == TASK_RUNNING &&

		    task_cpu(push_task) == busiest_cpu &&

		    cpu_online(target_cpu))

			move_task(push_task, &env);

		put_task_struct(push_task);

		clear_reserved(target_cpu);

		busiest_rq->push_task = NULL;

		goto out_unlock_balance;

	}
@@ -6756,6 +6754,13 @@ out_unlock_balance: 
	double_unlock_balance(busiest_rq, target_rq);

out_unlock:

	busiest_rq->active_balance = 0;

	push_task = busiest_rq->push_task;

	target_cpu = busiest_rq->push_cpu;

	if (push_task) {

		put_task_struct(push_task);

		clear_reserved(target_cpu);

		busiest_rq->push_task = NULL;

	}

	raw_spin_unlock_irq(&busiest_rq->lock);

	if (per_cpu(dbs_boost_needed, target_cpu)) {

		struct migration_notify_data mnd;