On 2/9/18 6:21 AM, Oleksandr Natalenko wrote: > Hi. > > 08.02.2018 08:16, Paolo Valente wrote: >>> Il giorno 07 feb 2018, alle ore 23:18, Jens Axboe <ax...@kernel.dk> ha >>> scritto: >>> >>> On 2/7/18 2:19 PM, Paolo Valente wrote: >>>> Commit 'a6a252e64914 ("blk-mq-sched: decide how to handle flush rq >>>> via >>>> RQF_FLUSH_SEQ")' makes all non-flush re-prepared requests for a >>>> device >>>> be re-inserted into the active I/O scheduler for that device. As a >>>> consequence, I/O schedulers may get the same request inserted again, >>>> even several times, without a finish_request invoked on that request >>>> before each re-insertion. >>>> >>>> This fact is the cause of the failure reported in . For an I/O >>>> scheduler, every re-insertion of the same re-prepared request is >>>> equivalent to the insertion of a new request. For schedulers like >>>> mq-deadline or kyber, this fact causes no harm. In contrast, it >>>> confuses a stateful scheduler like BFQ, which keeps state for an I/O >>>> request, until the finish_request hook is invoked on the request. In >>>> particular, BFQ may get stuck, waiting forever for the number of >>>> request dispatches, of the same request, to be balanced by an equal >>>> number of request completions (while there will be one completion for >>>> that request). In this state, BFQ may refuse to serve I/O requests >>>> from other bfq_queues. The hang reported in  then follows. >>>> >>>> However, the above re-prepared requests undergo a requeue, thus the >>>> requeue_request hook of the active elevator is invoked for these >>>> requests, if set. This commit then addresses the above issue by >>>> properly implementing the hook requeue_request in BFQ. >>> >>> Thanks, applied. >>> >> >> I Jens, >> I forgot to add >> Tested-by: Oleksandr Natalenko <oleksa...@natalenko.name> >> in the patch. >> >> Is it still possible to add it? >> > > In addition to this I think it should be worth considering CC'ing Greg > to pull this fix into 4.15 stable tree.
I can't add the tested-by anymore, but it's easy enough to target for stable after-the-fact. -- Jens Axboe