When we reach monitor_qmp_setup_handlers_bh() we must be using the
IOThread then, so no need to check against it any more.  Instead, we
assert.

Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 monitor.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/monitor.c b/monitor.c
index 77861e96af..5cd9398824 100644
--- a/monitor.c
+++ b/monitor.c
@@ -4624,15 +4624,10 @@ static void monitor_qmp_setup_handlers_bh(void *opaque)
     Monitor *mon = opaque;
     GMainContext *context;
 
-    if (mon->use_io_thread) {
-        /* Use @mon_iothread context */
-        context = monitor_get_io_context();
-        assert(context);
-    } else {
-        /* Use default main loop context */
-        context = NULL;
-    }
-
+    assert(mon->use_io_thread);
+    /* Use @mon_iothread context */
+    context = monitor_get_io_context();
+    assert(context);
     qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read, monitor_qmp_read,
                              monitor_qmp_event, NULL, mon, context, true);
     monitor_list_append(mon);
-- 
2.17.1

Hi

On Wed, Aug 15, 2018 at 3:37 PM, Peter Xu <peterx@redhat.com> wrote:
> When we reach monitor_qmp_setup_handlers_bh() we must be using the
> IOThread then, so no need to check against it any more.  Instead, we
> assert.
>
> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>

That's a clear simplification that I also found, so ack in principle.

However, I don't understand the need of a BH in the first place.
monitor_get_io_context() will return the iothread associated context.
Could you explain?
thanks


> ---
>  monitor.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
>
> diff --git a/monitor.c b/monitor.c
> index 77861e96af..5cd9398824 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -4624,15 +4624,10 @@ static void monitor_qmp_setup_handlers_bh(void *opaque)
>      Monitor *mon = opaque;
>      GMainContext *context;
>
> -    if (mon->use_io_thread) {
> -        /* Use @mon_iothread context */
> -        context = monitor_get_io_context();
> -        assert(context);
> -    } else {
> -        /* Use default main loop context */
> -        context = NULL;
> -    }
> -
> +    assert(mon->use_io_thread);
> +    /* Use @mon_iothread context */
> +    context = monitor_get_io_context();
> +    assert(context);
>      qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read, monitor_qmp_read,
>                               monitor_qmp_event, NULL, mon, context, true);
>      monitor_list_append(mon);
> --
> 2.17.1
>

On Tue, Aug 21, 2018 at 08:13:59PM +0200, Marc-André Lureau wrote:
> Hi
> 
> On Wed, Aug 15, 2018 at 3:37 PM, Peter Xu <peterx@redhat.com> wrote:
> > When we reach monitor_qmp_setup_handlers_bh() we must be using the
> > IOThread then, so no need to check against it any more.  Instead, we
> > assert.
> >
> > Reviewed-by: Markus Armbruster <armbru@redhat.com>
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> 
> That's a clear simplification that I also found, so ack in principle.
> 
> However, I don't understand the need of a BH in the first place.
> monitor_get_io_context() will return the iothread associated context.
> Could you explain?
> thanks

Please refer to the comment in monitor_init():

        /*
        * We can't call qemu_chr_fe_set_handlers() directly here
        * since chardev might be running in the monitor I/O
        * thread.  Schedule a bottom half.
        */
        aio_bh_schedule_oneshot(monitor_get_aio_context(),
                                monitor_qmp_setup_handlers_bh, mon);

To be more specific: in qemu_chr_fe_set_handlers() after we call
qemu_chr_be_update_read_handlers() then the iothread might already
have started to operate on the chardev, so it can race with
qemu_chr_fe_set_handlers() itself if we call it directly in the main
thread.

Regards,

-- 
Peter Xu

Peter Xu <peterx@redhat.com> writes:

> When we reach monitor_qmp_setup_handlers_bh() we must be using the
> IOThread then, so no need to check against it any more.  Instead, we
> assert.
>
> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  monitor.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
>
> diff --git a/monitor.c b/monitor.c
> index 77861e96af..5cd9398824 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -4624,15 +4624,10 @@ static void monitor_qmp_setup_handlers_bh(void *opaque)
>      Monitor *mon = opaque;
>      GMainContext *context;
>  
> -    if (mon->use_io_thread) {
> -        /* Use @mon_iothread context */
> -        context = monitor_get_io_context();
> -        assert(context);
> -    } else {
> -        /* Use default main loop context */
> -        context = NULL;
> -    }
> -
> +    assert(mon->use_io_thread);
> +    /* Use @mon_iothread context */

Mind if I drop this comment?

> +    context = monitor_get_io_context();
> +    assert(context);
>      qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read, monitor_qmp_read,
>                               monitor_qmp_event, NULL, mon, context, true);
>      monitor_list_append(mon);

R-by stands, of course.

On Mon, Aug 27, 2018 at 01:29:29PM +0200, Markus Armbruster wrote:
> > @@ -4624,15 +4624,10 @@ static void monitor_qmp_setup_handlers_bh(void *opaque)
> >      Monitor *mon = opaque;
> >      GMainContext *context;
> >  
> > -    if (mon->use_io_thread) {
> > -        /* Use @mon_iothread context */
> > -        context = monitor_get_io_context();
> > -        assert(context);
> > -    } else {
> > -        /* Use default main loop context */
> > -        context = NULL;
> > -    }
> > -
> > +    assert(mon->use_io_thread);
> > +    /* Use @mon_iothread context */
> 
> Mind if I drop this comment?

Yes, please.

> 
> > +    context = monitor_get_io_context();
> > +    assert(context);
> >      qemu_chr_fe_set_handlers(&mon->chr, monitor_can_read, monitor_qmp_read,
> >                               monitor_qmp_event, NULL, mon, context, true);
> >      monitor_list_append(mon);
> 
> R-by stands, of course.

Regards,

-- 
Peter Xu