From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41779) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fPnv3-0005QA-Gf for qemu-devel@nongnu.org; Mon, 04 Jun 2018 07:45:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fPnuy-0001iw-Hi for qemu-devel@nongnu.org; Mon, 04 Jun 2018 07:45:01 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:55156 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 1fPnuy-0001iV-Af for qemu-devel@nongnu.org; Mon, 04 Jun 2018 07:44:56 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6EE65854E2 for ; Mon, 4 Jun 2018 11:44:54 +0000 (UTC) Date: Mon, 4 Jun 2018 13:44:52 +0200 From: Igor Mammedov Message-ID: <20180604134452.7479eb1f@redhat.com> In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] cli: Don't run early event loop if no --preconfig was specified List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Michal Privoznik Cc: qemu-devel@nongnu.org, ehabkost@redhat.com, pbonzini@redhat.com On Sat, 2 Jun 2018 12:34:52 +0200 Michal Privoznik wrote: > After 047f7038f586d215 it is possible for event loop to run two > times. First time whilst parsing command line options (the idea > is to bring up monitor early so that management applications can > tweak config before machine is initialized). And the second time > is after everything is set up (this is the usual place). In both > cases the event loop is called as main_loop_wait(nonblocking = > false) which causes the event loop to block until at least one > event occurred. > > Now, consider that somebody (i.e. libvirt) calls us with > -daemonize. This operation is split in two steps. The main() > calls os_daemonize() which fork()-s and then waits in read() > until child notifies it via write(): > > /qemu.git $ ./x86_64-softmmu/qemu-system-x86_64 -S -daemonize \ > -no-user-config -nodefaults -nographic > > main(): child: > os_daemonize(): > read(pipe[0]) > > main_loop(): > main_loop_wait(false) > > os_setup_post(): > write(pipe[1]) > > main_loop(): > main_loop_wait(false) > > Here it can be clearly seen that main() does not exit until an > event occurs, but at the same time nobody will touch the monitor > socket until their exec("qemu-system-*") finishes. So the whole > thing deadlocks. > > The solution is to not call main_loop() unless --preconfig was > specified (in which case caller knows they must connect to the > socket before exec() finishes). > > Signed-off-by: Michal Privoznik Reviewed-by: Igor Mammedov > --- > vl.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/vl.c b/vl.c > index 70f090c823..cde2934c40 100644 > --- a/vl.c > +++ b/vl.c > @@ -4469,8 +4469,13 @@ int main(int argc, char **argv, char **envp) > } > parse_numa_opts(current_machine); > > - /* do monitor/qmp handling at preconfig state if requested */ > - main_loop(); > + if (preconfig_exit_requested) { > + runstate_set(RUN_STATE_PRELAUNCH); > + preconfig_exit_requested = false; > + } else { > + /* do monitor/qmp handling at preconfig state if requested */ > + main_loop(); > + } > > /* from here on runstate is RUN_STATE_PRELAUNCH */ > machine_run_board_init(current_machine);