From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jann Horn <jannh@google.com>
Subject: Re: [PATCH 05/18] Add io_uring IO interface
Date: Tue, 29 Jan 2019 02:29:22 +0100
Message-ID: <CAG48ez2gvgBUKNihnjEWeBv1WZiXWwfxcA2Wf90n8GHLket2Mg@mail.gmail.com>
References: <20190128213538.13486-1-axboe@kernel.dk> <20190128213538.13486-6-axboe@kernel.dk>
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To: Jens Axboe <axboe@kernel.dk>
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On Mon, Jan 28, 2019 at 10:35 PM Jens Axboe <axboe@kernel.dk> wrote:
> The submission queue (SQ) and completion queue (CQ) rings are shared
> between the application and the kernel. This eliminates the need to
> copy data back and forth to submit and complete IO.
[...]
> +static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx)
> +{
> +       struct io_kiocb *req;
> +
> +       /* safe to use the non tryget, as we're inside ring ref already */
> +       percpu_ref_get(&ctx->refs);

Is that true? In the path io_sq_thread() -> io_submit_sqes() ->
io_submit_sqe() -> io_get_req(), I don't see anything that's already
holding a reference for you. Is the worker thread holding a reference
somewhere that I'm missing?

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