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[109.152.100.164]) by smtp.gmail.com with ESMTPSA id g17sm24445998wrw.37.2020.11.02.16.20.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Nov 2020 16:20:53 -0800 (PST) To: Jens Axboe , Vito Caputo , io-uring@vger.kernel.org References: <20201102205259.qsbp6yea3zfrqwuk@shells.gnugeneration.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: relative openat dirfd reference on submit Message-ID: <0532ec03-1dd2-a6ce-2a58-9e45d66435b5@gmail.com> Date: Tue, 3 Nov 2020 00:17:53 +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 03/11/2020 00:05, Jens Axboe wrote: > On 11/2/20 1:52 PM, Vito Caputo wrote: >> Hello list, >> >> I've been tinkering a bit with some async continuation passing style >> IO-oriented code employing liburing. This exposed a kind of awkward >> behavior I suspect could be better from an ergonomics perspective. >> >> Imagine a bunch of OPENAT SQEs have been prepared, and they're all >> relative to a common dirfd. Once io_uring_submit() has consumed all >> these SQEs across the syscall boundary, logically it seems the dirfd >> should be safe to close, since these dirfd-dependent operations have >> all been submitted to the kernel. >> >> But when I attempted this, the subsequent OPENAT CQE results were all >> -EBADFD errors. It appeared the submit didn't add any references to >> the dependent dirfd. >> >> To work around this, I resorted to stowing the dirfd and maintaining a >> shared refcount in the closures associated with these SQEs and >> executed on their CQEs. This effectively forced replicating the >> batched relationship implicit in the shared parent dirfd, where I >> otherwise had zero need to. Just so I could defer closing the dirfd >> until once all these closures had run on their respective CQE arrivals >> and the refcount for the batch had reached zero. >> >> It doesn't seem right. If I ensure sufficient queue depth and >> explicitly flush all the dependent SQEs beforehand >> w/io_uring_submit(), it seems like I should be able to immediately >> close(dirfd) and have the close be automagically deferred until the >> last dependent CQE removes its reference from the kernel side. > > We pass the 'dfd' straight on, and only the async part acts on it. > Which is why it needs to be kept open. But I wonder if we can get > around it by just pinning the fd for the duration. Since you didn't > include a test case, can you try with this patch applied? Totally > untested... afaik this doesn't pin an fd in a file table, so the app closes and dfd right after submit and then do_filp_open() tries to look up closed dfd. Doesn't seem to work, and we need to pass that struct file to do_filp_open(). > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index 1f555e3c44cd..b3a647dd206b 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -3769,6 +3769,9 @@ static int __io_openat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe > req->open.how.flags |= O_LARGEFILE; > > req->open.dfd = READ_ONCE(sqe->fd); > + if (req->open.dfd != -1 && req->open.dfd != AT_FDCWD) > + req->file = fget(req->open.dfd); > + > fname = u64_to_user_ptr(READ_ONCE(sqe->addr)); > req->open.filename = getname(fname); > if (IS_ERR(req->open.filename)) {o > @@ -3841,6 +3844,8 @@ static int io_openat2(struct io_kiocb *req, bool force_nonblock) > } > err: > putname(req->open.filename); > + if (req->file) > + fput(req->file); > req->flags &= ~REQ_F_NEED_CLEANUP; > if (ret < 0) > req_set_fail_links(req); > @@ -5876,6 +5881,8 @@ static void __io_clean_op(struct io_kiocb *req) > case IORING_OP_OPENAT2: > if (req->open.filename) > putname(req->open.filename); > + if (req->file) > + fput(req->file); > break; > } > req->flags &= ~REQ_F_NEED_CLEANUP; > -- Pavel Begunkov