sched/rt: Fix bad task migration for rt tasks
Commit95158a89dd
("sched,rt: Use the full cpumask for balancing") allows find_lock_lowest_rq() to pick a task with migration disabled. The purpose of the commit is to push the current running task on the CPU that has the migrate_disable() task away. However, there is a race which allows a migrate_disable() task to be migrated. Consider: CPU0 CPU1 push_rt_task check is_migration_disabled(next_task) task not running and migration_disabled == 0 find_lock_lowest_rq(next_task, rq); _double_lock_balance(this_rq, busiest); raw_spin_rq_unlock(this_rq); double_rq_lock(this_rq, busiest); <<wait for busiest rq>> <wakeup> task become running migrate_disable(); <context out> deactivate_task(rq, next_task, 0); set_task_cpu(next_task, lowest_rq->cpu); WARN_ON_ONCE(is_migration_disabled(p)); Fixes:95158a89dd
("sched,rt: Use the full cpumask for balancing") Signed-off-by: Schspa Shi <schspa@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Dwaine Gonyier <dgonyier@redhat.com>
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@ -2246,6 +2246,7 @@ static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq)
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!cpumask_test_cpu(later_rq->cpu, &task->cpus_mask) ||
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task_on_cpu(rq, task) ||
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!dl_task(task) ||
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is_migration_disabled(task) ||
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!task_on_rq_queued(task))) {
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double_unlock_balance(rq, later_rq);
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later_rq = NULL;
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@ -2000,11 +2000,15 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
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* the mean time, task could have
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* migrated already or had its affinity changed.
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* Also make sure that it wasn't scheduled on its rq.
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* It is possible the task was scheduled, set
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* "migrate_disabled" and then got preempted, so we must
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* check the task migration disable flag here too.
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*/
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if (unlikely(task_rq(task) != rq ||
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!cpumask_test_cpu(lowest_rq->cpu, &task->cpus_mask) ||
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task_on_cpu(rq, task) ||
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!rt_task(task) ||
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is_migration_disabled(task) ||
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!task_on_rq_queued(task))) {
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double_unlock_balance(rq, lowest_rq);
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