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=-18.8 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 7B760C433F5 for ; Sun, 12 Sep 2021 09:04:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 59BEB61209 for ; Sun, 12 Sep 2021 09:04:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233656AbhILJFc (ORCPT ); Sun, 12 Sep 2021 05:05:32 -0400 Received: from out30-132.freemail.mail.aliyun.com ([115.124.30.132]:47567 "EHLO out30-132.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232845AbhILJFc (ORCPT ); Sun, 12 Sep 2021 05:05:32 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R931e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04420;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0Uo24LUX_1631437456; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0Uo24LUX_1631437456) by smtp.aliyun-inc.com(127.0.0.1); Sun, 12 Sep 2021 17:04:16 +0800 Subject: Re: [PATCH 3/4] io-wq: fix worker->refcount when creating worker in work exit To: Jens Axboe Cc: io-uring@vger.kernel.org, Pavel Begunkov , Joseph Qi References: <20210911194052.28063-1-haoxu@linux.alibaba.com> <20210911194052.28063-4-haoxu@linux.alibaba.com> From: Hao Xu Message-ID: Date: Sun, 12 Sep 2021 17:04:15 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: 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 2021/9/12 上午6:13, Jens Axboe 写道: > On 9/11/21 1:40 PM, Hao Xu wrote: >> We may enter the worker creation path from io_worker_exit(), and >> refcount is already zero, which causes definite failure of worker >> creation. >> io_worker_exit >> ref = 0 >> ->io_wqe_dec_running >> ->io_queue_worker_create >> ->io_worker_get failure since ref is 0 >> >> Signed-off-by: Hao Xu >> --- >> fs/io-wq.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/fs/io-wq.c b/fs/io-wq.c >> index 0e1288a549eb..75e79571bdfd 100644 >> --- a/fs/io-wq.c >> +++ b/fs/io-wq.c >> @@ -188,7 +188,9 @@ static void io_worker_exit(struct io_worker *worker) >> list_del_rcu(&worker->all_list); >> acct->nr_workers--; >> preempt_disable(); >> + refcount_set(&worker->ref, 1); >> io_wqe_dec_running(worker); >> + refcount_set(&worker->ref, 0); > > That kind of refcount manipulation is highly suspect. And in fact it > should not be needed, io_worker_exit() clears ->flags before going on > with worker teardown. Hence you can't hit worker creation from > io_wqe_dec_running(). Doesn't see the relationship between worker->flags and the creation. But yes, the creation path does io_worker_get() which causes failure if it's from io_worker_exit(), Now I understand it is more like a feature, isn't it? Anyway, the issue in 4/4 seems still there. Regards, Hao >