Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <35d9be6b-89ca-f2a1-ce5f-53e72610db6e@gmail.com>
Date:   Mon, 26 Sep 2022 20:12:57 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.12.0
Subject: Re: [PATCH v2 1/3] io_uring: register single issuer task at creation
Content-Language: en-US
To:     Dylan Yudaken <dylany@fb.com>, Jens Axboe <axboe@kernel.dk>
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>
From:   Pavel Begunkov <asml.silence@gmail.com>
In-Reply-To: <20220926170927.3309091-2-dylany@fb.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

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;


-- 
Pavel Begunkov