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Subject: Re: [PATCH] io_uring: fix ctx refcounting in io_submit_sqes()
From:   Pavel Begunkov <asml.silence@gmail.com>
To:     Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <8b53ce4539784423b493fdbfae9bd4c720b24d2a.1586120916.git.asml.silence@gmail.com>
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Message-ID: <331eb009-a8c3-98c7-4cec-d91a821f22be@gmail.com>
Date:   Mon, 6 Apr 2020 00:13:55 +0300
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From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org,
 linux-kernel@vger.kernel.org
Message-ID: <331eb009-a8c3-98c7-4cec-d91a821f22be@gmail.com>
Subject: Re: [PATCH] io_uring: fix ctx refcounting in io_submit_sqes()
References: <8b53ce4539784423b493fdbfae9bd4c720b24d2a.1586120916.git.asml.silence@gmail.com>
In-Reply-To: <8b53ce4539784423b493fdbfae9bd4c720b24d2a.1586120916.git.asml.silence@gmail.com>

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On 06/04/2020 00:08, Pavel Begunkov wrote:
> If io_get_req() fails, it drops a ref. Then, awhile keeping @submitted
> unmodified, io_submit_sqes() breaks the loop and puts @nr - @submitted
> refs. For each submitted req a ref is dropped in io_put_req() and
> friends. So, for @nr taken refs there will be
> (@nr - @submitted + @submitted + 1) dropped.
>=20
> Remove ctx refcounting from io_get_req(), that at the same time makes
> it clearer.

It seems, nobody hit OOM, so it stayed unnoticed. And neither did I.
It could be a good idea to do fault-injection for testing.

>=20
> Fixes: 2b85edfc0c90 ("io_uring: batch getting pcpu references")
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  fs/io_uring.c | 1 -
>  1 file changed, 1 deletion(-)
>=20
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 78ae8e8ed5bf..79bd22289d73 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -1342,7 +1342,6 @@ static struct io_kiocb *io_get_req(struct io_ring=
_ctx *ctx,
>  	req =3D io_get_fallback_req(ctx);
>  	if (req)
>  		goto got_it;
> -	percpu_ref_put(&ctx->refs);
>  	return NULL;
>  }
> =20
>=20

--=20
Pavel Begunkov


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