> Il giorno 14 set 2022, alle ore 03:55, Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> ha scritto: > > > > 在 2022/09/07 9:16, Yu Kuai 写道: >> Hi, Paolo! >> 在 2022/09/06 17:37, Paolo Valente 写道: >>> >>> >>>> Il giorno 26 ago 2022, alle ore 04:34, Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> ha scritto: >>>> >>>> Hi, Paolo! >>>> >>>> 在 2022/08/25 22:59, Paolo Valente 写道: >>>>>> Il giorno 11 ago 2022, alle ore 03:19, Yu Kuai <yukuai1@xxxxxxxxxxxxxxx <mailto:yukuai1@xxxxxxxxxxxxxxx>> ha scritto: >>>>>> >>>>>> Hi, Paolo >>>>>> >>>>>> 在 2022/08/10 18:49, Paolo Valente 写道: >>>>>>>> Il giorno 27 lug 2022, alle ore 14:11, Yu Kuai <yukuai1@xxxxxxxxxxxxxxx <mailto:yukuai1@xxxxxxxxxxxxxxx>> ha scritto: >>>>>>>> >>>>>>>> Hi, Paolo >>>>>>>> >>>>>>> hi >>>>>>>> Are you still interested in this patchset? >>>>>>>> >>>>>>> Yes. Sorry for replying very late again. >>>>>>> Probably the last fix that you suggest is enough, but I'm a little bit >>>>>>> concerned that it may be a little hasty. In fact, before this fix, we >>>>>>> exchanged several messages, and I didn't seem to be very good at >>>>>>> convincing you about the need to keep into account also in-service >>>>>>> I/O. So, my question is: are you sure that now you have a >>>>>> >>>>>> I'm confused here, I'm pretty aware that in-service I/O(as said pending >>>>>> requests is the patchset) should be counted, as you suggested in v7, are >>>>>> you still thinking that the way in this patchset is problematic? >>>>>> >>>>>> I'll try to explain again that how to track is bfqq has pending pending >>>>>> requests, please let me know if you still think there are some problems: >>>>>> >>>>>> patch 1 support to track if bfqq has pending requests, it's >>>>>> done by setting the flag 'entity->in_groups_with_pending_reqs' when the >>>>>> first request is inserted to bfqq, and it's cleared when the last >>>>>> request is completed. specifically the flag is set in >>>>>> bfq_add_bfqq_busy() when 'bfqq->dispatched' if false, and it's cleared >>>>>> both in bfq_completed_request() and bfq_del_bfqq_busy() when >>>>>> 'bfqq->diapatched' is false. >>>>>> >>>>> This general description seems correct to me. Have you already sent a new version of your patchset? >>>> >>>> It's glad that we finially on the same page here. >>>> >>> >>> Yep. Sorry for my chronicle delay. >> Better late than never 😁 >>> >>>> Please take a look at patch 1, which already impelement the above >>>> descriptions, it seems to me there is no need to send a new version >>>> for now. If you think there are still some other problems, please let >>>> me know. >>>> >>> >>> Patch 1 seems ok to me. I seem to have only one pending comment on this patch (3/4) instead. Let me paste previous stuff here for your convenience: >> That sounds good. >>> >>>>> >>>>> - /* >>>>> - * Next function is invoked last, because it causes bfqq to be >>>>> - * freed if the following holds: bfqq is not in service and >>>>> - * has no dispatched request. DO NOT use bfqq after the next >>>>> - * function invocation. >>>>> - */ >>>> I would really love it if you leave this comment. I added it after >>>> suffering a lot for a nasty UAF. Of course the first sentence may >>>> need to be adjusted if the code that precedes it is to be removed. >>>> Same as above, if this patch is applied, this function will be gone. > > Hi, I'm curious while I'm trying to add the comment, before this > patchset, can bfqq be freed when bfq_weights_tree_remove is called? > > bfq_completed_request > bfqq->dispatched-- > if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) > bfq_weights_tree_remove(bfqd, bfqq); > > // continue to use bfqq > > It seems to me this is problematic if so, because bfqq is used after > bfq_weights_tree_remove() is called. > It is. Yet, IIRC, I verified that bfqq was not used after that free, and I added that comment as a heads-up. What is a scenario (before your pending modifications) where this use-after-free happens? Thanks, Paolo > Thanks, > Kuai
