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Mon, 22 Feb 2021 05:50:08 -0800 (PST) Subject: Re: [PATCH 01/18] io_uring: remove the need for relying on an io-wq fallback worker To: Jens Axboe , io-uring@vger.kernel.org Cc: ebiederm@xmission.com, viro@zeniv.linux.org.uk, torvalds@linux-foundation.org References: <20210219171010.281878-1-axboe@kernel.dk> <20210219171010.281878-2-axboe@kernel.dk> 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== Message-ID: Date: Mon, 22 Feb 2021 13:46:19 +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: <20210219171010.281878-2-axboe@kernel.dk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 19/02/2021 17:09, Jens Axboe wrote: > We hit this case when the task is exiting, and we need somewhere to > do background cleanup of requests. Instead of relying on the io-wq > task manager to do this work for us, just stuff it somewhere where > we can safely run it ourselves directly. > > Signed-off-by: Jens Axboe > --- > fs/io-wq.c | 12 ------------ > fs/io-wq.h | 2 -- > fs/io_uring.c | 38 +++++++++++++++++++++++++++++++++++--- > 3 files changed, 35 insertions(+), 17 deletions(-) > > diff --git a/fs/io-wq.c b/fs/io-wq.c > index c36bbcd823ce..800b299f9772 100644 > --- a/fs/io-wq.c > +++ b/fs/io-wq.c > @@ -16,7 +16,6 @@ > #include > #include > #include > -#include > #include > #include > #include > @@ -775,9 +774,6 @@ static int io_wq_manager(void *data) > complete(&wq->done); > > while (!kthread_should_stop()) { > - if (current->task_works) > - task_work_run(); > - > for_each_node(node) { > struct io_wqe *wqe = wq->wqes[node]; > bool fork_worker[2] = { false, false }; > @@ -800,9 +796,6 @@ static int io_wq_manager(void *data) > schedule_timeout(HZ); > } > > - if (current->task_works) > - task_work_run(); > - > out: > if (refcount_dec_and_test(&wq->refs)) { > complete(&wq->done); > @@ -1160,11 +1153,6 @@ void io_wq_destroy(struct io_wq *wq) > __io_wq_destroy(wq); > } > > -struct task_struct *io_wq_get_task(struct io_wq *wq) > -{ > - return wq->manager; > -} > - > static bool io_wq_worker_affinity(struct io_worker *worker, void *data) > { > struct task_struct *task = worker->task; > diff --git a/fs/io-wq.h b/fs/io-wq.h > index 096f1021018e..a1610702f222 100644 > --- a/fs/io-wq.h > +++ b/fs/io-wq.h > @@ -124,8 +124,6 @@ typedef bool (work_cancel_fn)(struct io_wq_work *, void *); > enum io_wq_cancel io_wq_cancel_cb(struct io_wq *wq, work_cancel_fn *cancel, > void *data, bool cancel_all); > > -struct task_struct *io_wq_get_task(struct io_wq *wq); > - > #if defined(CONFIG_IO_WQ) > extern void io_wq_worker_sleeping(struct task_struct *); > extern void io_wq_worker_running(struct task_struct *); > diff --git a/fs/io_uring.c b/fs/io_uring.c > index d951acb95117..bbd1ec7aa9e9 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -455,6 +455,9 @@ struct io_ring_ctx { > > struct io_restriction restrictions; > > + /* exit task_work */ > + struct callback_head *exit_task_work; > + > /* Keep this last, we don't need it for the fast path */ > struct work_struct exit_work; > }; > @@ -2313,11 +2316,14 @@ static int io_req_task_work_add(struct io_kiocb *req) > static void io_req_task_work_add_fallback(struct io_kiocb *req, > task_work_func_t cb) > { > - struct task_struct *tsk = io_wq_get_task(req->ctx->io_wq); > + struct io_ring_ctx *ctx = req->ctx; > + struct callback_head *head; > > init_task_work(&req->task_work, cb); > - task_work_add(tsk, &req->task_work, TWA_NONE); > - wake_up_process(tsk); > + do { > + head = ctx->exit_task_work; > + req->task_work.next = head; > + } while (cmpxchg(&ctx->exit_task_work, head, &req->task_work) != head); > } > > static void __io_req_task_cancel(struct io_kiocb *req, int error) > @@ -9258,6 +9264,30 @@ void __io_uring_task_cancel(void) > io_uring_remove_task_files(tctx); > } > > +static void io_run_ctx_fallback(struct io_ring_ctx *ctx) > +{ > + struct callback_head *work, *head, *next; > + > + do { > + do { > + head = NULL; > + work = READ_ONCE(ctx->exit_task_work); > + if (!work) > + break; > + } while (cmpxchg(&ctx->exit_task_work, work, head) != work); Looking at io_uring-worker.v3, it's actually just xchg() without do-while. work = xchg(&ctx->exit_task_work, NULL); > + > + if (!work) > + break; > + > + do { > + next = work->next; > + work->func(work); > + work = next; > + cond_resched(); > + } while (work); > + } while (1); > +} > + > static int io_uring_flush(struct file *file, void *data) > { > struct io_uring_task *tctx = current->io_uring; > @@ -9268,6 +9298,8 @@ static int io_uring_flush(struct file *file, void *data) > io_req_caches_free(ctx, current); > } > > + io_run_ctx_fallback(ctx); > + > if (!tctx) > return 0; > > -- Pavel Begunkov