On Fri, Sep 01, 2023 at 08:47:28AM -0600, Jens Axboe wrote: > On 9/1/23 7:49 AM, Ming Lei wrote: > > io_wq_put_and_exit() is called from do_exit(), but all FIXED_FILE requests > > in io_wq aren't canceled in io_uring_cancel_generic() called from do_exit(). > > Meantime io_wq IO code path may share resource with normal iopoll code > > path. > > > > So if any HIPRI request is submittd via io_wq, this request may not get resouce > > for moving on, given iopoll isn't possible in io_wq_put_and_exit(). > > > > The issue can be triggered when terminating 't/io_uring -n4 /dev/nullb0' > > with default null_blk parameters. > > > > Fix it by always cancelling all requests in io_wq by adding helper of > > io_uring_cancel_wq(), and this way is reasonable because io_wq destroying > > follows canceling requests immediately. > > This does look much cleaner, but the unconditional cancel_all == true > makes me a bit nervous in case the ring is being shared. Here we just cancel requests in io_wq, which is per-task actually. Yeah, ctx->iopoll_ctx could be shared, but if it is used in this way, the event can't be avoided to reap from remote context. > > Do we really need to cancel these bits? Can't we get by with something > trivial like just stopping retrying if the original task is exiting? > > diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c > index c6d9e4677073..95316c0c3830 100644 > --- a/io_uring/io_uring.c > +++ b/io_uring/io_uring.c > @@ -1939,7 +1939,7 @@ void io_wq_submit_work(struct io_wq_work *work) > * If REQ_F_NOWAIT is set, then don't wait or retry with > * poll. -EAGAIN is final for that case. > */ > - if (req->flags & REQ_F_NOWAIT) > + if (req->flags & REQ_F_NOWAIT || req->task->flags & PF_EXITING) > break; This way isn't enough, any request submitted to io_wq before do_exit() need to be reaped by io_iopoll_try_reap_events() explicitly. Not mention IO_URING_F_NONBLOCK isn't set, so io_issue_sqe() may hang forever. Thanks, Ming
