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

From: Emanuele Giuseppe Esposito
Subject: Re: [PATCH v10 14/21] jobs: protect job.aio_context with BQL and job_mutex
Date: Wed, 17 Aug 2022 15:10:38 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0

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?


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