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Sat, 06 Jun 2020 09:40:23 -0700 (PDT) From: Pavel Begunkov To: Xiaoguang Wang , io-uring@vger.kernel.org Cc: axboe@kernel.dk, joseph.qi@linux.alibaba.com References: <20200606151248.17663-1-xiaoguang.wang@linux.alibaba.com> <350132ea-aade-27f4-1fcc-ba0539a459a1@gmail.com> 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: execute task_work_run() before dropping mm Message-ID: <580b69a6-671e-d917-ca69-04588447f61d@gmail.com> Date: Sat, 6 Jun 2020 19:39:04 +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: <350132ea-aade-27f4-1fcc-ba0539a459a1@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 06/06/2020 18:55, Pavel Begunkov wrote: > On 06/06/2020 18:12, Xiaoguang Wang wrote: >> While testing io_uring in our internal kernel, note it's not upstream >> kernel, we see below panic: >> [ 872.498723] x29: ffff00002d553cf0 x28: 0000000000000000 >> [ 872.508973] x27: ffff807ef691a0e0 x26: 0000000000000000 >> [ 872.519116] x25: 0000000000000000 x24: ffff0000090a7980 >> [ 872.529184] x23: ffff000009272060 x22: 0000000100022b11 >> [ 872.539144] x21: 0000000046aa5668 x20: ffff80bee8562b18 >> [ 872.549000] x19: ffff80bee8562080 x18: 0000000000000000 >> [ 872.558876] x17: 0000000000000000 x16: 0000000000000000 >> [ 872.568976] x15: 0000000000000000 x14: 0000000000000000 >> [ 872.578762] x13: 0000000000000000 x12: 0000000000000000 >> [ 872.588474] x11: 0000000000000000 x10: 0000000000000c40 >> [ 872.598324] x9 : ffff000008100c00 x8 : 000000007ffff000 >> [ 872.608014] x7 : ffff80bee8562080 x6 : ffff80beea862d30 >> [ 872.617709] x5 : 0000000000000000 x4 : ffff80beea862d48 >> [ 872.627399] x3 : ffff80bee8562b18 x2 : 0000000000000000 >> [ 872.637044] x1 : ffff0000090a7000 x0 : 0000000000208040 >> [ 872.646575] Call trace: >> [ 872.653139] task_numa_work+0x4c/0x310 >> [ 872.660916] task_work_run+0xb0/0xe0 >> [ 872.668400] io_sq_thread+0x164/0x388 >> [ 872.675829] kthread+0x108/0x138 >> >> The reason is that once io_sq_thread has a valid mm, schedule subsystem >> may call task_tick_numa() adding a task_numa_work() callback, which will >> visit mm, then above panic will happen. >> >> To fix this bug, only call task_work_run() before dropping mm. > > So, the problem is that poll/async paths re-issue requests with > __io_queue_sqe(), which doesn't care about current->mm, and which > can be NULL for io_sq_thread(). Right? > >> >> Signed-off-by: Xiaoguang Wang >> --- >> fs/io_uring.c | 15 ++++++++------- >> 1 file changed, 8 insertions(+), 7 deletions(-) >> >> diff --git a/fs/io_uring.c b/fs/io_uring.c >> index 6391a00ff8b7..32381984b2a6 100644 >> --- a/fs/io_uring.c >> +++ b/fs/io_uring.c >> @@ -6134,6 +6134,13 @@ static int io_sq_thread(void *data) >> * to enter the kernel to reap and flush events. >> */ >> if (!to_submit || ret == -EBUSY) { >> + /* >> + * Current task context may already have valid mm, that >> + * means some works that visit mm may have been queued, >> + * so we must execute the works before dropping mm. >> + */ >> + if (current->task_works) >> + task_work_run(); > > Even though you're not dropping mm, the thread might not have it in the first > place. see how it's done in io_init_req(). How about setting mm either lazily > in io_poll_task_func()/io_async_task_func(), or before task_work_run() in > io_sq_thread(). Thinking about use_mm(), it's more about setting up env before execution rather than request intialisation. Another way would be to move use_mm() from io_init_req() into __io_queue_sqe(), more clearly separating responsibilities. BTW, it may need adding extra io_sq_thread_drop_mm() either way > >> /* >> * Drop cur_mm before scheduling, we can't hold it for >> * long periods (or over schedule()). Do this before >> @@ -6152,8 +6159,6 @@ static int io_sq_thread(void *data) >> if (!list_empty(&ctx->poll_list) || >> (!time_after(jiffies, timeout) && ret != -EBUSY && >> !percpu_ref_is_dying(&ctx->refs))) { >> - if (current->task_works) >> - task_work_run(); >> cond_resched(); >> continue; >> } >> @@ -6185,11 +6190,7 @@ static int io_sq_thread(void *data) >> finish_wait(&ctx->sqo_wait, &wait); >> break; >> } >> - if (current->task_works) { >> - task_work_run(); >> - finish_wait(&ctx->sqo_wait, &wait); >> - continue; >> - } >> + >> if (signal_pending(current)) >> flush_signals(current); >> schedule(); >> > -- Pavel Begunkov