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Mon, 27 Jan 2020 15:26:04 -0800 (PST) Subject: Re: [PATCHSET 0/4] Add support for shared io-wq backends To: Jens Axboe , Daurnimator Cc: io-uring@vger.kernel.org References: <20200123231614.10850-1-axboe@kernel.dk> <4917a761-6665-0aa2-0990-9122dfac007a@gmail.com> <694c2b6f-6b51-fd7b-751e-db87de90e490@kernel.dk> <92e92002-f803-819a-5f5e-44cf09e63c9b@kernel.dk> <3b3b5e03-2c7e-aa00-c1fd-3af8b2620d5e@gmail.com> <1b24da2d-dd92-608e-27b6-b827a728e7ab@kernel.dk> <18d3f936-c8d0-9bbb-6e9d-4c9ec579cfa4@kernel.dk> From: Pavel Begunkov 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: Date: Tue, 28 Jan 2020 02:25:29 +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: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="T0MF5BZwl5ZT8AL2SQYzmv3ONdfC0o9VA" 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) --T0MF5BZwl5ZT8AL2SQYzmv3ONdfC0o9VA Content-Type: multipart/mixed; boundary="al2Ov6Caw02o2ygydK5VkqFFVIy7hSNpB"; protected-headers="v1" From: Pavel Begunkov To: Jens Axboe , Daurnimator Cc: io-uring@vger.kernel.org Message-ID: Subject: Re: [PATCHSET 0/4] Add support for shared io-wq backends References: <20200123231614.10850-1-axboe@kernel.dk> <4917a761-6665-0aa2-0990-9122dfac007a@gmail.com> <694c2b6f-6b51-fd7b-751e-db87de90e490@kernel.dk> <92e92002-f803-819a-5f5e-44cf09e63c9b@kernel.dk> <3b3b5e03-2c7e-aa00-c1fd-3af8b2620d5e@gmail.com> <1b24da2d-dd92-608e-27b6-b827a728e7ab@kernel.dk> <18d3f936-c8d0-9bbb-6e9d-4c9ec579cfa4@kernel.dk> In-Reply-To: --al2Ov6Caw02o2ygydK5VkqFFVIy7hSNpB Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 28/01/2020 02:23, Jens Axboe wrote: > On 1/27/20 4:17 PM, Pavel Begunkov wrote: >> On 28/01/2020 02:00, Jens Axboe wrote: >>> On 1/27/20 3:40 PM, Jens Axboe wrote: >>>> On 1/27/20 2:45 PM, Pavel Begunkov wrote: >>>>> On 27/01/2020 23:33, Jens Axboe wrote: >>>>>> On 1/27/20 7:07 AM, Pavel Begunkov wrote: >>>>>>> On 1/27/2020 4:39 PM, Jens Axboe wrote: >>>>>>>> On 1/27/20 6:29 AM, Pavel Begunkov wrote: >>>>>>>>> On 1/26/2020 8:00 PM, Jens Axboe wrote: >>>>>>>>>> On 1/26/20 8:11 AM, Pavel Begunkov wrote: >>>>>>>>>>> On 1/26/2020 4:51 AM, Daurnimator wrote: >>>>>>>>>>>> On Fri, 24 Jan 2020 at 10:16, Jens Axboe w= rote: >>>>>>>>> Ok. I can't promise it'll play handy for sharing. Though, you'l= l be out >>>>>>>>> of space in struct io_uring_params soon anyway. >>>>>>>> >>>>>>>> I'm going to keep what we have for now, as I'm really not imagin= ing a >>>>>>>> lot more sharing - what else would we share? So let's not over-d= esign >>>>>>>> anything. >>>>>>>> >>>>>>> Fair enough. I prefer a ptr to an extendable struct, that will ta= ke the >>>>>>> last u64, when needed. >>>>>>> >>>>>>> However, it's still better to share through file descriptors. It'= s just >>>>>>> not secure enough the way it's now. >>>>>> >>>>>> Is the file descriptor value really a good choice? We just had som= e >>>>>> confusion on ring sharing across forks. Not sure using an fd value= >>>>>> is a sane "key" to use across processes. >>>>>> >>>>> As I see it, the problem with @mm is that uring is dead-bound to it= =2E >>>>> For example, a process can create and send uring (e.g. via socket),= >>>>> and then be killed. And that basically means >>>>> 1. @mm of the process is locked just because of the sent uring >>>>> instance. >>>>> 2. a process may have an io_uring, which bound to @mm of another >>>>> process, even though the layouts may be completely different. >>>>> >>>>> File descriptors are different here, because io_uring doesn't know >>>>> about them, They are controlled by the userspace (send, dup, fork, >>>>> etc), and don't sabotage all isolation work done in the kernel. A d= ire >>>>> example here is stealing io-wq from within a container, which is >>>>> trivial with global self-made id. I would love to hear, if I am >>>>> mistaken somewhere. >>>>> >>>>> Is there some better option? >>>> >>>> OK, so how about this: >>>> >>>> - We use the 'fd' as the lookup key. This makes it easy since we can= >>>> just check if it's a io_uring instance or not, we don't need to do= any >>>> tracking on the side. It also means that the application asking fo= r >>>> sharing must already have some relationship to the process that >>>> created the ring. >> >> Yeah, that's exactly the point. >> >>>> >>>> - mm/creds must be transferred through the work item. Any SQE done o= n >>>> behalf of io_uring_enter() directly already has that, if punted we= >>>> must pass the creds and mm. This means we break the static setup o= f >>>> io_wq->mm/creds. It also means that we probably have to add that t= o >>>> io_wq_work, which kind of sucks, but... >> >> ehh, juggling mm's... But don't have anything nicer myself. >=20 > We already do juggle mm's, this is no different. A worker potentially > retain the mm across works if they are the same. >=20 >>> It'd fix Stefan's worry too. >>> >>>> I think with that we have a decent setup, that's also safe. I've dro= pped >>>> the sharing patches for now, from the 5.6 tree. >>> >>> So one concern might be SQPOLL, it'll have to use the ctx creds and m= m >>> as usual. I guess that is ok. >>> >> >> OK. I'll send the patches for the first part now, and take a look at >> the second one a bit latter if isn't done until then. >=20 > Hang on a second, I'm doing the mm and creds bits right now. I'll push > that to a branch, if you want to do the actual fd stuff on top of that,= > that would be great. >=20 Sure, should be trivially mergeable. --=20 Pavel Begunkov --al2Ov6Caw02o2ygydK5VkqFFVIy7hSNpB-- --T0MF5BZwl5ZT8AL2SQYzmv3ONdfC0o9VA Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl4vcWkACgkQWt5b1Glr +6VZ9A//eMgEzfJa97oWWJlwiYCTuF+JofkP5Y7lBxc/NosSWdh8sUWs1Kle0TUp I5lb015xJRcjl+wJC7dSg95PuAWw6+0DrsvFkvdRMQw2NYtc+T2EIEGuqTw/qzpA EB2cgWhmEeTTj3WvUIhyCNJ4lui/Zgp7nfkHwaoHTWI/old9opvoesRLcS+f37k3 b7Ks8iEyFtvI34k7gXBHtfsunlCPd/QUD1iAHAZG7fUGGaHPZC+hFgeA1q/Zb2aK a8hIvFPaj7rrw2Ta1VEGM0iPantvNunRX7Yd2Jp96bZLrLg0jZLyJ0z2GgzyLRC1 QSccJRD1sMpRwjjvA84WZim9mFRg+WWRBWMVpuArzmyhWjOGR6DA4YCBwWv6LdQj WdoBEQotFHRXz7/P/HCvf6YDKIqqc8PHelFKjDAgVbse6lqm7r/TpcUCZUYSTrKT hLnqnK6p6s6+0hx8VZY6VeB9tAR+JQWL3xC37zsbGlslbawqpQ1bwRAvOZeURG36 rECz7fRKSQishJCTnHM/s6q4N9KMP0JayXh/u5vfF59EyOCbji5DeQcugK7hNxiG 0Qdg5yxXeIA93UQ6oFWwBOxu2KiDhojL+zxvlrF1DDawgukp3Zcd2ylLs0g4jYFr Nga/CaDVftLgTE8QOHhqzIMWEHPsriobEzoG3HomMj/X0esNdVc= =kIcL -----END PGP SIGNATURE----- --T0MF5BZwl5ZT8AL2SQYzmv3ONdfC0o9VA--