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Thu, 04 Feb 2021 03:20:54 -0800 (PST) To: Hao Xu , Jens Axboe Cc: io-uring@vger.kernel.org, Joseph Qi References: <1612364276-26847-1-git-send-email-haoxu@linux.alibaba.com> <1612364276-26847-3-git-send-email-haoxu@linux.alibaba.com> <9b1d9e51-1b92-a651-304d-919693f9fb6f@gmail.com> <3668106c-5e80-50c8-6221-bdfa246c98ae@linux.alibaba.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 2/2] io_uring: don't hold uring_lock when calling io_run_task_work* Message-ID: Date: Thu, 4 Feb 2021 11:17:10 +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: <3668106c-5e80-50c8-6221-bdfa246c98ae@linux.alibaba.com> 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 04/02/2021 03:25, Hao Xu wrote: > 在 2021/2/4 上午12:45, Pavel Begunkov 写道: >> On 03/02/2021 16:35, Pavel Begunkov wrote: >>> On 03/02/2021 14:57, Hao Xu wrote: >>>> This is caused by calling io_run_task_work_sig() to do work under >>>> uring_lock while the caller io_sqe_files_unregister() already held >>>> uring_lock. >>>> we need to check if uring_lock is held by us when doing unlock around >>>> io_run_task_work_sig() since there are code paths down to that place >>>> without uring_lock held. >>> >>> 1. we don't want to allow parallel io_sqe_files_unregister()s >>> happening, it's synchronised by uring_lock atm. Otherwise it's >>> buggy. > Here "since there are code paths down to that place without uring_lock held" I mean code path of io_ring_ctx_free(). I guess it's to the 1/2, but let me outline the problem again: if you have two tasks userspace threads sharing a ring, then they can both and in parallel call syscall:files_unregeister. That's a potential double percpu_ref_kill(&data->refs), or even worse. Same for 2, but racing for the table and refs. >> >> This one should be simple, alike to >> >> if (percpu_refs_is_dying()) >>     return error; // fail *files_unregister(); >> >>> >>> 2. probably same with unregister and submit. >>> >>>> >>>> Reported-by: Abaci >>>> Fixes: 1ffc54220c44 ("io_uring: fix io_sqe_files_unregister() hangs") >>>> Signed-off-by: Hao Xu >>>> --- >>>>   fs/io_uring.c | 19 +++++++++++++------ >>>>   1 file changed, 13 insertions(+), 6 deletions(-) >>>> >>>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>>> index efb6d02fea6f..b093977713ee 100644 >>>> --- a/fs/io_uring.c >>>> +++ b/fs/io_uring.c >>>> @@ -7362,18 +7362,25 @@ static int io_sqe_files_unregister(struct io_ring_ctx *ctx, bool locked) >>>>         /* wait for all refs nodes to complete */ >>>>       flush_delayed_work(&ctx->file_put_work); >>>> +    if (locked) >>>> +        mutex_unlock(&ctx->uring_lock); >>>>       do { >>>>           ret = wait_for_completion_interruptible(&data->done); >>>>           if (!ret) >>>>               break; >>>>           ret = io_run_task_work_sig(); >>>> -        if (ret < 0) { >>>> -            percpu_ref_resurrect(&data->refs); >>>> -            reinit_completion(&data->done); >>>> -            io_sqe_files_set_node(data, backup_node); >>>> -            return ret; >>>> -        } >>>> +        if (ret < 0) >>>> +            break; >>>>       } while (1); >>>> +    if (locked) >>>> +        mutex_lock(&ctx->uring_lock); >>>> + >>>> +    if (ret < 0) { >>>> +        percpu_ref_resurrect(&data->refs); >>>> +        reinit_completion(&data->done); >>>> +        io_sqe_files_set_node(data, backup_node); >>>> +        return ret; >>>> +    } >>>>         __io_sqe_files_unregister(ctx); >>>>       nr_tables = DIV_ROUND_UP(ctx->nr_user_files, IORING_MAX_FILES_TABLE); >>>> >>> >> > -- Pavel Begunkov