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Sat, 20 Feb 2021 06:36:56 -0800 (PST) Subject: Re: [PATCH 2/3] io_uring: fix io_rsrc_ref_quiesce races From: Pavel Begunkov To: Hao Xu , Jens Axboe , io-uring@vger.kernel.org References: <1b71f4059f088b035ec72307321f051a7be2d44f.1613767375.git.asml.silence@gmail.com> <070f2274-187d-8ee8-e841-f44beeba4fd0@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== Message-ID: Date: Sat, 20 Feb 2021 14:33:06 +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: <070f2274-187d-8ee8-e841-f44beeba4fd0@gmail.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 20/02/2021 14:07, Pavel Begunkov wrote: > On 20/02/2021 06:31, Hao Xu wrote: >> 在 2021/2/20 上午4:45, Pavel Begunkov 写道: >>> There are different types of races in io_rsrc_ref_quiesce()  between >>> ->release() of percpu_refs and reinit_completion(), fix them by always >>> resurrecting between iterations. BTW, clean the function up, because >>> DRY. >>> >>> Fixes: 0ce4a72632317 ("io_uring: don't hold uring_lock when calling io_run_task_work*") >>> Signed-off-by: Pavel Begunkov >>> --- >>> -        /* >>> -         * There is small possibility that data->done is already completed >>> -         * So reinit it here >>> -         */ >>> +        percpu_ref_resurrect(&data->refs); >> I've thought about this, if we resurrect data->refs, then we can't >> avoid parallel files unregister by percpu_refs_is_dying. > > Right, totally forgot about it, but otherwise we race with data->done. > Didn't test yet, but a diff below should do the trick. > >>> +        if (ret < 0) >>> +            return ret; >>> +        backup_node = alloc_fixed_rsrc_ref_node(ctx); >>> +        if (!backup_node) >>> +            return -ENOMEM; >> Should we resurrect data->refs and reinit completion before >> signal or error return? > > Not sure what exactly you mean, we should not release uring_lock with > inconsistent state, so it's done right before unlock. And we should not > do it before wait_for_completion_interruptible() before it would take a > reference. > >>> +        init_fixed_file_ref_node(ctx, backup_node); >>> +    } while (1); >>>         destroy_fixed_rsrc_ref_node(backup_node); >>>       return 0; upd diff --git a/fs/io_uring.c b/fs/io_uring.c index ce5fccf00367..12796de8ad10 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -236,6 +236,7 @@ struct fixed_rsrc_data { struct fixed_rsrc_ref_node *node; struct percpu_ref refs; struct completion done; + bool quiesce; }; struct io_buffer { @@ -7335,10 +7336,12 @@ static int io_rsrc_ref_quiesce(struct fixed_rsrc_data *data, struct fixed_rsrc_ref_node *backup_node; int ret; + data->quiesce = true; do { backup_node = alloc_fixed_rsrc_ref_node(ctx); + ret = -ENOMEM; if (!backup_node) - return -ENOMEM; + break; backup_node->rsrc_data = data; backup_node->rsrc_put = rsrc_put; @@ -7353,16 +7356,17 @@ static int io_rsrc_ref_quiesce(struct fixed_rsrc_data *data, percpu_ref_resurrect(&data->refs); synchronize_rcu(); io_sqe_rsrc_set_node(ctx, data, backup_node); + backup_node = NULL; reinit_completion(&data->done); mutex_unlock(&ctx->uring_lock); ret = io_run_task_work_sig(); mutex_lock(&ctx->uring_lock); - if (ret < 0) - return ret; - } while (1); + } while (ret >= 0); - destroy_fixed_rsrc_ref_node(backup_node); - return 0; + data->quiesce = false; + if (backup_node) + destroy_fixed_rsrc_ref_node(backup_node); + return ret; } static struct fixed_rsrc_data *alloc_fixed_rsrc_data(struct io_ring_ctx *ctx) @@ -7401,7 +7405,7 @@ static int io_sqe_files_unregister(struct io_ring_ctx *ctx) * Since we possibly drop uring lock later in this function to * run task work. */ - if (!data || percpu_ref_is_dying(&data->refs)) + if (!data || data->quiesce) return -ENXIO; ret = io_rsrc_ref_quiesce(data, ctx, io_ring_file_put); if (ret) -- Pavel Begunkov