[PATCH] sched/stats: TASK_IDLE task bypass the block_starts time

[Olice Zou]

For TASK_IDLE task, we not should record the block_starts, it is
not real TASK_UNINTERRUPTIBLE task.

It is easy to find this problem in a idle machine as followe:

bpftrace -e 'tracepoint:sched:sched_stat_blocked {  \
    if (args->delay > 1000000)  \
    {  \
	printf("%s %d\n", args->comm, args->delay);  \
	print(kstack());  \
    }  \
}

rcu_preempt 3881764
        __update_stats_enqueue_sleeper+604
        __update_stats_enqueue_sleeper+604
        enqueue_entity+1014
        enqueue_task_fair+156
        activate_task+109
        ttwu_do_activate+111
        try_to_wake_up+615
        wake_up_process+25
        process_timeout+22
        call_timer_fn+44
        run_timer_softirq+1100
        handle_softirqs+178
        irq_exit_rcu+113
        sysvec_apic_timer_interrupt+132
        asm_sysvec_apic_timer_interrupt+31
        pv_native_safe_halt+15
        arch_cpu_idle+13
        default_idle_call+48
        do_idle+516
        cpu_startup_entry+49
        start_secondary+280
        secondary_startup_64_no_verify+404

Signed-off-by: Olice Zou <olicezou@xxxxxxxxxxx>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a85539df75a5..e473e3244dda 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1285,7 +1285,7 @@ update_stats_dequeue_fair(struct cfs_rq *cfs_rq, struct sched_entity *se, int fl
 		if (state & TASK_INTERRUPTIBLE)
 			__schedstat_set(tsk->stats.sleep_start,
 				      rq_clock(rq_of(cfs_rq)));
-		if (state & TASK_UNINTERRUPTIBLE)
+		if (state != TASK_IDLE && (state & TASK_UNINTERRUPTIBLE))
 			__schedstat_set(tsk->stats.block_start,
 				      rq_clock(rq_of(cfs_rq)));
 	}
-- 
2.25.1