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

[Jens Axboe <axboe@kernel.dk>]

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.

-- 
Jens Axboe