From: Jens Axboe <[email protected]>
To: Pavel Begunkov <[email protected]>, [email protected]
Subject: Re: [PATCH 2/8] io_uring: fix commit_cqring() locking in iopoll
Date: Tue, 30 Jun 2020 08:46:52 -0600 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On 6/30/20 8:36 AM, Pavel Begunkov wrote:
> 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()
For the IOPOLL setup, it should be protected by the ring mutex. Adding
the irq disable + lock for polling would be a nasty performance hit.
--
Jens Axboe
next prev parent reply other threads:[~2020-06-30 14:46 UTC|newest]
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
2020-06-30 14:46 ` Jens Axboe [this message]
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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