monitor: do not use mb_read/mb_set for suspend_cnt

Clean up monitor_event to just use monitor_suspend/monitor_resume,
using mon->mux_out to protect against incorrect nesting (especially
on startup).

The only remaining case of reading suspend_cnt is in the can_read
callback, which is just advisory and can use qatomic_read.

As an extra benefit, mux_out is now simply protected by mon_lock.
Also, moving the prompt to the beginning of the main loop removes
it from the output in some error cases where QEMU does not actually
start successfully.  It is not a full fix and it would be nice to
also remove the monitor heading, but this is already a small (though
unintentional) improvement.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/monitor/monitor.c b/monitor/monitor.c
index 20e33e28d2..15f97538ef 100644
--- a/monitor/monitor.c
+++ b/monitor/monitor.c
@@ -569,10 +569,15 @@ static void monitor_accept_input(void *opaque)
 {
     Monitor *mon = opaque;
 
-    if (!monitor_is_qmp(mon)) {
+    qemu_mutex_lock(&mon->mon_lock);
+    if (!monitor_is_qmp(mon) && mon->reset_seen) {
         MonitorHMP *hmp_mon = container_of(mon, MonitorHMP, common);
         assert(hmp_mon->rs);
+        readline_restart(hmp_mon->rs);
+        qemu_mutex_unlock(&mon->mon_lock);
         readline_show_prompt(hmp_mon->rs);
+    } else {
+        qemu_mutex_unlock(&mon->mon_lock);
     }
 
     qemu_chr_fe_accept_input(&mon->chr);
@@ -603,7 +608,7 @@ int monitor_can_read(void *opaque)
 {
     Monitor *mon = opaque;
 
-    return !qatomic_mb_read(&mon->suspend_cnt);
+    return !qatomic_read(&mon->suspend_cnt);
 }
 
 void monitor_list_append(Monitor *mon)