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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_GIT 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 DBCF9C433ED for ; Wed, 21 Apr 2021 15:19:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 966546144B for ; Wed, 21 Apr 2021 15:19:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235474AbhDUPTx (ORCPT ); Wed, 21 Apr 2021 11:19:53 -0400 Received: from out30-133.freemail.mail.aliyun.com ([115.124.30.133]:49106 "EHLO out30-133.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234573AbhDUPTw (ORCPT ); Wed, 21 Apr 2021 11:19:52 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R641e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04400;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0UWJQea-_1619018351; Received: from e18g09479.et15sqa.tbsite.net(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0UWJQea-_1619018351) by smtp.aliyun-inc.com(127.0.0.1); Wed, 21 Apr 2021 23:19:18 +0800 From: Hao Xu To: Jens Axboe Cc: io-uring@vger.kernel.org, Pavel Begunkov , Joseph Qi Subject: [PATCH] io_uring: check sqring and iopoll_list before shedule Date: Wed, 21 Apr 2021 23:19:11 +0800 Message-Id: <1619018351-75883-1-git-send-email-haoxu@linux.alibaba.com> X-Mailer: git-send-email 1.8.3.1 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org do this to avoid race below: userspace kernel | check sqring and iopoll_list submit sqe | check IORING_SQ_NEED_WAKEUP | (which is not set) | | | set IORING_SQ_NEED_WAKEUP wait cqe | schedule(never wakeup again) Signed-off-by: Hao Xu --- Hi all, I'm doing some work to reduce cpu usage in low IO pression, and I removed timeout logic in io_sq_thread() to do some test with fio-3.26, I found that fio hangs in getevents, inifinitely trying to get a cqe, While sq-thread is sleeping. It seems there is race situation, and it is still there even after I fix the issue described above in the commit message. I doubt it is something to do with memory barrier logic between userspace and kernel, I'm trying to address it, not many clues for now. I'll send the fio config and kernel modification I did for test in following mail soon. Thanks, Hao fs/io_uring.c | 36 +++++++++++++++++++----------------- 1 file changed, 19 insertions(+), 17 deletions(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index dff34975d86b..042f1149db51 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -6802,27 +6802,29 @@ static int io_sq_thread(void *data) continue; } - needs_sched = true; prepare_to_wait(&sqd->wait, &wait, TASK_INTERRUPTIBLE); - list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) { - if ((ctx->flags & IORING_SETUP_IOPOLL) && - !list_empty_careful(&ctx->iopoll_list)) { - needs_sched = false; - break; - } - if (io_sqring_entries(ctx)) { - needs_sched = false; - break; - } - } - - if (needs_sched && !test_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state)) { + if (!test_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state)) { list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) io_ring_set_wakeup_flag(ctx); - mutex_unlock(&sqd->lock); - schedule(); - mutex_lock(&sqd->lock); + needs_sched = true; + list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) { + if ((ctx->flags & IORING_SETUP_IOPOLL) && + !list_empty_careful(&ctx->iopoll_list)) { + needs_sched = false; + break; + } + if (io_sqring_entries(ctx)) { + needs_sched = false; + break; + } + } + + if (needs_sched) { + mutex_unlock(&sqd->lock); + schedule(); + mutex_lock(&sqd->lock); + } list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) io_ring_clear_wakeup_flag(ctx); } -- 1.8.3.1