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. > > This is a chicken and egg problem, leading to deadlock at startup. > > 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. > > Based on: > From: Daniel P. Berrangé <berra...@redhat.com> > Subject: [PATCH v2 2/2] vl: fix use of --daemonize with --preconfig > Message-Id: <20180604120345.12955-3-berra...@redhat.com> > > Signed-off-by: Igor Mammedov <imamm...@redhat.com> > --- > v3: > - rewrite to apply on top of 1/2 > --- > os-posix.c | 6 ++++++ > vl.c | 2 +- > 2 files changed, 7 insertions(+), 1 deletion(-) > > 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) > > void os_setup_post(void) > { > + static bool os_setup_post_done = false; > int fd = 0; > > + if (os_setup_post_done) { > + return; > + } > + os_setup_post_done = 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 = 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 += profile_getclock() - ti; > @@ -4707,7 +4708,6 @@ int main(int argc, char **argv, char **envp) > } > > accel_setup_post(current_machine); > - os_setup_post(); > > main_loop(); > > -- > 2.7.4 > -- Eduardo