Re: io_uring process termination/killing is not working

[Jens Axboe <axboe@kernel.dk>]

On 8/16/20 7:53 AM, Jens Axboe wrote:
> On 8/16/20 6:45 AM, Jens Axboe wrote:
>> 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().
> 
> I guess there's still the case of the task just closing the fd, not
> necessarily exiting. So I do agree with you that the io-wq case is still
> unhandled. I'll take a look...

The below should do it.


diff --git a/fs/io_uring.c b/fs/io_uring.c
index dc506b75659c..346a3eb84785 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8063,6 +8063,33 @@ static bool io_timeout_remove_link(struct io_ring_ctx *ctx,
 	return found;
 }
 
+static bool io_cancel_link_cb(struct io_wq_work *work, void *data)
+{
+	return io_match_link(container_of(work, struct io_kiocb, work), data);
+}
+
+static void io_attempt_cancel(struct io_ring_ctx *ctx, struct io_kiocb *req)
+{
+	enum io_wq_cancel cret;
+
+	/* cancel this particular work, if it's running */
+	cret = io_wq_cancel_work(ctx->io_wq, &req->work);
+	if (cret != IO_WQ_CANCEL_NOTFOUND)
+		return;
+
+	/* find links that hold this pending, cancel those */
+	cret = io_wq_cancel_cb(ctx->io_wq, io_cancel_link_cb, req, true);
+	if (cret != IO_WQ_CANCEL_NOTFOUND)
+		return;
+
+	/* if we have a poll link holding this pending, cancel that */
+	if (io_poll_remove_link(ctx, req))
+		return;
+
+	/* final option, timeout link is holding this req pending */
+	io_timeout_remove_link(ctx, req);
+}
+
 static void io_uring_cancel_files(struct io_ring_ctx *ctx,
 				  struct files_struct *files)
 {
@@ -8116,10 +8143,8 @@ static void io_uring_cancel_files(struct io_ring_ctx *ctx,
 				continue;
 			}
 		} else {
-			io_wq_cancel_work(ctx->io_wq, &cancel_req->work);
-			/* could be a link, check and remove if it is */
-			if (!io_poll_remove_link(ctx, cancel_req))
-				io_timeout_remove_link(ctx, cancel_req);
+			/* cancel this request, or head link requests */
+			io_attempt_cancel(ctx, cancel_req);
 			io_put_req(cancel_req);
 		}
 
-- 
Jens Axboe