Re: [Qemu-devel] [RFC v4 15/27] monitor: let monitor_{suspend|resume} thread safe

[Peter Xu <peterx@redhat.com>]

On Thu, Nov 23, 2017 at 11:23:16AM +0000, Dr. David Alan Gilbert wrote:
> * Peter Xu (peterx@redhat.com) wrote:
> > Monitor code now can be run in more than one thread.  Let the suspend
> > and resume code be thread safe.
> > 
> > Reviewed-by: Fam Zheng <famz@redhat.com>
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> >  monitor.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/monitor.c b/monitor.c
> > index ec03f1b232..30f9cd80de 100644
> > --- a/monitor.c
> > +++ b/monitor.c
> > @@ -4003,7 +4003,7 @@ int monitor_suspend(Monitor *mon)
> >  {
> >      if (!mon->rs)
> >          return -ENOTTY;
> > -    mon->suspend_cnt++;
> > +    atomic_inc(&mon->suspend_cnt);
> >      return 0;
> >  }
> >  
> > @@ -4011,8 +4011,9 @@ void monitor_resume(Monitor *mon)
> >  {
> >      if (!mon->rs)
> >          return;
> > -    if (--mon->suspend_cnt == 0)
> > +    if (atomic_dec_fetch(&mon->suspend_cnt) == 0) {
> >          readline_show_prompt(mon->rs);
> > +    }
> >  }
> >  
> >  static QObject *get_qmp_greeting(void)
> 
> Do you also need to do an atomic_read() in monitor_can_read?
> (I guess the code in monitor_event is ok because it's only the mux
> path, but still it's probably better to use all atomic ops on
> the suspend_cnt variable to be consistent).

Agreed.

-- 
Peter Xu