Re: [PATCH v10 14/21] jobs: protect job.aio_context with BQL and job_mutex

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

Am 17/08/2022 um 15:10 schrieb Emanuele Giuseppe Esposito:
> 
> 
> Am 17/08/2022 um 10:04 schrieb Emanuele Giuseppe Esposito:
>>>> +    /* protect against read in job_do_yield_locked */
>>>> +    JOB_LOCK_GUARD();
>>>> +    /* ensure the coroutine is quiescent while the AioContext is changed */
>>>> +    assert(job->pause_count > 0);
>>> job->pause_count only shows that pausing was requested. The coroutine is
>>> only really quiescent if job->busy == false, too.
>>>
>>> Or maybe job->paused is actually the one you want here.
>> I think job->paused works too.
>>
> 
> Actually it doesn't. At least test-block-iothread
> test_propagate_mirror() fails, for both job->paused and !job->busy. I
> think the reason is that if we wait for the flag to be set, we need to
> actually wait that the job gets to the next pause point, because
> job_pause() doesn't really pause the job, it just kind of "schedules"
> the pause on next pause point.
> 
> So, either we leave pause_count > 0, or somehow wait (I was thinking
> AIO_WAIT_WHILE(job->paused) but that's probably a very bad idea).
> 
> Do you have any suggestion for that?
> Maybe Paolo has a better idea on how to do it?
> 

Additional update: after debugging it a little bit, I figured that there
are places where busy=false and paused=false too. This is clear in
job_do_dismiss and not-so-clear in job_exit (at least for me).

I don't know if this is expected or a bug, because it just means that if
we are draining and the job is completing, there is no way to stop it.

Is it a bug? Or am I missing something?

Emanuele