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SubjectRe: [PATCH] blk-wbt: get back the missed wakeup from __wbt_done
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On 08/27/2018 11:52 AM, jianchao.wang wrote:
> 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 ?
>

If we do need a recheck after the io_schedule, we could do as following:

static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct,
unsigned long rw, spinlock_t *lock)
__releases(lock)
__acquires(lock)
{
struct rq_wait *rqw = get_rq_wait(rwb, wb_acct);
struct wbt_wait_data data = {
.wq = {
.func = wbt_wake_function,
.entry = LIST_HEAD_INIT(data.wq.entry),
},
.curr = current,
.rwb = rwb,
.rqw = rqw,
.rw = rw,
};
bool has_sleeper;
bool got = false;

retry:
has_sleeper = wq_has_sleeper(&rqw->wait);
if (!has_sleeper && rq_wait_inc_below(rqw, get_limit(rwb, rw)))
return;

prepare_to_wait_exclusive(&rqw->wait, &data.wq, TASK_UNINTERRUPTIBLE);

if (!has_sleeper && rq_wait_inc_below(rqw, get_limit(rwb, rw))) {
got = true;
goto out;
}

if (lock) {
spin_unlock_irq(lock);
io_schedule();
spin_lock_irq(lock);
} else
io_schedule();

out:
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 (data.got && got)
wbt_rqw_done(rwb, rqw, wb_acct);
else if (!data.got && !got)
goto retry;

Thanks
Jianchao

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