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Thu, 10 Dec 2020 09:42:07 -0800 (PST) From: Pavel Begunkov To: Jens Axboe Cc: xiaoguang.wang@linux.alibaba.com, io-uring References: <10e20bd3-b08f-98b8-f857-8b9a75a511dd@kernel.dk> <33b5783d-c238-b0da-38cf-974736c36056@kernel.dk> <89d04d6b-2f84-82af-9ee7-edeb69f2a5bb@gmail.com> <7514e884-ce01-380c-5c06-f2331a4906bf@kernel.dk> 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 5.10 1/5] io_uring: always let io_iopoll_complete() complete polled io. Message-ID: <471ba4c7-2fcb-d42f-c40d-18bb916aef1f@gmail.com> Date: Thu, 10 Dec 2020 17:38:50 +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 09/12/2020 20:17, Pavel Begunkov wrote: > On 08/12/2020 21:10, Jens Axboe wrote: >> On 12/8/20 12:24 PM, Pavel Begunkov wrote: >>> On 08/12/2020 19:17, Jens Axboe wrote: >>>> On 12/8/20 12:12 PM, Pavel Begunkov wrote: >>>>> On 07/12/2020 16:28, Jens Axboe wrote: >>>>>> On Sun, Dec 6, 2020 at 3:26 PM Pavel Begunkov wrote: >>>>>>> From: Xiaoguang Wang >>>>>>> >>>>>>> The reason is that once we got a non EAGAIN error in io_wq_submit_work(), >>>>>>> we'll complete req by calling io_req_complete(), which will hold completion_lock >>>>>>> to call io_commit_cqring(), but for polled io, io_iopoll_complete() won't >>>>>>> hold completion_lock to call io_commit_cqring(), then there maybe concurrent >>>>>>> access to ctx->defer_list, double free may happen. >>>>>>> >>>>>>> To fix this bug, we always let io_iopoll_complete() complete polled io. >>>>>> >>>>>> This patch is causing hangs with iopoll testing, if you end up getting >>>>>> -EAGAIN on request submission. I've dropped it. >>>>> >>>>> I fail to understand without debugging how does it happen, especially since >>>>> it shouldn't even get out of the while in io_wq_submit_work(). Is that >>>>> something obvious I've missed? >>>> >>>> I didn't have time to look into it, and haven't yet, just reporting thation. >>>> it very reliably fails (and under what conditions). >>> >>> Yeah, I get it, asked just in case. >>> I'll see what's going on if Xiaoguang wouldn't handle it before. >> >> Should be trivial to reproduce on eg nvme by doing: >> >> echo mq-deadline > /sys/block/nvme0n1/queue/scheduler >> echo 2 > /sys/block/nvme0n1/queue/nr_requests >> >> and then run test/iopoll on that device. I'll try and take a look >> tomorrow unless someone beats me to it. > > Tried out with iopoll-enabled null_blk. test/iopoll fails with > "test_io_uring_submit_enters failed", but if remove iteration limit > from the test, it completes... eventually. > > premise: io_complete_rw_iopoll() gets -EAGAIN but returns 0 to > io_wq_submit_work(). > The old version happily completes IO with that 0, but the patch delays > it to do_iopoll(), which retries and so all that repeats. And, I believe, > that the behaviour that io_wq_submit_work()'s -EGAIN check was trying to > achieve... > > The question left is why no one progresses. May even be something in block. > Need to trace further. test_io_uring_submit_enters()'s io_uring_submit never goes into the kernel, IMHO it's saner to not expect to get any CQE, that's also implied in a comment above the function. I guess before we were getting blk-mq/etc. them back because of timers in blk-mq/etc. So I guess it should have been be more like the diff below, which still doesn't match the comment though. diff --git a/test/iopoll.c b/test/iopoll.c index d70ae56..d6f2f3e 100644 --- a/test/iopoll.c +++ b/test/iopoll.c @@ -269,13 +269,13 @@ static int test_io_uring_submit_enters(const char *file) /* submit manually to avoid adding IORING_ENTER_GETEVENTS */ ret = __sys_io_uring_enter(ring.ring_fd, __io_uring_flush_sq(&ring), 0, 0, NULL); - if (ret < 0) + if (ret != BUFFERS) goto err; for (i = 0; i < 500; i++) { - ret = io_uring_submit(&ring); - if (ret != 0) { - fprintf(stderr, "still had %d sqes to submit, this is unexpected", ret); + ret = io_uring_wait_cqe(&ring, &cqe); + if (ret < 0) { + fprintf(stderr, "wait cqe failed %i\n", ret); goto err; } -- Pavel Begunkov