Re: "Cannot allocate memory" on ring creation (not RLIMIT_MEMLOCK)

[Norman Maurer <norman.maurer@googlemail.com>]

Thanks a lot ... we can just workaround this than in netty .

Bye
Norman 


> Am 19.12.2020 um 18:11 schrieb Jens Axboe <axboe@kernel.dk>:
> 
> 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.
> 
> -- 
> Jens Axboe
>