From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 28215C433E0 for ; Mon, 15 Jun 2020 15:32:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0C874207D4 for ; Mon, 15 Jun 2020 15:32:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730603AbgFOPch (ORCPT ); Mon, 15 Jun 2020 11:32:37 -0400 Received: from out30-56.freemail.mail.aliyun.com ([115.124.30.56]:59899 "EHLO out30-56.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730595AbgFOPch (ORCPT ); Mon, 15 Jun 2020 11:32:37 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01355;MF=xiaoguang.wang@linux.alibaba.com;NM=1;PH=DS;RN=3;SR=0;TI=SMTPD_---0U.hw2y0_1592235151; Received: from 30.8.168.89(mailfrom:xiaoguang.wang@linux.alibaba.com fp:SMTPD_---0U.hw2y0_1592235151) by smtp.aliyun-inc.com(127.0.0.1); Mon, 15 Jun 2020 23:32:32 +0800 Subject: Re: [PATCH 2/2] io_uring: add memory barrier to synchronize io_kiocb's result and iopoll_completed To: Jens Axboe , io-uring@vger.kernel.org Cc: joseph.qi@linux.alibaba.com References: <20200615092450.3241-1-xiaoguang.wang@linux.alibaba.com> <20200615092450.3241-3-xiaoguang.wang@linux.alibaba.com> <97cfe28d-cbbe-680a-2f4f-8794d4f90728@kernel.dk> From: Xiaoguang Wang Message-ID: Date: Mon, 15 Jun 2020 23:32:31 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <97cfe28d-cbbe-680a-2f4f-8794d4f90728@kernel.dk> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org hi, > On 6/15/20 8:48 AM, Xiaoguang Wang wrote: >> hi, >> >>> On 6/15/20 3:24 AM, Xiaoguang Wang wrote: >>>> In io_complete_rw_iopoll(), stores to io_kiocb's result and iopoll >>>> completed are two independent store operations, to ensure that once >>>> iopoll_completed is ture and then req->result must been perceived by >>>> the cpu executing io_do_iopoll(), proper memory barrier should be used. >>>> >>>> And in io_do_iopoll(), we check whether req->result is EAGAIN, if it is, >>>> we'll need to issue this io request using io-wq again. In order to just >>>> issue a single smp_rmb() on the completion side, move the re-submit work >>>> to io_iopoll_complete(). >>> >>> Did you actually test this one? >> I only run test cases in liburing/test in a vm. >> >>> >>>> @@ -1736,11 +1748,20 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events, >>>> { >>>> struct req_batch rb; >>>> struct io_kiocb *req; >>>> + LIST_HEAD(again); >>>> + >>>> + /* order with ->result store in io_complete_rw_iopoll() */ >>>> + smp_rmb(); >>>> >>>> rb.to_free = rb.need_iter = 0; >>>> while (!list_empty(done)) { >>>> int cflags = 0; >>>> >>>> + if (READ_ONCE(req->result) == -EAGAIN) { >>>> + req->iopoll_completed = 0; >>>> + list_move_tail(&req->list, &again); >>>> + continue; >>>> + } >>>> req = list_first_entry(done, struct io_kiocb, list); >>>> list_del(&req->list); >>>> >>> >>> You're using 'req' here before you initialize it... >> Sorry, next time when I submit patches, I'll construct test cases which >> will cover my codes changes. > > I'm surprised the compiler didn't complain, or that the regular testing > didn't barf on it. I'm also surprised, will try to find the reason. And indeed the iopoll test case failed, but below command displayed nothing: [lege@localhost test]$ sudo ./iopoll Then I considered this test case pass wrongly. dmesg show errors: [ 127.806945] ================================================================== [ 127.806983] BUG: KASAN: use-after-free in io_iopoll_complete+0xbb/0x980 [ 127.806989] Read of size 4 at addr ffff8886e3e98808 by task io_uring-sq/1643 [ 127.806999] CPU: 16 PID: 1643 Comm: io_uring-sq Not tainted 5.7.0+ #501 [ 127.807013] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.1-0-g0551a4be2c-prebuilt.qemu-project.org 04/01/2014 [ 127.807021] Call Trace: [ 127.807040] dump_stack+0x75/0xa0 [ 127.807047] ? io_iopoll_complete+0xbb/0x980 [ 127.807062] print_address_description.constprop.6+0x1a/0x220 [ 127.807086] ? _raw_write_lock_irqsave+0xd0/0xd0 [ 127.807092] ? io_free_req_many.part.79+0x208/0x2a0 [ 127.807107] ? __rcu_read_unlock+0x37/0x200 [ 127.807112] ? io_iopoll_complete+0xbb/0x980 [ 127.807117] ? io_iopoll_complete+0xbb/0x980 [ 127.807122] kasan_report.cold.9+0x1f/0x42 [ 127.807128] ? io_iopoll_complete+0xbb/0x980 [ 127.807133] io_iopoll_complete+0xbb/0x980 [ 127.807138] ? io_timeout_fn+0x140/0x140 [ 127.807150] ? __switch_to+0x2e9/0x5a0 [ 127.807157] io_iopoll_getevents+0x287/0x310 [ 127.807163] ? io_iopoll_complete+0x980/0x980 [ 127.807172] ? finish_wait+0xcb/0xf0 [ 127.807179] io_sq_thread+0x1c1/0x600 [ 127.807185] ? __ia32_sys_io_uring_enter+0x450/0x450 [ 127.807194] ? preempt_count_add+0x77/0xd0 [ 127.807200] ? _raw_spin_lock_irqsave+0x84/0xd0 [ 127.807206] ? _raw_write_lock_irqsave+0xd0/0xd0 [ 127.807210] ? finish_wait+0xf0/0xf0 [ 127.807215] ? preempt_count_sub+0x18/0xc0 [ 127.807224] ? __kthread_parkme+0xaf/0xd0 [ 127.807231] ? __ia32_sys_io_uring_enter+0x450/0x450 [ 127.807235] kthread+0x1e4/0x210 [ 127.807241] ? kthread_create_on_node+0xa0/0xa0 [ 127.807246] ret_from_fork+0x22/0x30 > > Don't think you need a new test case for this, the iopoll test case > should cover it, if you limit the queue depth on the device by > setting /sys/block//queue/nr_requests to 2 or something like > that. Thanks, I'll try later. Regards, Xiaoguang Wang >