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Sat, 02 Jan 2021 11:57:47 -0800 (PST) To: Marcelo Diop-Gonzalez , axboe@kernel.dk Cc: io-uring@vger.kernel.org References: <20201219191521.82029-1-marcelo827@gmail.com> <20201219191521.82029-3-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 2/2] io_uring: flush timeouts that should already have expired Message-ID: Date: Sat, 2 Jan 2021 19:54:19 +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: <20201219191521.82029-3-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: > Right now io_flush_timeouts() checks if the current number of events > is equal to ->timeout.target_seq, but this will miss some timeouts if > there have been more than 1 event added since the last time they were > flushed (possible in io_submit_flush_completions(), for example). Fix > it by recording the starting value of ->cached_cq_overflow - > ->cq_timeouts instead of the target value, so that we can safely > (without overflow problems) compare the number of events that have > happened with the number of events needed to trigger the timeout. > > Signed-off-by: Marcelo Diop-Gonzalez > --- > fs/io_uring.c | 30 +++++++++++++++++++++++------- > 1 file changed, 23 insertions(+), 7 deletions(-) > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index f394bf358022..f62de0cb5fc4 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -444,7 +444,7 @@ struct io_cancel { > struct io_timeout { > struct file *file; > u32 off; > - u32 target_seq; > + u32 start_seq; > struct list_head list; > /* head of the link, used by linked timeouts only */ > struct io_kiocb *head; > @@ -1629,6 +1629,24 @@ static void __io_queue_deferred(struct io_ring_ctx *ctx) > } while (!list_empty(&ctx->defer_list)); > } > > +static inline u32 io_timeout_events_left(struct io_kiocb *req) > +{ > + struct io_ring_ctx *ctx = req->ctx; > + u32 events; > + > + /* > + * events -= req->timeout.start_seq and the comparison between > + * ->timeout.off and events will not overflow because each time > + * ->cq_timeouts is incremented, ->cached_cq_tail is incremented too. > + */ > + > + events = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts); > + events -= req->timeout.start_seq; It looks to me that events before the start_seq subtraction can have got wrapped around start_seq. e.g. 1) you submit a timeout with off=0xff...ff (start_seq=0 for convenience) 2) some time has passed, let @events = 0xff..ff - 1 so the timeout still waits 3) we commit 5 requests at once and call io_commit_cqring() only once for them, so we get @events == 0xff..ff - 1 + 5, i.e. 4 @events == 4 < off == 0xff...ff, so we didn't trigger out timeout even though should have > + if (req->timeout.off > events) > + return req->timeout.off - events; > + return 0; > +} > + > static void io_flush_timeouts(struct io_ring_ctx *ctx) > { > while (!list_empty(&ctx->timeout_list)) { > @@ -1637,8 +1655,7 @@ static void io_flush_timeouts(struct io_ring_ctx *ctx) > > if (io_is_timeout_noseq(req)) > break; > - if (req->timeout.target_seq != ctx->cached_cq_tail > - - atomic_read(&ctx->cq_timeouts)) > + if (io_timeout_events_left(req) > 0) > break; > > list_del_init(&req->timeout.list); > @@ -5785,7 +5802,6 @@ static int io_timeout(struct io_kiocb *req) > struct io_ring_ctx *ctx = req->ctx; > struct io_timeout_data *data = req->async_data; > struct list_head *entry; > - u32 tail, off = req->timeout.off; > > spin_lock_irq(&ctx->completion_lock); > > @@ -5799,8 +5815,8 @@ static int io_timeout(struct io_kiocb *req) > goto add; > } > > - tail = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts); > - req->timeout.target_seq = tail + off; > + req->timeout.start_seq = ctx->cached_cq_tail - > + atomic_read(&ctx->cq_timeouts); > > /* > * Insertion sort, ensuring the first entry in the list is always > @@ -5813,7 +5829,7 @@ static int io_timeout(struct io_kiocb *req) > if (io_is_timeout_noseq(nxt)) > continue; > /* nxt.seq is behind @tail, otherwise would've been completed */ > - if (off >= nxt->timeout.target_seq - tail) > + if (req->timeout.off >= io_timeout_events_left(nxt)) > break; > } > add: > -- Pavel Begunkov