From patchwork Tue Mar 10 09:14:43 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Longpeng(Mike)" X-Patchwork-Id: 11428881 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 0CD05139A for ; Tue, 10 Mar 2020 09:15:45 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C738420674 for ; Tue, 10 Mar 2020 09:15:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C738420674 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Received: from localhost ([::1]:55826 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jBazH-0005NH-Ua for patchwork-qemu-devel@patchwork.kernel.org; Tue, 10 Mar 2020 05:15:43 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:58487) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jBayk-0004rx-4I for qemu-devel@nongnu.org; Tue, 10 Mar 2020 05:15:11 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jBayi-0002rO-Ib for qemu-devel@nongnu.org; Tue, 10 Mar 2020 05:15:09 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:3268 helo=huawei.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jBayi-0002bP-7C for qemu-devel@nongnu.org; Tue, 10 Mar 2020 05:15:08 -0400 Received: from DGGEMS411-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id 88E969DBF840174FD901; Tue, 10 Mar 2020 17:15:01 +0800 (CST) Received: from DESKTOP-27KDQMV.china.huawei.com (10.173.228.124) by DGGEMS411-HUB.china.huawei.com (10.3.19.211) with Microsoft SMTP Server id 14.3.487.0; Tue, 10 Mar 2020 17:14:54 +0800 From: "Longpeng(Mike)" To: , Subject: [RFC] cpus: avoid get stuck in pause_all_vcpus Date: Tue, 10 Mar 2020 17:14:43 +0800 Message-ID: <20200310091443.1326-1-longpeng2@huawei.com> X-Mailer: git-send-email 2.25.0.windows.1 MIME-Version: 1.0 X-Originating-IP: [10.173.228.124] X-CFilter-Loop: Reflected X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 45.249.212.191 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , "Dr . David Alan Gilbert" , "qemu-devel @ nongnu . org" , arei.gonglei@huawei.com, huangzhichao@huawei.com, Longpeng Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" From: Longpeng We find an issue when repeat reboot in guest during migration, it cause the migration thread never be waken up again.
| | LOCK BQL | ... | main_loop_should_exit | pause_all_vcpus | 1. set all cpus ->stop=true | and then kick | 2. return if all cpus is paused | (by '->stopped == true'), else| 3. qemu_cond_wait [BQL UNLOCK] | |LOCK BQL |... |do_vm_stop | pause_all_vcpus | (A)set all cpus ->stop=true | and then kick | (B)return if all cpus is paused | (by '->stopped == true'), else | (C)qemu_cond_wait [BQL UNLOCK] 4. be waken up and LOCK BQL | (D)be waken up BUT wait for BQL 5. goto 2. | (BQL is still LOCKed) | resume_all_vcpus | 1. set all cpus ->stop=false | and ->stopped=false | ... | BQL UNLOCK | (E)LOCK BQL | (F)goto B. [but stopped is false now!] |Finally, sleep at step 3 forever. Note: This patch is just for discuss this issue, I'm looking forward to your suggestions, thanks! Cc: Peter Maydell Cc: Dr. David Alan Gilbert Cc: qemu-devel@nongnu.org Signed-off-by: Longpeng --- cpus.c | 41 ++++++++++++++++++++++++++++++++++++----- 1 file changed, 36 insertions(+), 5 deletions(-) diff --git a/cpus.c b/cpus.c index b4f8b84..15e8b21 100644 --- a/cpus.c +++ b/cpus.c @@ -1857,10 +1857,30 @@ static bool all_vcpus_paused(void) return true; } +static bool all_vcpus_resumed(void) +{ + CPUState *cpu; + + CPU_FOREACH(cpu) { + if (cpu->stopped) { + return false; + } + } + + return true; +} + void pause_all_vcpus(void) { CPUState *cpu; + /* We need to drop the replay_lock so any vCPU threads woken up + * can finish their replay tasks + */ +retry_unlock: + replay_mutex_unlock(); + +retry_pause: qemu_clock_enable(QEMU_CLOCK_VIRTUAL, false); CPU_FOREACH(cpu) { if (qemu_cpu_is_self(cpu)) { @@ -1871,13 +1891,17 @@ void pause_all_vcpus(void) } } - /* We need to drop the replay_lock so any vCPU threads woken up - * can finish their replay tasks - */ - replay_mutex_unlock(); - while (!all_vcpus_paused()) { qemu_cond_wait(&qemu_pause_cond, &qemu_global_mutex); + /* + * All of the vcpus maybe resumed due to the race with other + * threads that doing pause && resume, and we'll stuck as a + * result. So we need to request again if the race occurs. + */ + if (all_vcpus_resumed()) { + goto retry_pause; + } + CPU_FOREACH(cpu) { qemu_cpu_kick(cpu); } @@ -1886,6 +1910,13 @@ void pause_all_vcpus(void) qemu_mutex_unlock_iothread(); replay_mutex_lock(); qemu_mutex_lock_iothread(); + /* + * The vcpus maybe resumed during the mutex is unlocking, we must + * make sure all of the vcpus are paused before return. + */ + if (!all_vcpus_paused()) { + goto retry_unlock; + } } void cpu_resume(CPUState *cpu)