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Date:   Mon, 26 Sep 2022 21:29:32 +0100
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Subject: Re: [PATCH v2 1/3] io_uring: register single issuer task at creation
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To:     Jens Axboe <axboe@kernel.dk>, Dylan Yudaken <dylany@fb.com>
Cc:     io-uring@vger.kernel.org, linux-kernel@vger.kernel.org,
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References: <20220926170927.3309091-1-dylany@fb.com>
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 <4623be74-d877-9042-f876-09feba2f0587@kernel.dk>
From:   Pavel Begunkov <asml.silence@gmail.com>
In-Reply-To: <4623be74-d877-9042-f876-09feba2f0587@kernel.dk>
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On 9/26/22 20:40, Jens Axboe wrote:
> 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?

6.1 + stable sounds ok, I don't have an opinion on how to how
to merge it.

-- 
Pavel Begunkov