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Wed, 24 Feb 2021 01:50:09 -0800 (PST) To: Jens Axboe , Xiaoguang Wang , io-uring@vger.kernel.org Cc: joseph.qi@linux.alibaba.com References: <20210206150006.1945-1-xiaoguang.wang@linux.alibaba.com> <3e3cb8da-d925-7ebd-11a0-f9e145861962@linux.alibaba.com> <754563ed-5b2b-075d-16f8-d980e51102e6@linux.alibaba.com> <215e12a6-1aa7-c56f-1349-bd3828b225f6@kernel.dk> <7f52ca3a-b456-582e-c3db-99d2d028042f@linux.alibaba.com> <6a09434b-f975-cc49-cc6a-a5d369be325b@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== Subject: Re: [PATCH] io_uring: don't issue reqs in iopoll mode when ctx is dying Message-ID: Date: Wed, 24 Feb 2021 09:46:16 +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: <6a09434b-f975-cc49-cc6a-a5d369be325b@kernel.dk> 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 24/02/2021 02:51, Jens Axboe wrote: >>>>> On 08/02/2021 13:35, Pavel Begunkov wrote: >>>>>> On 08/02/2021 02:50, Xiaoguang Wang wrote: >>>>>>>>> The io_identity's count is underflowed. It's because in io_put_identity, >>>>>>>>> first argument tctx comes from req->task->io_uring, the second argument >>>>>>>>> comes from the task context that calls io_req_init_async, so the compare >>>>>>>>> in io_put_identity maybe meaningless. See below case: >>>>>>>>> task context A issue one polled req, then req->task = A. >>>>>>>>> task context B do iopoll, above req returns with EAGAIN error. >>>>>>>>> task context B re-issue req, call io_queue_async_work for req. >>>>>>>>> req->task->io_uring will set to task context B's identity, or cow new one. >>>>>>>>> then for above case, in io_put_identity(), the compare is meaningless. >>>>>>>>> >>>>>>>>> IIUC, req->task should indicates the initial task context that issues req, >>>>>>>>> then if it gets EAGAIN error, we'll call io_prep_async_work() in req->task >>>>>>>>> context, but iopoll reqs seems special, they maybe issued successfully and >>>>>>>>> got re-issued in other task context because of EAGAIN error. >>>>>>>> >>>>>>>> Looks as you say, but the patch doesn't solve the issue completely. >>>>>>>> 1. We must not do io_queue_async_work() under a different task context, >>>>>>>> because of it potentially uses a different set of resources. So, I just >>>>>>>> thought that it would be better to punt it to the right task context >>>>>>>> via task_work. But... >>>>>>>> >>>>>>>> 2. ...iovec import from io_resubmit_prep() might happen after submit ends, >>>>>>>> i.e. when iovec was freed in userspace. And that's not great at all. >>>>>>> Yes, agree, that's why I say we neeed to re-consider the io identity codes >>>>>>> more in commit message :) I'll have a try to prepare a better one. >>>>>> >>>>>> I'd vote for dragging -AGAIN'ed reqs that don't need io_import_iovec() >>>>>> through task_work for resubmission, and fail everything else. Not great, >>>>>> but imho better than always setting async_data. >>>>> >>>>> Hey Xiaoguang, are you working on this? I would like to leave it to you, >>>>> If you do. >>>> Sorry, currently I'm busy with other project and don't have much time to work on >>>> it yet. Hao Xu will help to continue work on the new version patch. >>> >>> Is it issue or reissue? I found this one today: >>> >>> https://lore.kernel.org/io-uring/c9f6e1f6-ff82-0e58-ab66-956d0cde30ff@kernel.dk/ >> Yeah, my initial patch is similar to yours, but it only solves the bug described >> in my commit message partially(ctx is dying), you can have a look at my commit message >> for the bug bug scene, thanks. > > Are you sure? We just don't want to reissue it, we need to fail it. > Hence if we catch it at reissue time, that should be enough. But I'm > open to clue batting :-) Jens, IOPOLL can happen from a different task, so 1) we don't want to grab io_wq_work context from it. As always we can pass it through task_work, or should be solved with your io-wq patches. 2) it happens who knows when in time, so iovec may be gone already -- same reasoning why io_[read,write]() copy it before going to io-wq. -- Pavel Begunkov