From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33380) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fQDeS-0007c0-91 for qemu-devel@nongnu.org; Tue, 05 Jun 2018 11:13:37 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fQDeP-0002C4-4b for qemu-devel@nongnu.org; Tue, 05 Jun 2018 11:13:36 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:49380 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fQDeO-0002Bd-W3 for qemu-devel@nongnu.org; Tue, 05 Jun 2018 11:13:33 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 55C5F805A530 for ; Tue, 5 Jun 2018 15:13:32 +0000 (UTC) References: <1528207243-268226-1-git-send-email-imammedo@redhat.com> <1528207243-268226-3-git-send-email-imammedo@redhat.com> From: Eric Blake Message-ID: Date: Tue, 5 Jun 2018 10:13:30 -0500 MIME-Version: 1.0 In-Reply-To: <1528207243-268226-3-git-send-email-imammedo@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v3 2/2] vl: fix use of --daemonize with --preconfig List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Igor Mammedov , qemu-devel@nongnu.org Cc: ldoktor@redhat.com, pbonzini@redhat.com, ehabkost@redhat.com, mreitz@redhat.com On 06/05/2018 09:00 AM, Igor Mammedov wrote: > When using --daemonize, the initial lead process will fork a child and > then wait to be notified that setup is complete via a pipe, before it > exits. When using --preconfig there is an extra call to main_loop() > before the notification is done from os_setup_post(). Thus the parent > process won't exit until the mgmt application connects to the monitor > and tells QEMU to leave the RUN_STATE_PRECONFIG. The mgmt application > won't connect to the monitor until daemonizing has completed though. >=20 > This is a chicken and egg problem, leading to deadlock at startup. >=20 > The only viable way to fix this is to call os_setup_post() before > the early main_loop_wait() call when in RUN_STATE_PRECONFIG. This has > the downside that any errors from this point onwards won't be handled > well by the mgmt application, because it will think QEMU has started > successfully, so not be expecting an abrupt exit. The only way to > deal with that is to move as much user input validation as possible > to before the main_loop() call. This is left as an exercise for > future interested developers. >=20 > Based on: > From: Daniel P. Berrang=C3=A9 > Subject: [PATCH v2 2/2] vl: fix use of --daemonize with --preconfig > Message-Id: <20180604120345.12955-3-berrange@redhat.com> >=20 > Signed-off-by: Igor Mammedov > --- > v3: > - rewrite to apply on top of 1/2 > --- > os-posix.c | 6 ++++++ > vl.c | 2 +- > 2 files changed, 7 insertions(+), 1 deletion(-) >=20 > diff --git a/os-posix.c b/os-posix.c > index 9ce6f74..ee06a8d 100644 > --- a/os-posix.c > +++ b/os-posix.c > @@ -309,8 +309,14 @@ void os_daemonize(void) > =20 > void os_setup_post(void) > { > + static bool os_setup_post_done =3D false; The '=3D false' is not technically necessary; all static variables defaul= t=20 to zero-initialization. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org