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

[Jens Axboe <axboe@kernel.dk>]

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.

-- 
Jens Axboe