On 9/1/23 9:12 AM, Ming Lei wrote: > 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. Ah yeah good point, it's just the tctx related bits. > 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. Yep it's not enough, and since we do only cancel per-task, I think this patch looks fine as-is and is probably the right way to go. Thanks Ming. -- Jens Axboe
