Re: [PATCH 05/11] block: avoid ordered task state change for polled IO

[jianchao.wang]

Hi Jens

On 11/13/18 11:42 PM, Jens Axboe wrote:
> @@ -181,6 +181,7 @@ static void blkdev_bio_end_io_simple(struct bio *bio)
>       struct task_struct *waiter = bio->bi_private;
>  
>       WRITE_ONCE(bio->bi_private, NULL);
> +     smp_wmb();
>       wake_up_process(waiter);
>  }


The wake up path has contained a full memory barrier with the raw_spin_lock
and following smp_mb__after_spinlock

Please refer to:

wake_up_process
  -> try_to_wake_up

        raw_spin_lock_irqsave(&p->pi_lock, flags);
        smp_mb__after_spinlock();

So the smp_wmb here is not necessary.

Thanks
Jianchao