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Sun, 07 Feb 2021 09:33:46 -0800 (PST) To: Xiaoguang Wang , io-uring@vger.kernel.org Cc: axboe@kernel.dk, joseph.qi@linux.alibaba.com References: <20210206150006.1945-1-xiaoguang.wang@linux.alibaba.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] io_uring: don't issue reqs in iopoll mode when ctx is dying Message-ID: Date: Sun, 7 Feb 2021 17:30:01 +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: <20210206150006.1945-1-xiaoguang.wang@linux.alibaba.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 06/02/2021 15:00, Xiaoguang Wang wrote: > Abaci Robot reported following panic: > ------------[ cut here ]------------ > refcount_t: underflow; use-after-free. > WARNING: CPU: 1 PID: 195 at lib/refcount.c:28 refcount_warn_saturate+0x137/0x140 > Modules linked in: > CPU: 1 PID: 195 Comm: kworker/u4:2 Not tainted 5.11.0-rc3+ #70 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.1-0-g0551a4be2c-prebuilt.qemu-project.or4 > Workqueue: events_unbound io_ring_exit_work > RIP: 0010:refcount_warn_saturate+0x137/0x140 > Code: 05 ad 63 49 08 01 e8 45 0f 6f 00 0f 0b e9 16 ff ff ff e8 4c ba ae ff 48 c7 c7 28 2e 7c 82 c6 05 90 63 40 > RSP: 0018:ffffc900002e3cc8 EFLAGS: 00010282 > RAX: 0000000000000000 RBX: 0000000000000003 RCX: 0000000000000000 > RDX: ffff888102918000 RSI: ffffffff81150a34 RDI: ffff88813bd28570 > RBP: ffff8881075cd348 R08: 0000000000000001 R09: 0000000000000001 > R10: 0000000000000001 R11: 0000000000080000 R12: ffff8881075cd308 > R13: ffff8881075cd348 R14: ffff888122d33ab8 R15: ffff888104780300 > FS: 0000000000000000(0000) GS:ffff88813bd00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000108 CR3: 0000000107636005 CR4: 0000000000060ee0 > Call Trace: > io_dismantle_req+0x3f3/0x5b0 > __io_free_req+0x2c/0x270 > io_put_req+0x4c/0x70 > io_wq_cancel_cb+0x171/0x470 > ? io_match_task.part.0+0x80/0x80 > __io_uring_cancel_task_requests+0xa0/0x190 > io_ring_exit_work+0x32/0x3e0 > process_one_work+0x2f3/0x720 > worker_thread+0x5a/0x4b0 > ? process_one_work+0x720/0x720 > kthread+0x138/0x180 > ? kthread_park+0xd0/0xd0 > ret_from_fork+0x1f/0x30 > > Later system will panic for some memory corruption. > > The io_identity's count is underflowed. It's because in io_put_identity, > first argument tctx comes from req->task->io_uring, the second argument > comes from the task context that calls io_req_init_async, so the compare > in io_put_identity maybe meaningless. See below case: > task context A issue one polled req, then req->task = A. > task context B do iopoll, above req returns with EAGAIN error. > task context B re-issue req, call io_queue_async_work for req. > req->task->io_uring will set to task context B's identity, or cow new one. > then for above case, in io_put_identity(), the compare is meaningless. > > IIUC, req->task should indicates the initial task context that issues req, > then if it gets EAGAIN error, we'll call io_prep_async_work() in req->task > context, but iopoll reqs seems special, they maybe issued successfully and > got re-issued in other task context because of EAGAIN error. Looks as you say, but the patch doesn't solve the issue completely. 1. We must not do io_queue_async_work() under a different task context, because of it potentially uses a different set of resources. So, I just thought that it would be better to punt it to the right task context via task_work. But... 2. ...iovec import from io_resubmit_prep() might happen after submit ends, i.e. when iovec was freed in userspace. And that's not great at all. > Currently for this panic, we can disable issuing reqs that are returned > with EAGAIN error in iopoll mode when ctx is dying, but we may need to > re-consider the io identity codes more. > > Reported-by: Abaci Robot > Signed-off-by: Xiaoguang Wang > --- > fs/io_uring.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index 9db05171a774..e3b90426d72b 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -2467,7 +2467,12 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events, > int cflags = 0; > > req = list_first_entry(done, struct io_kiocb, inflight_entry); > - if (READ_ONCE(req->result) == -EAGAIN) { > + /* > + * If ctx is dying, don't need to issue reqs that are returned > + * with EAGAIN error, since there maybe no users to reap them. > + */ > + if ((READ_ONCE(req->result) == -EAGAIN) && > + !percpu_ref_is_dying(&ctx->refs)) { > req->result = 0; > req->iopoll_completed = 0; > list_move_tail(&req->inflight_entry, &again); > -- Pavel Begunkov