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SubjectRe: [PATCH] blk-wbt: get back the missed wakeup from __wbt_done
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Hi Jens

On 08/25/2018 11:41 PM, Jens Axboe wrote:
> do {
> - set_current_state(TASK_UNINTERRUPTIBLE);
> + if (test_bit(0, &data.flags))
> + break;
>
> - if (!has_sleeper && rq_wait_inc_below(rqw, get_limit(rwb, rw)))
> + WARN_ON_ONCE(list_empty(&data.wq.entry));
> +
> + if (!has_sleeper &&
> + rq_wait_inc_below(rqw, get_limit(rwb, rw))) {
> + finish_wait(&rqw->wait, &data.wq);
> +
> + /*
> + * We raced with wbt_wake_function() getting a token,
> + * which means we now have two. Put ours and wake
> + * anyone else potentially waiting for one.
> + */
> + if (test_bit(0, &data.flags))
> + wbt_rqw_done(rwb, rqw, wb_acct);
> break;

Just use 'bool' variable should be OK
After finish_wait, no one could race with us here.

> + }
>
> if (lock) {
> spin_unlock_irq(lock);
> @@ -511,11 +569,11 @@ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct,
> spin_lock_irq(lock);
> } else
> io_schedule();
> +
> has_sleeper = false;
> } while (1);

I cannot get the point of "since we can't rely on just being woken from the ->func handler
we set".
Do you mean there could be someone else could wake up this task ?

Thanks
Jianchao

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