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Sat, 02 Jan 2021 12:07:08 -0800 (PST) To: Marcelo Diop-Gonzalez , axboe@kernel.dk Cc: io-uring@vger.kernel.org References: <20201219191521.82029-1-marcelo827@gmail.com> <20201219191521.82029-2-marcelo827@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 v2 1/2] io_uring: only increment ->cq_timeouts along with ->cached_cq_tail Message-ID: Date: Sat, 2 Jan 2021 20:03:40 +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: <20201219191521.82029-2-marcelo827@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 19/12/2020 19:15, Marcelo Diop-Gonzalez wrote: > The quantity ->cached_cq_tail - ->cq_timeouts is used to tell how many > non-timeout events have happened, but this subtraction could overflow > if ->cq_timeouts is incremented more times than ->cached_cq_tail. > It's maybe unlikely, but currently this can happen if a timeout event > overflows the cqring, since in that case io_get_cqring() doesn't > increment ->cached_cq_tail, but ->cq_timeouts is incremented by the > caller. Fix it by incrementing ->cq_timeouts inside io_get_cqring(). > > Signed-off-by: Marcelo Diop-Gonzalez > --- > fs/io_uring.c | 14 +++++++------- > 1 file changed, 7 insertions(+), 7 deletions(-) > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index f3690dfdd564..f394bf358022 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -1582,8 +1582,6 @@ static void io_kill_timeout(struct io_kiocb *req) > > ret = hrtimer_try_to_cancel(&io->timer); > if (ret != -1) { > - atomic_set(&req->ctx->cq_timeouts, > - atomic_read(&req->ctx->cq_timeouts) + 1); > list_del_init(&req->timeout.list); > io_cqring_fill_event(req, 0); > io_put_req_deferred(req, 1); > @@ -1664,7 +1662,7 @@ static inline bool io_sqring_full(struct io_ring_ctx *ctx) > return READ_ONCE(r->sq.tail) - ctx->cached_sq_head == r->sq_ring_entries; > } > > -static struct io_uring_cqe *io_get_cqring(struct io_ring_ctx *ctx) > +static struct io_uring_cqe *io_get_cqring(struct io_ring_ctx *ctx, u8 opcode) > { > struct io_rings *rings = ctx->rings; > unsigned tail; > @@ -1679,6 +1677,10 @@ static struct io_uring_cqe *io_get_cqring(struct io_ring_ctx *ctx) > return NULL; > > ctx->cached_cq_tail++; > + if (opcode == IORING_OP_TIMEOUT) > + atomic_set(&ctx->cq_timeouts, > + atomic_read(&ctx->cq_timeouts) + 1); > + Don't think I like it. The function is pretty hot, so wouldn't want that extra burden just for timeouts, which should be cold enough especially with the new timeout CQ waits. Also passing opcode here is awkward and not very great abstraction wise. > return &rings->cqes[tail & ctx->cq_mask]; > } > > @@ -1728,7 +1730,7 @@ static bool io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force, > if (!io_match_task(req, tsk, files)) > continue; > > - cqe = io_get_cqring(ctx); > + cqe = io_get_cqring(ctx, req->opcode); > if (!cqe && !force) > break; > > @@ -1776,7 +1778,7 @@ static void __io_cqring_fill_event(struct io_kiocb *req, long res, long cflags) > * submission (by quite a lot). Increment the overflow count in > * the ring. > */ > - cqe = io_get_cqring(ctx); > + cqe = io_get_cqring(ctx, req->opcode); > if (likely(cqe)) { > WRITE_ONCE(cqe->user_data, req->user_data); > WRITE_ONCE(cqe->res, res); > @@ -5618,8 +5620,6 @@ static enum hrtimer_restart io_timeout_fn(struct hrtimer *timer) > > spin_lock_irqsave(&ctx->completion_lock, flags); > list_del_init(&req->timeout.list); > - atomic_set(&req->ctx->cq_timeouts, > - atomic_read(&req->ctx->cq_timeouts) + 1); > > io_cqring_fill_event(req, -ETIME); > io_commit_cqring(ctx); > -- Pavel Begunkov