On 9/18/23 10:02 AM, Ming Lei wrote: > 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. Perfect, thanks Ming! -- Jens Axboe
