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 B34FFC4338F for ; Fri, 20 Aug 2021 10:16:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9786E60F4A for ; Fri, 20 Aug 2021 10:16:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232659AbhHTKRA (ORCPT ); Fri, 20 Aug 2021 06:17:00 -0400 Received: from out30-54.freemail.mail.aliyun.com ([115.124.30.54]:51462 "EHLO out30-54.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232572AbhHTKQ7 (ORCPT ); Fri, 20 Aug 2021 06:16:59 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01424;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=3;SR=0;TI=SMTPD_---0UkL.3PL_1629454580; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0UkL.3PL_1629454580) by smtp.aliyun-inc.com(127.0.0.1); Fri, 20 Aug 2021 18:16:20 +0800 Subject: Re: [PATCH 1/3] io_uring: flush completions for fallbacks To: Pavel Begunkov , Jens Axboe , io-uring@vger.kernel.org References: <8b941516921f72e1a64d58932d671736892d7fff.1629286357.git.asml.silence@gmail.com> <0fcdffe3-024d-2f0f-78f1-938594f68995@gmail.com> From: Hao Xu Message-ID: <459bb482-e9bd-1457-95f9-3251394747c9@linux.alibaba.com> Date: Fri, 20 Aug 2021 18:16:20 +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: <0fcdffe3-024d-2f0f-78f1-938594f68995@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 2021/8/20 下午5:49, Pavel Begunkov 写道: > On 8/20/21 10:21 AM, Hao Xu wrote: >> 在 2021/8/18 下午7:42, Pavel Begunkov 写道: >>> io_fallback_req_func() doesn't expect anyone creating inline >>> completions, and no one currently does that. Teach the function to flush >>> completions preparing for further changes. >>> >>> Signed-off-by: Pavel Begunkov >>> --- >>>   fs/io_uring.c | 5 +++++ >>>   1 file changed, 5 insertions(+) >>> >>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>> index 3da9f1374612..ba087f395507 100644 >>> --- a/fs/io_uring.c >>> +++ b/fs/io_uring.c >>> @@ -1197,6 +1197,11 @@ static void io_fallback_req_func(struct work_struct *work) >>>       percpu_ref_get(&ctx->refs); >>>       llist_for_each_entry_safe(req, tmp, node, io_task_work.fallback_node) >>>           req->io_task_work.func(req); >>> + >>> +    mutex_lock(&ctx->uring_lock); >>> +    if (ctx->submit_state.compl_nr) >>> +        io_submit_flush_completions(ctx); >>> +    mutex_unlock(&ctx->uring_lock); >> why do we protect io_submit_flush_completions() with uring_lock, >> regarding that it is called in original context. Btw, why not >> use ctx_flush_and_put() > > The fallback thing is called from a workqueue not the submitter task > context. See delayed_work and so. > > Regarding locking, it touches struct io_submit_state, and it's protected by > ->uring_lock. In particular we're interested in ->reqs and ->free_list. > FWIW, there is refurbishment going on around submit state, so if proves > useful the locking may change in coming months. > > ctx_flush_and_put() could have been used, but simpler to hand code it > and avoid the (always messy) conditional ref grabbing and locking. I didn't get it, what do you mean 'avoid the (always messy) conditional ref grabbing and locking'? the code here and in ctx_flush_and_put() are same..though I think in ctx_flush_and_put(), there is a problem that compl_nr should also be protected. >