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=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_1 autolearn=ham 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 7A03DC4338F for ; Fri, 20 Aug 2021 22:07:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5316161183 for ; Fri, 20 Aug 2021 22:07:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231511AbhHTWIH (ORCPT ); Fri, 20 Aug 2021 18:08:07 -0400 Received: from out30-42.freemail.mail.aliyun.com ([115.124.30.42]:55638 "EHLO out30-42.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229760AbhHTWIH (ORCPT ); Fri, 20 Aug 2021 18:08:07 -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=e01e04426;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0UkTFvcD_1629497246; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0UkTFvcD_1629497246) by smtp.aliyun-inc.com(127.0.0.1); Sat, 21 Aug 2021 06:07:27 +0800 Subject: Re: [PATCH for-5.15] io_uring: fix lacking of protection for compl_nr To: Pavel Begunkov , Jens Axboe Cc: io-uring@vger.kernel.org, Joseph Qi References: <20210820184013.195812-1-haoxu@linux.alibaba.com> <4b6d903b-09ec-0fca-fa70-4c6c32a0f5cb@linux.alibaba.com> <68755d6f-8049-463f-f372-0ddc978a963e@gmail.com> From: Hao Xu Message-ID: Date: Sat, 21 Aug 2021 06:07:26 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <68755d6f-8049-463f-f372-0ddc978a963e@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org 在 2021/8/21 上午5:32, Pavel Begunkov 写道: > On 8/20/21 9:39 PM, Hao Xu wrote: >> 在 2021/8/21 上午2:59, Pavel Begunkov 写道: >>> On 8/20/21 7:40 PM, Hao Xu wrote: >>>> coml_nr in ctx_flush_and_put() is not protected by uring_lock, this >>>> may cause problems when accessing it parallelly. >>> >>> Did you hit any problem? It sounds like it should be fine as is: >>> >>> The trick is that it's only responsible to flush requests added >>> during execution of current call to tctx_task_work(), and those >>> naturally synchronised with the current task. All other potentially >>> enqueued requests will be of someone else's responsibility. >>> >>> So, if nobody flushed requests, we're finely in-sync. If we see >>> 0 there, but actually enqueued a request, it means someone >>> actually flushed it after the request had been added. >>> >>> Probably, needs a more formal explanation with happens-before >>> and so. >> I should put more detail in the commit message, the thing is: >> say coml_nr > 0 >> >>   ctx_flush_and put                  other context >>    if (compl_nr)                      get mutex >>                                       coml_nr > 0 >>                                       do flush >>                                           coml_nr = 0 >>                                       release mutex >>         get mutex >>            do flush (*) >>         release mutex >> >> in (*) place, we do a bunch of unnecessary works, moreover, we > > I wouldn't care about overhead, that shouldn't be much > >> call io_cqring_ev_posted() which I think we shouldn't. > > IMHO, users should expect spurious io_cqring_ev_posted(), > though there were some eventfd users complaining before, so > for them we can do > > if (state->nr) { > lock(); > if (state->nr) flush(); > unlock(); > } Agree. > >>>> Fixes: d10299e14aae ("io_uring: inline struct io_comp_state") >>> >>> FWIW, it came much earlier than this commit, IIRC >>> >>> commit 2c32395d8111037ae2cb8cab883e80bcdbb70713 >>> Author: Pavel Begunkov >>> Date:   Sun Feb 28 22:04:53 2021 +0000 >>> >>>      io_uring: fix __tctx_task_work() ctx race >>> >>> >>>> Signed-off-by: Hao Xu >>>> --- >>>>   fs/io_uring.c | 7 +++---- >>>>   1 file changed, 3 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>>> index c755efdac71f..420f8dfa5327 100644 >>>> --- a/fs/io_uring.c >>>> +++ b/fs/io_uring.c >>>> @@ -2003,11 +2003,10 @@ static void ctx_flush_and_put(struct io_ring_ctx *ctx) >>>>   { >>>>       if (!ctx) >>>>           return; >>>> -    if (ctx->submit_state.compl_nr) { >>>> -        mutex_lock(&ctx->uring_lock); >>>> +    mutex_lock(&ctx->uring_lock); >>>> +    if (ctx->submit_state.compl_nr) >>>>           io_submit_flush_completions(ctx); >>>> -        mutex_unlock(&ctx->uring_lock); >>>> -    } >>>> +    mutex_unlock(&ctx->uring_lock); >>>>       percpu_ref_put(&ctx->refs); >>>>   } >>>> >>> >> >