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

[Pavel Begunkov <asml.silence@gmail.com>]

On 20/12/2020 00:25, Jens Axboe wrote:
> On 12/19/20 4:42 PM, Pavel Begunkov wrote:
>> On 19/12/2020 23:13, Jens Axboe wrote:
>>> On 12/19/20 2:54 PM, Jens Axboe wrote:
>>>> On 12/19/20 1:51 PM, Josef wrote:
>>>>>> 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?
>>>>>
>>>>> yes exactly, eventfd fd is blocking, so it actually makes no sense to
>>>>> use IOSQE_ASYNC
>>>>
>>>> Right, and it's pollable too.
>>>>
>>>>> I just tested eventfd without the IOSQE_ASYNC flag, it seems to work
>>>>> in my tests, thanks a lot :)
>>>>>
>>>>>> 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:
>>>>>
>>>>> interesting, btw what kind of tool do you use for kernel debugging?
>>>>
>>>> Just poking at it and thinking about it, no hidden magic I'm afraid...
>>>
>>> Josef, can you try with this added? Looks bigger than it is, most of it
>>> is just moving one function below another.
>>
>> Hmm, which kernel revision are you poking? Seems it doesn't match
>> io_uring-5.10, and for 5.11 io_uring_cancel_files() is never called with
>> NULL files.
>>
>> if (!files)
>> 	__io_uring_cancel_task_requests(ctx, task);
>> else
>> 	io_uring_cancel_files(ctx, task, files);
> 
> Yeah, I think I messed up. If files == NULL, then the task is going away.
> So we should cancel all requests that match 'task', not just ones that
> match task && files.
> 
> Not sure I have much more time to look into this before next week, but
> something like that.
> 
> The problem case is the async worker being queued, long before the task
> is killed and the contexts go away. But from exit_files(), we're only
> concerned with canceling if we have inflight. Doesn't look right to me.

In theory all that should be killed in io_ring_ctx_wait_and_kill(),
of course that's if the ring itself is closed.

Guys, do you share rings between processes? Explicitly like sending 
io_uring fd over a socket, or implicitly e.g. sharing fd tables
(threads), or cloning with copying fd tables (and so taking a ref
to a ring).
In other words, if you kill all your io_uring applications, does it
go back to normal?

-- 
Pavel Begunkov