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Wed, 06 Jan 2021 18:41:15 -0800 (PST) To: Bijan Mottahedeh , axboe@kernel.dk, io-uring@vger.kernel.org References: <1608314848-67329-1-git-send-email-bijan.mottahedeh@oracle.com> <1608314848-67329-9-git-send-email-bijan.mottahedeh@oracle.com> 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== Subject: Re: [PATCH v3 08/13] io_uring: implement fixed buffers registration similar to fixed files Message-ID: <66fd0092-2d03-02c0-fe1c-941c761a24f8@gmail.com> Date: Thu, 7 Jan 2021 02:37:45 +0000 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: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 06/01/2021 19:46, Bijan Mottahedeh wrote: > On 1/4/2021 6:43 PM, Pavel Begunkov wrote: >> On 18/12/2020 18:07, Bijan Mottahedeh wrote: >>> Apply fixed_rsrc functionality for fixed buffers support. >> >> git generated a pretty messy diff... > > I had tried to break this up a few ways but it didn't work well because I think most of the code changes depend on the io_uring structure changes.  I can look again or if you some idea of how you want to split it, I can do that. > >> Because it's do quiesce, fixed read/write access buffers from asynchronous >> contexts without synchronisation. That won't work anymore, so >> >> 1. either we save it in advance, that would require extra req_async >> allocation for linked fixed rw >> >> 2. or synchronise whenever async. But that would mean that a request >> may get and do IO on two different buffers, that's rotten. >> >> 3. do mixed -- lazy, but if do IO then alloc. >> >> 3.5 also "synchronise" there would mean uring_lock, that's not welcome, >> but we can probably do rcu. > > Are you referring to a case where a fixed buffer request can be submitted from async context while those buffers are being unregistered, or something like that? > >> Let me think of a patch... The most convenient API would be [1], it selects a buffer during submission, but allocates if needs to go async or for all linked requests. [2] should be correct from the kernel perspective (no races), it also solves doing IO on 2 different buffers, that's nasty (BTW, [1] solves this problem naturally). However, a buffer might be selected async, but the following can happen, and user should wait for request completion before removing a buffer. 1. register buf id=0 2. syscall io_uring_enter(submit=RW_FIXED,buf_id=0,IOSQE_ASYNC) 3. unregister buffers 4. the request may not find the buffer and fail. Not very convenient + can actually add overhead on the userspace side, can be even some heavy synchronisation. uring_lock in [2] is not nice, but I think I can replace it with rcu, probably can even help with sharing, but I need to try to implement to be sure. So that's an open question what API to have. Neither of diffs is tested. [1] diff --git a/fs/io_uring.c b/fs/io_uring.c index 7e35283fc0b1..2171836a9ce3 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -826,6 +826,7 @@ static const struct io_op_def io_op_defs[] = { .needs_file = 1, .unbound_nonreg_file = 1, .pollin = 1, + .needs_async_data = 1, .plug = 1, .async_size = sizeof(struct io_async_rw), .work_flags = IO_WQ_WORK_BLKCG | IO_WQ_WORK_MM, @@ -835,6 +836,7 @@ static const struct io_op_def io_op_defs[] = { .hash_reg_file = 1, .unbound_nonreg_file = 1, .pollout = 1, + .needs_async_data = 1, .plug = 1, .async_size = sizeof(struct io_async_rw), .work_flags = IO_WQ_WORK_BLKCG | IO_WQ_WORK_FSIZE | [2] diff --git a/fs/io_uring.c b/fs/io_uring.c index 7e35283fc0b1..31560b879fb3 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -3148,7 +3148,12 @@ static ssize_t io_import_iovec(int rw, struct io_kiocb *req, opcode = req->opcode; if (opcode == IORING_OP_READ_FIXED || opcode == IORING_OP_WRITE_FIXED) { *iovec = NULL; - return io_import_fixed(req, rw, iter); + + io_ring_submit_lock(req->ctx, needs_lock); + lockdep_assert_held(&req->ctx->uring_lock); + ret = io_import_fixed(req, rw, iter); + io_ring_submit_unlock(req->ctx, needs_lock); + return ret; } /* buffer index only valid with fixed read/write, or buffer select */ @@ -3638,7 +3643,7 @@ static int io_write(struct io_kiocb *req, bool force_nonblock, copy_iov: /* some cases will consume bytes even on error returns */ iov_iter_revert(iter, io_size - iov_iter_count(iter)); - ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false); + ret = io_setup_async_rw(req, iovec, inline_vecs, iter, true); if (!ret) return -EAGAIN; } -- Pavel Begunkov