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Subject: Re: [PATCH 3/5] io_uring: fix reassigning work.task_pid from io-wq
To:     Pavel Begunkov <asml.silence@gmail.com>, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org
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 <4a08cc5a-2100-3a31-becb-c16592905c86@kernel.dk>
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From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <82bef6dc-608e-6fde-44fb-58ee517d234d@kernel.dk>
Date:   Tue, 11 Feb 2020 13:59:23 -0700
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On 2/11/20 1:57 PM, Pavel Begunkov wrote:
> On 11/02/2020 23:21, Jens Axboe wrote:
>> On 2/11/20 1:01 PM, Pavel Begunkov wrote:
>>> If a request got into io-wq context, io_prep_async_work() has already
>>> been called. Most of the stuff there is idempotent with an exception
>>> that it'll set work.task_pid to task_pid_vnr() of an io_wq worker thread
>>>
>>> Do only what's needed, that's io_prep_linked_timeout() and setting
>>> IO_WQ_WORK_UNBOUND.
>>
>> Rest of the series aside, I'm going to fix-up the pid addition to
>> only set if it's zero like the others.
> 
> IMO, io_req_work_grab_env() should never be called from io-wq. It'd do nothing
> good but open space for subtle bugs. And if that's enforced (as done in this
> patch), it's safe to set @pid multiple times.

I agree, it'd be an issue if we ever did the first iteration through the
worker. And it'd be nice to make the flow self explanatory in that
regard.

> Probably, it worth to add the check just to not go through task_pid_vnr()
> several times.

Good point, that is worth it on its own.

-- 
Jens Axboe