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. -- Jens Axboe
