Hi guys! On Wed 14-09-22 16:15:26, Yu Kuai wrote: > 在 2022/09/14 15:50, Paolo VALENTE 写道: > > > > > > > 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? > > > > No, it never happens, I just notice it because it'll be weird if I > place the comment where bfq_weights_tree_remove() is called, since bfqq > will still be accessed. > > If the suituation that the comment says is possible, perhaps we should > move bfq_weights_tree_remove() to the last of bfq_completed_request(). > However, it seems that we haven't meet the problem for quite a long > time... I'm bit confused which comment you are speaking about but bfq_completed_request() gets called only from bfq_finish_requeue_request() and the request itself still holds a reference to bfqq. Only later in bfq_finish_requeue_request() when we do: bfqq_request_freed(bfqq); bfq_put_queue(bfqq); bfqq can get freed. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
