Am 11.04.2019 um 19:20 hat Vladimir Sementsov-Ogievskiy geschrieben: > 11.04.2019 20:13, Vladimir Sementsov-Ogievskiy wrote: > > 11.04.2019 19:48, Kevin Wolf wrote: > >> Am 11.04.2019 um 16:48 hat Vladimir Sementsov-Ogievskiy geschrieben: > >>> 11.04.2019 17:15, Kevin Wolf wrote: > >>>> Am 11.04.2019 um 15:40 hat Vladimir Sementsov-Ogievskiy geschrieben: > >>>>> 25.02.2019 18:19, Kevin Wolf wrote: > >>>>>> bdrv_drain() must not leave connection_co scheduled, so bs->in_flight > >>>>>> needs to be increased while the coroutine is waiting to be scheduled > >>>>>> in the new AioContext after nbd_client_attach_aio_context(). > >>>>> > >>>>> Hi! > >>>>> > >>>>> I have some questions, could you explain, please? > >>>>> > >>>>> "bdrv_drain() must not leave connection_co scheduled" - it's because we > >>>>> want to be > >>>>> sure that connection_co yielded from nbd_read_eof, yes? > >>>>> > >>>>> But it is guaranteed by aio_wait_bh_oneshot.. Why do we need > >>>>> additioinally inc/dec > >>>>> bs->in_flight ? > >>>> > >>>> Without incrementing bs->in_flight, nothing would guarantee that > >>>> aio_poll() is called and the BH is actually executed before bdrv_drain() > >>>> returns. > >>> > >>> Don't follow.. Don't we want exactly this, we want BH to be executed > >>> while node is still > >>> drained, as you write in comment? > >> > >> Yes, exactly. But if bs->in_flight == 0, the AIO_WAIT_WHILE() condition > >> in the drain code could become false, so aio_poll() would not be called > >> again and drain would return even if the BH is still pending. > >> > > > > Ah, oops, sorry my English, I read it like "nothing would prevent". > > Understand now, thanks. > > Or not again.. We will not return to drain code, as we will loop in > aio_wait_bh_oneshot, > which will not return until BH handled
Oh, hm, good point, it's not just aio_bh_schedule_oneshot(), but the waiting version. I think I added the aio_wait_bh_oneshot() only later to address a review comment, so maybe increasing bs->in_flight isn't needed any more now. But it can't hurt at least... Kevin
