On Mon, Sep 18, 2023 at 08:15:07AM -0600, Jens Axboe wrote: > On 9/18/23 7:24 AM, Ming Lei wrote: > > On Mon, Sep 18, 2023 at 06:54:33AM -0600, Jens Axboe wrote: > >> On 9/17/23 10:10 PM, Ming Lei wrote: > >>> Hello, > >>> > >>> In do_exit(), io_uring needs to wait pending requests. > >>> > >>> ublk is one uring_cmd driver, and its usage is a bit special by submitting > >>> command for waiting incoming block IO request in advance, so if there > >>> isn't any IO request coming, the command can't be completed. So far ublk > >>> driver has to bind its queue with one ublk daemon server, meantime > >>> starts one monitor work to check if this daemon is live periodically. > >>> This way requires ublk queue to be bound one single daemon pthread, and > >>> not flexible, meantime the monitor work is run in 3rd context, and the > >>> implementation is a bit tricky. > >>> > >>> The 1st 3 patches adds io_uring task exit notifier, and the other > >>> patches converts ublk into this exit notifier, and the implementation > >>> becomes more robust & readable, meantime it becomes easier to relax > >>> the ublk queue/daemon limit in future, such as not require to bind > >>> ublk queue with single daemon. > >> > >> The normal approach for this is to ensure that each request is > >> cancelable, which we need for other things too (like actual cancel > >> support) Why can't we just do the same for ublk? > > > > I guess you meant IORING_OP_ASYNC_CANCEL, which needs userspace to > > submit this command, but here the userspace(ublk server) may be just panic > > or killed, and there isn't chance to send IORING_OP_ASYNC_CANCEL. > > Either that, or cancel done because of task exit. > > > And driver doesn't have any knowledge if the io_uring ctx or io task > > is exiting, so can't complete issued commands, then hang in > > io_uring_cancel_generic() when the io task/ctx is exiting. > > If you hooked into the normal cancel paths, you very much would get > notified when the task is exiting. That's how the other cancelations > work, eg if a task has pending poll requests and exits, they get > canceled and reaped. Ok, got the idea, thanks for the point! Turns out it is cancelable uring_cmd, and I will try to work towards this direction, and has got something in mind about the implementation. Thanks, Ming
