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Date:   Mon, 26 Sep 2022 13:40:20 -0600
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Subject: Re: [PATCH v2 1/3] io_uring: register single issuer task at creation
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To:     Pavel Begunkov <asml.silence@gmail.com>,
        Dylan Yudaken <dylany@fb.com>
Cc:     io-uring@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com
References: <20220926170927.3309091-1-dylany@fb.com>
 <20220926170927.3309091-2-dylany@fb.com>
 <35d9be6b-89ca-f2a1-ce5f-53e72610db6e@gmail.com>
From:   Jens Axboe <axboe@kernel.dk>
In-Reply-To: <35d9be6b-89ca-f2a1-ce5f-53e72610db6e@gmail.com>
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On 9/26/22 1:12 PM, Pavel Begunkov wrote:
> On 9/26/22 18:09, Dylan Yudaken wrote:
>> Instead of picking the task from the first submitter task, rather use the
>> creator task or in the case of disabled (IORING_SETUP_R_DISABLED) the
>> enabling task.
>>
>> This approach allows a lot of simplification of the logic here. This
>> removes init logic from the submission path, which can always be a bit
>> confusing, but also removes the need for locking to write (or read) the
>> submitter_task.
>>
>> Users that want to move a ring before submitting can create the ring
>> disabled and then enable it on the submitting task.
> 
> I think Dylan briefly mentioned before that it might be a good
> idea to task limit registration as well. I can't think of a use
> case at the moment but I agree we may find some in the future.
> 
> 
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index 242d896c00f3..60a471e43fd9 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -3706,6 +3706,9 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
>      if (WARN_ON_ONCE(percpu_ref_is_dying(&ctx->refs)))
>          return -ENXIO;
>  
> +    if (ctx->submitter_task && ctx->submitter_task != current)
> +        return -EEXIST;
> +
>      if (ctx->restricted) {
>          if (opcode >= IORING_REGISTER_LAST)
>              return -EINVAL;

Yes, I don't see any reason why not to enforce this for registration
too. Don't think there's currently a need to do so, but it'd be easy
to miss once we do add that. Let's queue that up for 6.1?

-- 
Jens Axboe