Hi Ming Thanks for your kindly response On 06/15/2018 12:03 PM, Ming Lei wrote: > On Fri, Jun 15, 2018 at 11:26 AM, jianchao.wang > <jianchao.w.wang@xxxxxxxxxx> wrote: >> Hi Ming >> >> On 06/15/2018 11:20 AM, Ming Lei wrote: >>> On Fri, Jun 15, 2018 at 11:04 AM, jianchao.wang >>> <jianchao.w.wang@xxxxxxxxxx> wrote: >>>> Hi Ming >>>> >>>> Thanks for your kindly response. >>>> >>>> On 06/15/2018 10:56 AM, Ming Lei wrote: >>>>>>> IMO, ref-counter is just to fix the blk-mq req life recycle issue. >>>>>>> It cannot replace the blk_mark_rq_complete which could avoid the race between >>>>>>> timeout and io completion path. >>>>>> The .timeout return BLK_EH_DONE doesn't always mean the request has been completed. >>>>>> Such as scsi-mid layer, its .timeout callback return BLK_EH_DONE but the timed out >>>>>> request is still in abort or eh process. What if a completion irq come during that ? >>>>> For blk-mq, it is avoided by the atomic state change in >>>>> __blk_mq_complete_request(), >>>>> that is why I mentioned the question in my last reply. >>>>> >>>> >>>> but blk_mq_check_expired doesn't do that. >>>> do I miss anything ? >>> >>> Right, that is the difference between blk-mq and legacy now, >> >> Sorry, I cannot follow your point. >> blk_mq_check_expired doesn't do a atmoc state change from IN-FLIGHT to COMPLETE. >> __blk_mq_complete_request could still proceed to complete a timed out request >> which is in scsi abort or eh process. Is it really OK ? > > That is the idea of Christoph's patchset of 'complete requests from ->timeout', Yes, I used to read that mail thread. > then drivers need to cover race between timeout and normal completeion. > > But at least the request won't be completed twice because of the atomic > state change in __blk_mq_complete_request(). Yes > > So what is your real concern about blk-mq's timeout? I concern whether the current drivers have bee ready for taking this task currently. At least, for scsi, if I try to trigger timeout and completion path concurrently, system would crash. 4.17.rc7 or 4.18 with a patch that change state in blk_mq_check_expired will survive. Thanks jianchao > > Thanks, > Ming >
