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From: Nadav Amit <nadav.amit@gmail.com>
To: Pavel Begunkov <asml.silence@gmail.com>
Cc: Olivier Langlois <olivier@trillion01.com>,
	Jens Axboe <axboe@kernel.dk>,
	io-uring@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] io_uring: clear TIF_NOTIFY_SIGNAL when running task work
Date: Tue, 10 Aug 2021 19:33:28 -0700	[thread overview]
Message-ID: <FD8FD9BD-1E94-4A84-88EB-3A1531BCF556@gmail.com> (raw)
In-Reply-To: <bbd25a42-eac0-a8f9-0e54-3c8c8e9894fd@gmail.com>



> On Aug 10, 2021, at 2:32 PM, Pavel Begunkov <asml.silence@gmail.com> wrote:
> 
> On 8/10/21 9:28 AM, Nadav Amit wrote:
>> 
>> Unfortunately, there seems to be yet another issue (unless my code
>> somehow caused it). It seems that when SQPOLL is used, there are cases
>> in which we get stuck in io_uring_cancel_sqpoll() when tctx_inflight()
>> never goes down to zero.
>> 
>> Debugging... (while also trying to make some progress with my code)
> 
> It's most likely because a request has been lost (mis-refcounted).
> Let us know if you need any help. Would be great to solve it for 5.14.
> quick tips: 
> 
> 1) if not already, try out Jens' 5.14 branch
> git://git.kernel.dk/linux-block io_uring-5.14
> 
> 2) try to characterise the io_uring use pattern. Poll requests?
> Read/write requests? Send/recv? Filesystem vs bdev vs sockets?
> 
> If easily reproducible, you can match io_alloc_req() with it
> getting into io_dismantle_req();

So actually the problem is more of a missing IO-uring functionality that I need. When an I/O is queued for async completion (i.e., after returning -EIOCBQUEUED), there should be a way for io-uring to cancel these I/Os if needed. Otherwise they might potentially never complete, as happens in my use-case.

AIO has ki_cancel() for this matter. So I presume the proper solution would be to move ki_cancel() from aio_kiocb to kiocb so it can be used by both io-uring and aio. And then - to use this infrastructure.

But it is messy. There is already a bug in the (few) uses of kiocb_set_cancel_fn() that blindly assume AIO is used and not IO-uring. Then, I am not sure about some things in the AIO code. Oh boy. I’ll work on an RFC.


  reply	other threads:[~2021-08-11  2:33 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-08  0:13 [PATCH 0/2] io_uring: bug fixes Nadav Amit
2021-08-08  0:13 ` [PATCH 1/2] io_uring: clear TIF_NOTIFY_SIGNAL when running task work Nadav Amit
2021-08-08 12:55   ` Pavel Begunkov
2021-08-08 17:31     ` Nadav Amit
2021-08-09  4:07       ` Hao Xu
2021-08-09  4:50         ` Nadav Amit
2021-08-09 10:35           ` Pavel Begunkov
2021-08-09 10:18       ` Pavel Begunkov
2021-08-09 21:48   ` Olivier Langlois
2021-08-10  8:28     ` Nadav Amit
2021-08-10 13:33       ` Olivier Langlois
2021-08-10 21:32       ` Pavel Begunkov
2021-08-11  2:33         ` Nadav Amit [this message]
2021-08-11  2:51           ` Jens Axboe
2021-08-11  5:40             ` I/O cancellation in io-uring (was: io_uring: clear TIF_NOTIFY_SIGNAL ...) Nadav Amit
2021-08-08  0:13 ` [PATCH 2/2] io_uring: Use WRITE_ONCE() when writing to sq_flags Nadav Amit
2021-08-09 13:53 ` [PATCH 0/2] io_uring: bug fixes Jens Axboe

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