From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34430) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fQGie-0007zG-Ln for qemu-devel@nongnu.org; Tue, 05 Jun 2018 14:30:10 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fQGib-0004Sm-Fs for qemu-devel@nongnu.org; Tue, 05 Jun 2018 14:30:08 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54062) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fQGib-0004RD-1o for qemu-devel@nongnu.org; Tue, 05 Jun 2018 14:30:05 -0400 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.24]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id ABA7181DF4 for ; Tue, 5 Jun 2018 18:30:03 +0000 (UTC) Date: Tue, 5 Jun 2018 15:30:01 -0300 From: Eduardo Habkost Message-ID: <20180605183001.GO7451@localhost.localdomain> References: <1528207243-268226-1-git-send-email-imammedo@redhat.com> <1528207243-268226-3-git-send-email-imammedo@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <1528207243-268226-3-git-send-email-imammedo@redhat.com> 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 Cc: qemu-devel@nongnu.org, berrange@redhat.com, mreitz@redhat.com, pbonzini@redhat.com, ldoktor@redhat.com On Tue, Jun 05, 2018 at 04:00:43PM +0200, 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=E9 > 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; > int fd =3D 0; > =20 > + if (os_setup_post_done) { > + return; > + } > + os_setup_post_done =3D true; > + This part is nice because it allows the os_setup_post() call in the second main loop to be unconditional, but: > if (daemonize) { > if (chdir("/")) { > error_report("not able to chdir to /: %s", strerror(errno)= ); > diff --git a/vl.c b/vl.c > index fa44138..d6fa67f 100644 > --- a/vl.c > +++ b/vl.c > @@ -1960,6 +1960,7 @@ static void main_loop(void) > #ifdef CONFIG_PROFILER > ti =3D profile_getclock(); > #endif > + os_setup_post(); > main_loop_wait(false); Ensuring the correctness of this os_setup_post() call depends on reading the whole body of main_loop_should_exit(), which is a complex and large function. I think this is too fragile for my taste. I prefer Daniel's approach where we have two os_setup_post()/main_loop() call sites, and the first one is conditional on --preconfig. > #ifdef CONFIG_PROFILER > dev_time +=3D profile_getclock() - ti; > @@ -4707,7 +4708,6 @@ int main(int argc, char **argv, char **envp) > } > =20 > accel_setup_post(current_machine); > - os_setup_post(); > =20 > main_loop(); > =20 > --=20 > 2.7.4 >=20 --=20 Eduardo