On 5/2/22 7:59 AM, Jens Axboe wrote: > On 5/2/22 7:36 AM, Daniel Harding wrote: >> On 5/2/22 16:26, Jens Axboe wrote: >>> On 5/2/22 7:17 AM, Daniel Harding wrote: >>>> I use lxc-4.0.12 on Gentoo, built with io-uring support >>>> (--enable-liburing), targeting liburing-2.1. My kernel config is a >>>> very lightly modified version of Fedora's generic kernel config. After >>>> moving from the 5.16.x series to the 5.17.x kernel series, I started >>>> noticed frequent hangs in lxc-stop. It doesn't happen 100% of the >>>> time, but definitely more than 50% of the time. Bisecting narrowed >>>> down the issue to commit aa43477b040251f451db0d844073ac00a8ab66ee: >>>> io_uring: poll rework. Testing indicates the problem is still present >>>> in 5.18-rc5. Unfortunately I do not have the expertise with the >>>> codebases of either lxc or io-uring to try to debug the problem >>>> further on my own, but I can easily apply patches to any of the >>>> involved components (lxc, liburing, kernel) and rebuild for testing or >>>> validation. I am also happy to provide any further information that >>>> would be helpful with reproducing or debugging the problem. >>> Do you have a recipe to reproduce the hang? That would make it >>> significantly easier to figure out. >> >> I can reproduce it with just the following: >> >> sudo lxc-create --n lxc-test --template download --bdev dir --dir /var/lib/lxc/lxc-test/rootfs -- -d ubuntu -r bionic -a amd64 >> sudo lxc-start -n lxc-test >> sudo lxc-stop -n lxc-test >> >> The lxc-stop command never exits and the container continues running. >> If that isn't sufficient to reproduce, please let me know. > > Thanks, that's useful! I'm at a conference this week and hence have > limited amount of time to debug, hopefully Pavel has time to take a look > at this. Didn't manage to reproduce. Can you try, on both the good and bad kernel, to do: # echo 1 > /sys/kernel/debug/tracing/events/io_uring/enable run lxc-stop # cp /sys/kernel/debug/tracing/trace ~/iou-trace so we can see what's going on? Looking at the source, lxc is just using plain POLL_ADD, so I'm guessing it's not getting a notification when it expects to, or it's POLL_REMOVE not doing its job. If we have a trace from both a working and broken kernel, that might shed some light on it. -- Jens Axboe
