From nobody Sun May 5 18:54:19 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1517483316738848.1630408657886; Thu, 1 Feb 2018 03:08:36 -0800 (PST) Received: from localhost ([::1]:56281 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ehCjI-00083Q-Ss for importer@patchew.org; Thu, 01 Feb 2018 06:08:32 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34614) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ehCiL-0007XB-3k for qemu-devel@nongnu.org; Thu, 01 Feb 2018 06:07:33 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ehCiG-0007Wn-IO for qemu-devel@nongnu.org; Thu, 01 Feb 2018 06:07:33 -0500 Received: from mx1.redhat.com ([209.132.183.28]:36192) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ehCi2-0007S0-Ny; Thu, 01 Feb 2018 06:07:14 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E11BB272A7; Thu, 1 Feb 2018 11:07:13 +0000 (UTC) Received: from localhost (ovpn-117-253.ams2.redhat.com [10.36.117.253]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4497763B89; Thu, 1 Feb 2018 11:07:09 +0000 (UTC) From: Stefan Hajnoczi To: Date: Thu, 1 Feb 2018 11:07:08 +0000 Message-Id: <20180201110708.8080-1-stefanha@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 01 Feb 2018 11:07:13 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH v2] vl: pause vcpus before stopping iothreads X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Fam Zheng , Stefan Hajnoczi , qemu-block@nongnu.org Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Commit dce8921b2baaf95974af8176406881872067adfa ("iothread: Stop threads before main() quits") introduced iothread_stop_all() to avoid the following virtio-scsi assertion failure: assert(blk_get_aio_context(d->conf.blk) =3D=3D s->ctx); Back then the assertion failed because when bdrv_close_all() made d->conf.blk NULL, blk_get_aio_context() returned the global AioContext instead of s->ctx. The same assertion can still fail today when vcpus submit new I/O requests after iothread_stop_all() has moved the BDS to the global AioContext. This patch hardens the iothread_stop_all() approach by pausing vcpus before calling iothread_stop_all(). Note that the assertion failure is a race condition. It is not possible to reproduce it reliably. Signed-off-by: Stefan Hajnoczi --- v2: * Add comment explaining rationale for this ordering and why it's safe. [Kevin] vl.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/vl.c b/vl.c index e517a8d995..b72a9fc6df 100644 --- a/vl.c +++ b/vl.c @@ -4766,10 +4766,18 @@ int main(int argc, char **argv, char **envp) =20 main_loop(); replay_disable_events(); + + /* The ordering of the following is delicate. Stop vcpus to prevent n= ew + * I/O requests being queued by the guest. Then stop IOThreads (this + * includes a drain operation and completes all request processing). = At + * this point emulated devices are still associated with their IOThrea= ds + * (if any) but no longer have any work to do. Only then can we close + * block devices safely because we know there is no more I/O coming. + */ + pause_all_vcpus(); iothread_stop_all(); - - pause_all_vcpus(); bdrv_close_all(); + res_free(); =20 /* vhost-user must be cleaned up before chardevs. */ --=20 2.14.3