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From: Jens Axboe <[email protected]>
To: Pavel Begunkov <[email protected]>,
	io-uring <[email protected]>
Subject: Re: [RFC] do_iopoll() and *grab_env()
Date: Fri, 12 Jun 2020 11:02:44 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 6/11/20 9:54 AM, Pavel Begunkov wrote:
> io_do_iopoll() can async punt a request with io_queue_async_work(),
> so doing io_req_work_grab_env(). The problem is that iopoll() can
> be called from who knows what context, e.g. from a completely
> different process with its own memory space, creds, etc.
> 
> io_do_iopoll() {
> 	ret = req->poll();
> 	if (ret == -EAGAIN)
> 		io_queue_async_work()
> 	...
> }
> 
> 
> I can't find it handled in io_uring. Can this even happen?
> Wouldn't it be better to complete them with -EAGAIN?

I don't think a plain -EAGAIN complete would be very useful, it's kind
of a shitty thing to pass back to userspace when it can be avoided. For
polled IO, we know we're doing O_DIRECT, or using fixed buffers. For the
latter, there's no problem in retrying, regardless of context. For the
former, I think we'd get -EFAULT mapping the IO at that point, which is
probably reasonable. I'd need to double check, though.

-- 
Jens Axboe


  reply	other threads:[~2020-06-12 17:02 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-11 15:54 [RFC] do_iopoll() and *grab_env() Pavel Begunkov
2020-06-12 17:02 ` Jens Axboe [this message]
2020-06-12 17:30   ` Pavel Begunkov
2020-06-12 17:55     ` Jens Axboe
2020-06-12 18:02       ` Jens Axboe
2020-06-12 18:33         ` Pavel Begunkov
2020-06-12 18:46           ` Pavel Begunkov
2020-06-12 19:42           ` Jens Axboe
2020-06-13 19:12             ` Pavel Begunkov

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