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. 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. Thanks, Ming
