On Thu 16 Nov 2017 10:56:58 PM CET, John Snow wrote: >>>> I have the impression that one major source of headaches is the fact >>>> that the reopen queue contains nodes that don't need to be reopened at >>>> all. Ideally this should be detected early on in bdrv_reopen_queue(), so >>>> there's no chance that the queue contains nodes used by a different >>>> block job. If we had that then op blockers should be enough to prevent >>>> these things. Or am I missing something? >>>> >>> After applying Max's patch I tried the similar approach; that is keep >>> BDSes referenced while they are in the reopen queue. Now I get the >>> stream job hanging. Somehow one blk_root_drained_begin() is not paired >>> with blk_root_drained_end(). So the job stays paused. >> >> I can see this if I apply Max's patch and keep refs to BDSs in the >> reopen queue: >> >> #0 block_job_pause (...) at blockjob.c:130 >> #1 0x000055c143cb586d in block_job_drained_begin (...) at blockjob.c:227 >> #2 0x000055c143d08067 in blk_set_dev_ops (...) at block/block-backend.c:887 >> #3 0x000055c143cb69db in block_job_create (...) at blockjob.c:678 >> #4 0x000055c143d17c0c in mirror_start_job (...) at block/mirror.c:1177 >> >> There's a ops->drained_begin(opaque) call in blk_set_dev_ops() that >> doesn't seem to be paired. And when you call block_job_start() then it >> yields immediately waiting for the resume (that never arrives). >> >> John, this change was yours (f4d9cc88ee69a5b04). Any idea? > > The idea at the time was that if you tell the BlockBackend to drain and > then attach a job to it, once you go to *end* the drained region you'd > have a mismatched begin/end pair. > > To allow for some flexibility and to make sure that you *didn't* have a > mismatched begin/end call, what I did was that if you attach dev_ops to > an already drained backend (i.e. we "missed our chance" to issue the > drained_begin) we play catch-up and issue the drained call. > > There's no matching call here, because I anticipated whoever initially > bumped that quiesce_counter up to be issuing the drained_end, which will > then be propagated according to the dev_ops structure in place.
I see, thanks! Berto