From patchwork Wed Dec 15 12:29:21 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: "D. Wythe" X-Patchwork-Id: 12678229 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id ADCCDC4332F for ; Wed, 15 Dec 2021 12:29:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242500AbhLOM30 (ORCPT ); Wed, 15 Dec 2021 07:29:26 -0500 Received: from out30-42.freemail.mail.aliyun.com ([115.124.30.42]:40515 "EHLO out30-42.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242428AbhLOM3Z (ORCPT ); Wed, 15 Dec 2021 07:29:25 -0500 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=e01e04423;MF=alibuda@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0V-j2cWu_1639571363; Received: from localhost(mailfrom:alibuda@linux.alibaba.com fp:SMTPD_---0V-j2cWu_1639571363) by smtp.aliyun-inc.com(127.0.0.1); Wed, 15 Dec 2021 20:29:23 +0800 From: "D. Wythe" To: kgraul@linux.ibm.com Cc: kuba@kernel.org, davem@davemloft.net, netdev@vger.kernel.org, linux-s390@vger.kernel.org, linux-rdma@vger.kernel.org, "D. Wythe" Subject: [PATCH net] net/smc: Prevent smc_release() from long blocking Date: Wed, 15 Dec 2021 20:29:21 +0800 Message-Id: <1639571361-101128-1-git-send-email-alibuda@linux.alibaba.com> X-Mailer: git-send-email 1.8.3.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org From: "D. Wythe" In nginx/wrk benchmark, there's a hung problem with high probability on case likes that: (client will last several minutes to exit) server: smc_run nginx client: smc_run wrk -c 10000 -t 1 http://server Client hangs with the following backtrace: 0 [ffffa7ce8Of3bbf8] __schedule at ffffffff9f9eOd5f 1 [ffffa7ce8Of3bc88] schedule at ffffffff9f9eløe6 2 [ffffa7ce8Of3bcaO] schedule_timeout at ffffffff9f9e3f3c 3 [ffffa7ce8Of3bd2O] wait_for_common at ffffffff9f9el9de 4 [ffffa7ce8Of3bd8O] __flush_work at ffffffff9fOfeOl3 5 [ffffa7ce8øf3bdfO] smc_release at ffffffffcO697d24 [smc] 6 [ffffa7ce8Of3be2O] __sock_release at ffffffff9f8O2e2d 7 [ffffa7ce8Of3be4ø] sock_close at ffffffff9f8ø2ebl 8 [ffffa7ce8øf3be48] __fput at ffffffff9f334f93 9 [ffffa7ce8Of3be78] task_work_run at ffffffff9flOlff5 10 [ffffa7ce8Of3beaO] do_exit at ffffffff9fOe5Ol2 11 [ffffa7ce8Of3bflO] do_group_exit at ffffffff9fOe592a 12 [ffffa7ce8Of3bf38] __x64_sys_exit_group at ffffffff9fOe5994 13 [ffffa7ce8Of3bf4O] do_syscall_64 at ffffffff9f9d4373 14 [ffffa7ce8Of3bfsO] entry_SYSCALL_64_after_hwframe at ffffffff9fa0007c This issue dues to flush_work(), which is used to wait for smc_connect_work() to finish in smc_release(). Once lots of smc_connect_work() was pending or all executing work dangling, smc_release() has to block until one worker comes to free, which is equivalent to wait another smc_connnect_work() to finish. In order to fix this, There are two changes: 1. For those idle smc_connect_work(), cancel it from the workqueue; for executing smc_connect_work(), waiting for it to finish. For that purpose, replace flush_work() with cancel_work_sync(). 2. Since smc_connect() hold a reference for passive closing, if smc_connect_work() has been cancelled, release the reference. Fixes: 24ac3a08e658 ("smc: rebuild nonblocking connect") Reported-by: Tony Lu Tested-by: Dust Li Reviewed-by: Dust Li Reviewed-by: Tony Lu Signed-off-by: D. Wythe Acked-by: Karsten Graul --- net/smc/af_smc.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c index b44cc4c..5d9911c 100644 --- a/net/smc/af_smc.c +++ b/net/smc/af_smc.c @@ -195,7 +195,9 @@ static int smc_release(struct socket *sock) /* cleanup for a dangling non-blocking connect */ if (smc->connect_nonblock && sk->sk_state == SMC_INIT) tcp_abort(smc->clcsock->sk, ECONNABORTED); - flush_work(&smc->connect_work); + + if (cancel_work_sync(&smc->connect_work)) + sock_put(&smc->sk); /* sock_hold in smc_connect for passive closing */ if (sk->sk_state == SMC_LISTEN) /* smc_close_non_accepted() is called and acquires