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From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org
Subject: Re: [PATCH 2/8] io_uring: fix commit_cqring() locking in iopoll
Date: Tue, 30 Jun 2020 17:36:48 +0300
Message-ID: <6c499cf3-418d-2edf-d308-2bb5a8d1d007@gmail.com> (raw)
In-Reply-To: <65675178-365d-c859-426b-c0811a2647a3@kernel.dk>

On 30/06/2020 17:04, Jens Axboe wrote:
> On 6/30/20 6:20 AM, Pavel Begunkov wrote:
>> Don't call io_commit_cqring() without holding the completion spinlock
>> in io_iopoll_complete(), it can race, e.g. with async request failing.
> 
> Can you be more specific?

io_iopoll_complete()
	-> io_req_free_batch()
		-> io_queue_next()
			-> io_req_task_queue()
				-> task_work_add()

if this task_work_add() fails, it will be redirected to io-wq manager task
to do io_req_task_cancel() -> commit_cqring().


And probably something similar will happen if a request currently in io-wq
is retried with
io_rw_should_retry() -> io_async_buf_func() -> task_work_add()


I'll resend patch/series later with a better description. 

-- 
Pavel Begunkov

  reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-30 12:20 [PATCH 0/8] iopoll and task_work fixes Pavel Begunkov
2020-06-30 12:20 ` [PATCH 1/8] io_uring: fix io_fail_links() locking Pavel Begunkov
2020-06-30 14:38   ` Jens Axboe
2020-06-30 14:45     ` Pavel Begunkov
2020-06-30 12:20 ` [PATCH 2/8] io_uring: fix commit_cqring() locking in iopoll Pavel Begunkov
2020-06-30 14:04   ` Jens Axboe
2020-06-30 14:36     ` Pavel Begunkov [this message]
2020-06-30 14:46       ` Jens Axboe
2020-06-30 15:00         ` Pavel Begunkov
2020-06-30 15:33           ` Jens Axboe
2020-06-30 12:20 ` [PATCH 3/8] io_uring: fix ignoring eventfd " Pavel Begunkov
2020-06-30 12:20 ` [PATCH 4/8] io_uring: fix missing ->mm on exit Pavel Begunkov
2020-06-30 12:20 ` [PATCH 5/8] io_uring: don't fail iopoll requeue without ->mm Pavel Begunkov
2020-06-30 12:20 ` [PATCH 6/8] io_uring: fix NULL mm in io_poll_task_func() Pavel Begunkov
2020-06-30 12:20 ` [PATCH 7/8] io_uring: simplify io_async_task_func() Pavel Begunkov
2020-06-30 12:20 ` [PATCH 8/8] io_uring: optimise io_req_find_next() fast check Pavel Begunkov
2020-06-30 12:39 ` [PATCH 0/8] iopoll and task_work fixes Pavel Begunkov

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