Re: [Qemu-devel] [PATCH 2/6] monitor: accept chardev input from iothread

[Peter Xu <peterx@redhat.com>]

On Tue, Oct 09, 2018 at 05:12:47PM +0400, Marc-André Lureau wrote:
> Chardev backends may not handle safely IO events from concurrent
> threads. Better to wake up the chardev from the monitor IO thread if
> it's being used as the chardev context.
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  monitor.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/monitor.c b/monitor.c
> index ab60c9f87e..a25514490a 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -4297,6 +4297,13 @@ int monitor_suspend(Monitor *mon)
>      return 0;
>  }
>  
> +static void monitor_accept_input(void *opaque)
> +{
> +    Monitor *mon = opaque;
> +
> +    qemu_chr_fe_accept_input(&mon->chr);
> +}
> +
>  void monitor_resume(Monitor *mon)
>  {
>      if (monitor_is_hmp_non_interactive(mon)) {
> @@ -4310,13 +4317,14 @@ void monitor_resume(Monitor *mon)
>               * let's kick the thread in case it's sleeping.
>               */
>              if (mon->use_io_thread) {
> -                aio_notify(iothread_get_aio_context(mon_iothread));
> +                aio_bh_schedule_oneshot(iothread_get_aio_context(mon_iothread),
> +                                        monitor_accept_input, mon);

Just to make sure: this will definitely cover the previous
aio_notify(), am I right?

Imho some comment would always be nice here because QMPs with
use_io_thread=true seems special anyway.

>              }
>          } else {
>              assert(mon->rs);
>              readline_show_prompt(mon->rs);
> +            monitor_accept_input(mon);
>          }
> -        qemu_chr_fe_accept_input(&mon->chr);

How about the QMP monitors with oob=off?  Will it miss the call?

I would consider caching the aio context into Monitor struct when
monitor init, then call aio_bh_schedule_oneshot() always with the
per-monitor aio cache.  This could unify the code paths too so we keep
the oob special path as less as possible.

>      }
>      trace_monitor_suspend(mon, -1);
>  }
> -- 
> 2.19.0.271.gfe8321ec05
> 

Regards,

-- 
Peter Xu