Re: io_uring process termination/killing is not working

[Jens Axboe <axboe@kernel.dk>]

On 8/15/20 9:48 AM, Pavel Begunkov wrote:
> On 15/08/2020 18:12, Jens Axboe wrote:
>> On 8/15/20 12:45 AM, Pavel Begunkov wrote:
>>> On 13/08/2020 02:32, Jens Axboe wrote:
>>>> On 8/12/20 12:28 PM, Pavel Begunkov wrote:
>>>>> On 12/08/2020 21:22, Pavel Begunkov wrote:
>>>>>> On 12/08/2020 21:20, Pavel Begunkov wrote:
>>>>>>> On 12/08/2020 21:05, Jens Axboe wrote:
>>>>>>>> On 8/12/20 11:58 AM, Josef wrote:
>>>>>>>>> Hi,
>>>>>>>>>
>>>>>>>>> I have a weird issue on kernel 5.8.0/5.8.1, SIGINT even SIGKILL
>>>>>>>>> doesn't work to kill this process(always state D or D+), literally I
>>>>>>>>> have to terminate my VM because even the kernel can't kill the process
>>>>>>>>> and no issue on 5.7.12-201, however if IOSQE_IO_LINK is not set, it
>>>>>>>>> works
>>>>>>>>>
>>>>>>>>> I've attached a file to reproduce it
>>>>>>>>> or here
>>>>>>>>> https://gist.github.com/1Jo1/15cb3c63439d0c08e3589cfa98418b2c
>>>>>>>>
>>>>>>>> Thanks, I'll take a look at this. It's stuck in uninterruptible
>>>>>>>> state, which is why you can't kill it.
>>>>>>>
>>>>>>> It looks like one of the hangs I've been talking about a few days ago,
>>>>>>> an accept is inflight but can't be found by cancel_files() because it's
>>>>>>> in a link.
>>>>>>
>>>>>> BTW, I described it a month ago, there were more details.
>>>>>
>>>>> https://lore.kernel.org/io-uring/34eb5e5a-8d37-0cae-be6c-c6ac4d85b5d4@gmail.com
>>>>
>>>> Yeah I think you're right. How about something like the below? That'll
>>>> potentially cancel more than just the one we're looking for, but seems
>>>> kind of silly to only cancel from the file table holding request and to
>>>> the end.
>>>
>>> The bug is not poll/t-out related, IIRC my test reproduces it with
>>> read(pipe)->open(). See the previously sent link.
>>
>> Right, but in this context for poll, I just mean any request that has a
>> poll handler armed. Not necessarily only a pure poll. The patch should
>> fix your case, too.
> 
> Ok. I was thinking about sleeping in io_read(), etc. from io-wq context.
> That should have the same effect.

We already cancel any blocking work for the exiting task - but we do
that _after_ trying to cancel files, so we should probably just swap
those around in io_uring_flush(). That'll remove any need to find and
cancel those explicitly in io_uring_cancel_files().

-- 
Jens Axboe