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Sat, 20 Feb 2021 06:10:55 -0800 (PST) To: Hao Xu , Jens Axboe , io-uring@vger.kernel.org References: <1b71f4059f088b035ec72307321f051a7be2d44f.1613767375.git.asml.silence@gmail.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 2/3] io_uring: fix io_rsrc_ref_quiesce races Message-ID: <070f2274-187d-8ee8-e841-f44beeba4fd0@gmail.com> Date: Sat, 20 Feb 2021 14:07:05 +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 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 >> --- >>   fs/io_uring.c | 46 +++++++++++++--------------------------------- >>   1 file changed, 13 insertions(+), 33 deletions(-) >> >> diff --git a/fs/io_uring.c b/fs/io_uring.c >> index 50d4dba08f82..38ed52065a29 100644 >> --- a/fs/io_uring.c >> +++ b/fs/io_uring.c >> @@ -7316,19 +7316,6 @@ static void io_sqe_rsrc_set_node(struct io_ring_ctx *ctx, >>       percpu_ref_get(&rsrc_data->refs); >>   } >>   -static int io_sqe_rsrc_add_node(struct io_ring_ctx *ctx, struct fixed_rsrc_data *data) >> -{ >> -    struct fixed_rsrc_ref_node *backup_node; >> - >> -    backup_node = alloc_fixed_rsrc_ref_node(ctx); >> -    if (!backup_node) >> -        return -ENOMEM; >> -    init_fixed_file_ref_node(ctx, backup_node); >> -    io_sqe_rsrc_set_node(ctx, data, backup_node); >> - >> -    return 0; >> -} >> - >>   static void io_sqe_rsrc_kill_node(struct io_ring_ctx *ctx, struct fixed_rsrc_data *data) >>   { >>       struct fixed_rsrc_ref_node *ref_node = NULL; >> @@ -7347,36 +7334,29 @@ static int io_rsrc_ref_quiesce(struct fixed_rsrc_data *data, >>   { >>       int ret; >>   -    io_sqe_rsrc_kill_node(ctx, data); >> -    percpu_ref_kill(&data->refs); >> - >> -    /* wait for all refs nodes to complete */ >> -    flush_delayed_work(&ctx->rsrc_put_work); >>       do { >> +        io_sqe_rsrc_kill_node(ctx, data); >> +        percpu_ref_kill(&data->refs); >> +        flush_delayed_work(&ctx->rsrc_put_work); >> + >>           ret = wait_for_completion_interruptible(&data->done); >>           if (!ret) >>               break; >>   -        ret = io_sqe_rsrc_add_node(ctx, data); >> -        if (ret < 0) >> -            break; >> -        /* >> -         * 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; >> > diff --git a/fs/io_uring.c b/fs/io_uring.c index ce5fccf00367..0af1572634de 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 { @@ -7335,6 +7336,7 @@ 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); if (!backup_node) @@ -7353,16 +7355,19 @@ 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 +7406,7 @@ 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)