On 12/19/20 10:34 AM, Norman Maurer wrote: >> Am 19.12.2020 um 18:11 schrieb Jens Axboe <axboe@xxxxxxxxx>: >> >> On 12/19/20 9:29 AM, Jens Axboe wrote: >>>> On 12/19/20 9:13 AM, Jens Axboe wrote: >>>> On 12/18/20 7:49 PM, Josef wrote: >>>>>> I'm happy to run _any_ reproducer, so please do let us know if you >>>>>> manage to find something that I can run with netty. As long as it >>>>>> includes instructions for exactly how to run it :-) >>>>> >>>>> cool :) I just created a repo for that: >>>>> https://github.com/1Jo1/netty-io_uring-kernel-debugging.git >>>>> >>>>> - install jdk 1.8 >>>>> - to run netty: ./mvnw compile exec:java >>>>> -Dexec.mainClass="uring.netty.example.EchoUringServer" >>>>> - to run the echo test: cargo run --release -- --address >>>>> "127.0.0.1:2022" --number 200 --duration 20 --length 300 >>>>> (https://github.com/haraldh/rust_echo_bench.git) >>>>> - process kill -9 >>>>> >>>>> async flag is enabled and these operation are used: OP_READ, >>>>> OP_WRITE, OP_POLL_ADD, OP_CLOSE, OP_ACCEPT >>>>> >>>>> (btw you can change the port in EchoUringServer.java) >>>> >>>> This is great! Not sure this is the same issue, but what I see here is >>>> that we have leftover workers when the test is killed. This means the >>>> rings aren't gone, and the memory isn't freed (and unaccounted), which >>>> would ultimately lead to problems of course, similar to just an >>>> accounting bug or race. >>>> >>>> The above _seems_ to be related to IOSQE_ASYNC. Trying to narrow it >>>> down... >>> >>> Further narrowed down, it seems to be related to IOSQE_ASYNC on the >>> read requests. I'm guessing there are cases where we end up not >>> canceling them on ring close, hence the ring stays active, etc. >>> >>> If I just add a hack to clear IOSQE_ASYNC on IORING_OP_READ, then >>> the test terminates fine on the kill -9. >> >> And even more so, it's IOSQE_ASYNC on the IORING_OP_READ on an eventfd >> file descriptor. You probably don't want/mean to do that as it's >> pollable, I guess it's done because you just set it on all reads for the >> test? >> >> In any case, it should of course work. This is the leftover trace when >> we should be exiting, but an io-wq worker is still trying to get data >> from the eventfd: >> >> $ sudo cat /proc/2148/stack >> [<0>] eventfd_read+0x160/0x260 >> [<0>] io_iter_do_read+0x1b/0x40 >> [<0>] io_read+0xa5/0x320 >> [<0>] io_issue_sqe+0x23c/0xe80 >> [<0>] io_wq_submit_work+0x6e/0x1a0 >> [<0>] io_worker_handle_work+0x13d/0x4e0 >> [<0>] io_wqe_worker+0x2aa/0x360 >> [<0>] kthread+0x130/0x160 >> [<0>] ret_from_fork+0x1f/0x30 >> >> which will never finish at this point, it should have been canceled. > > Thanks a lot ... we can just workaround this than in netty . That probably should be done in any case, since I don't think IOSQE_ASYNC is useful on the eventfd read for you. But I'm trying to narrow down _why_ it fails, it could be a general issue in how cancelations are processed for sudden exit. Which would explain why it only shows up for the kill -9 case. Anyway, digging into it :-) -- Jens Axboe
