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From: Kanchan Joshi <[email protected]>
To: Ming Lei <[email protected]>
Cc: Pavel Begunkov <[email protected]>,
	Jens Axboe <[email protected]>,
	[email protected]
Subject: Re: [PATCH] io_uring: complete request via task work in case of DEFER_TASKRUN
Date: Fri, 14 Apr 2023 19:43:15 +0530	[thread overview]
Message-ID: <20230414141315.GC5049@green5> (raw)
In-Reply-To: <[email protected]>

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On Fri, Apr 14, 2023 at 09:53:15PM +0800, Ming Lei wrote:
>On Fri, Apr 14, 2023 at 02:01:26PM +0100, Pavel Begunkov wrote:
>> On 4/14/23 08:53, Ming Lei wrote:
>> > So far io_req_complete_post() only covers DEFER_TASKRUN by completing
>> > request via task work when the request is completed from IOWQ.
>> >
>> > However, uring command could be completed from any context, and if io
>> > uring is setup with DEFER_TASKRUN, the command is required to be
>> > completed from current context, otherwise wait on IORING_ENTER_GETEVENTS
>> > can't be wakeup, and may hang forever.
>>
>> fwiw, there is one legit exception, when the task is half dead
>> task_work will be executed by a kthread. It should be fine as it
>> locks the ctx down, but I can't help but wonder whether it's only
>> ublk_cancel_queue() affected or there are more places in ublk?
>
>No, it isn't.
>
>It isn't triggered on nvme-pt just because command is always done
>in task context.
>
>And we know more uring command cases are coming.

FWIW, the model I had in mind (in initial days) was this -
1) io_uring_cmd_done is a simple API, it just posts one/two results into
reuglar/big SQE
2) for anything complex completion (that requires task-work), it will
use another API io_uring_cmd_complete_in_task with the provider-specific
callback (that will call above simple API eventually)


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  reply	other threads:[~2023-04-14 14:15 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20230414075422epcas5p3ae5de53e643a448f19df82a7a1d5cd1c@epcas5p3.samsung.com>
2023-04-14  7:53 ` [PATCH] io_uring: complete request via task work in case of DEFER_TASKRUN Ming Lei
2023-04-14 11:52   ` Kanchan Joshi
2023-04-14 12:39   ` Jens Axboe
2023-04-14 13:01   ` Pavel Begunkov
2023-04-14 13:53     ` Ming Lei
2023-04-14 14:13       ` Kanchan Joshi [this message]
2023-04-14 14:53         ` Ming Lei
2023-04-14 15:07       ` Pavel Begunkov
2023-04-14 15:42         ` Ming Lei
2023-04-15 23:15           ` Pavel Begunkov
2023-04-16 10:05             ` Ming Lei

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