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Sun, 05 Apr 2020 14:14:53 -0700 (PDT) Subject: Re: [PATCH] io_uring: fix ctx refcounting in io_submit_sqes() From: Pavel Begunkov To: Jens Axboe , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: <8b53ce4539784423b493fdbfae9bd4c720b24d2a.1586120916.git.asml.silence@gmail.com> Autocrypt: addr=asml.silence@gmail.com; prefer-encrypt=mutual; keydata= mQINBFmKBOQBEAC76ZFxLAKpDw0bKQ8CEiYJRGn8MHTUhURL02/7n1t0HkKQx2K1fCXClbps bdwSHrhOWdW61pmfMbDYbTj6ZvGRvhoLWfGkzujB2wjNcbNTXIoOzJEGISHaPf6E2IQx1ik9 6uqVkK1OMb7qRvKH0i7HYP4WJzYbEWVyLiAxUj611mC9tgd73oqZ2pLYzGTqF2j6a/obaqha +hXuWTvpDQXqcOZJXIW43atprH03G1tQs7VwR21Q1eq6Yvy2ESLdc38EqCszBfQRMmKy+cfp W3U9Mb1w0L680pXrONcnlDBCN7/sghGeMHjGKfNANjPc+0hzz3rApPxpoE7HC1uRiwC4et83 CKnncH1l7zgeBT9Oa3qEiBlaa1ZCBqrA4dY+z5fWJYjMpwI1SNp37RtF8fKXbKQg+JuUjAa9 Y6oXeyEvDHMyJYMcinl6xCqCBAXPHnHmawkMMgjr3BBRzODmMr+CPVvnYe7BFYfoajzqzq+h EyXSl3aBf0IDPTqSUrhbmjj5OEOYgRW5p+mdYtY1cXeK8copmd+fd/eTkghok5li58AojCba jRjp7zVOLOjDlpxxiKhuFmpV4yWNh5JJaTbwCRSd04sCcDNlJj+TehTr+o1QiORzc2t+N5iJ NbILft19Izdn8U39T5oWiynqa1qCLgbuFtnYx1HlUq/HvAm+kwARAQABtDFQYXZlbCBCZWd1 bmtvdiAoc2lsZW5jZSkgPGFzbWwuc2lsZW5jZUBnbWFpbC5jb20+iQJOBBMBCAA4FiEE+6Ju PTjTbx479o3OWt5b1Glr+6UFAlmKBOQCGwMFCwkIBwIGFQgJCgsCBBYCAwECHgECF4AACgkQ Wt5b1Glr+6WxZA//QueaKHzgdnOikJ7NA/Vq8FmhRlwgtP0+E+w93kL+ZGLzS/cUCIjn2f4Q Mcutj2Neg0CcYPX3b2nJiKr5Vn0rjJ/suiaOa1h1KzyNTOmxnsqE5fmxOf6C6x+NKE18I5Jy xzLQoktbdDVA7JfB1itt6iWSNoOTVcvFyvfe5ggy6FSCcP+m1RlR58XxVLH+qlAvxxOeEr/e aQfUzrs7gqdSd9zQGEZo0jtuBiB7k98t9y0oC9Jz0PJdvaj1NZUgtXG9pEtww3LdeXP/TkFl HBSxVflzeoFaj4UAuy8+uve7ya/ECNCc8kk0VYaEjoVrzJcYdKP583iRhOLlZA6HEmn/+Gh9 4orG67HNiJlbFiW3whxGizWsrtFNLsSP1YrEReYk9j1SoUHHzsu+ZtNfKuHIhK0sU07G1OPN 2rDLlzUWR9Jc22INAkhVHOogOcc5ajMGhgWcBJMLCoi219HlX69LIDu3Y34uIg9QPZIC2jwr 24W0kxmK6avJr7+n4o8m6sOJvhlumSp5TSNhRiKvAHB1I2JB8Q1yZCIPzx+w1ALxuoWiCdwV M/azguU42R17IuBzK0S3hPjXpEi2sK/k4pEPnHVUv9Cu09HCNnd6BRfFGjo8M9kZvw360gC1 reeMdqGjwQ68o9x0R7NBRrtUOh48TDLXCANAg97wjPoy37dQE7e5Ag0EWYoE5AEQAMWS+aBV IJtCjwtfCOV98NamFpDEjBMrCAfLm7wZlmXy5I6o7nzzCxEw06P2rhzp1hIqkaab1kHySU7g dkpjmQ7Jjlrf6KdMP87mC/Hx4+zgVCkTQCKkIxNE76Ff3O9uTvkWCspSh9J0qPYyCaVta2D1 Sq5HZ8WFcap71iVO1f2/FEHKJNz/YTSOS/W7dxJdXl2eoj3gYX2UZNfoaVv8OXKaWslZlgqN jSg9wsTv1K73AnQKt4fFhscN9YFxhtgD/SQuOldE5Ws4UlJoaFX/yCoJL3ky2kC0WFngzwRF Yo6u/KON/o28yyP+alYRMBrN0Dm60FuVSIFafSqXoJTIjSZ6olbEoT0u17Rag8BxnxryMrgR dkccq272MaSS0eOC9K2rtvxzddohRFPcy/8bkX+t2iukTDz75KSTKO+chce62Xxdg62dpkZX xK+HeDCZ7gRNZvAbDETr6XI63hPKi891GeZqvqQVYR8e+V2725w+H1iv3THiB1tx4L2bXZDI DtMKQ5D2RvCHNdPNcZeldEoJwKoA60yg6tuUquvsLvfCwtrmVI2rL2djYxRfGNmFMrUDN1Xq F3xozA91q3iZd9OYi9G+M/OA01husBdcIzj1hu0aL+MGg4Gqk6XwjoSxVd4YT41kTU7Kk+/I 5/Nf+i88ULt6HanBYcY/+Daeo/XFABEBAAGJAjYEGAEIACAWIQT7om49ONNvHjv2jc5a3lvU aWv7pQUCWYoE5AIbDAAKCRBa3lvUaWv7pfmcEACKTRQ28b1y5ztKuLdLr79+T+LwZKHjX++P 4wKjEOECCcB6KCv3hP+J2GCXDOPZvdg/ZYZafqP68Yy8AZqkfa4qPYHmIdpODtRzZSL48kM8 LRzV8Rl7J3ItvzdBRxf4T/Zseu5U6ELiQdCUkPGsJcPIJkgPjO2ROG/ZtYa9DvnShNWPlp+R uPwPccEQPWO/NP4fJl2zwC6byjljZhW5kxYswGMLBwb5cDUZAisIukyAa8Xshdan6C2RZcNs rB3L7vsg/R8UCehxOH0C+NypG2GqjVejNZsc7bgV49EOVltS+GmGyY+moIzxsuLmT93rqyII 5rSbbcTLe6KBYcs24XEoo49Zm9oDA3jYvNpeYD8rDcnNbuZh9kTgBwFN41JHOPv0W2FEEWqe JsCwQdcOQ56rtezdCJUYmRAt3BsfjN3Jn3N6rpodi4Dkdli8HylM5iq4ooeb5VkQ7UZxbCWt UVMKkOCdFhutRmYp0mbv2e87IK4erwNHQRkHUkzbsuym8RVpAZbLzLPIYK/J3RTErL6Z99N2 m3J6pjwSJY/zNwuFPs9zGEnRO4g0BUbwGdbuvDzaq6/3OJLKohr5eLXNU3JkT+3HezydWm3W OPhauth7W0db74Qd49HXK0xe/aPrK+Cp+kU1HRactyNtF8jZQbhMCC8vMGukZtWaAwpjWiiH bA== Message-ID: <331eb009-a8c3-98c7-4cec-d91a821f22be@gmail.com> Date: Mon, 6 Apr 2020 00:13:55 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <8b53ce4539784423b493fdbfae9bd4c720b24d2a.1586120916.git.asml.silence@gmail.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="LAAFwmJSbOmoVNvfVa9WANJQWhdlvKHW9" Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --LAAFwmJSbOmoVNvfVa9WANJQWhdlvKHW9 Content-Type: multipart/mixed; boundary="MpUJ3t078C23Yhln77CNhZqpcj2UdiCbZ"; protected-headers="v1" From: Pavel Begunkov To: Jens Axboe , 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> --MpUJ3t078C23Yhln77CNhZqpcj2UdiCbZ Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable 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 > --- > 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 --MpUJ3t078C23Yhln77CNhZqpcj2UdiCbZ-- --LAAFwmJSbOmoVNvfVa9WANJQWhdlvKHW9 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl6KShMACgkQWt5b1Glr +6UoOxAAsy645lj2RB08lPTdJNN8b996PhkC2pkZrUoccNFCnxegQD0rlJAsZnT+ OpVJipjd63C41eSd9Es9jOSbzT5twGCip1E+4V/yCWIcCRy7ZQg+ol5ieLtH7bDp XrienhiI72dIghdRzWP5oMQj0Th1ifx1uLpP56XSuAj0XPdvgUmNURiPHf2Dr7w0 jNBUeJLs9ezc4wgpRU4aXqMdBpI3vsqR2TrhwynRjTWThjR50bUf9Vt2jsqbegVw Z7myxGORCB9fMhooMH4iA9JVY4/RV1zraGNverWbQWyuY00Bqq0MNE5nbD7a5f/R VGQTOZj3neSFFnJiadXn8oxNrs8/4p8wha9D51LWq5y3X5M4T9fCr+YxaStFhI3y bvQIYYBu4M6EKrB93neYmhzpAEvjS24k4/7nUJHd5TNVddOyrfk5NiSzo9ynyrd8 GoTiHKgqnd+Yo9i69V6nHsmzo2MGOWwdkgxF8hZePvKE56YGcGSt17zk1ONpyrtJ AGIRIjf7U4kxLurlgo7yoXcSM1KEB5QcpDtRTZSOzMKRfwvzRWlPz4SXRHKPNNLw tsHhzsNA4qyNBOEy85hpYC+gQE6ZuIR1MDwoCtUkFIuioFSO/2DEtmuLD4AJ1jJ/ ypJ9dgrBKtRxEF5b+MuIr2IMwgppwJRDymWoLSPOU6tQ4q0id30= =bQ0Q -----END PGP SIGNATURE----- --LAAFwmJSbOmoVNvfVa9WANJQWhdlvKHW9--