[Qemu-devel] [PATCH 6/6] monitor: protect event emission

[Paolo Bonzini <pbonzini@redhat.com>]

Event emission must be protected by a mutex because of access to
the shared rate-limiting state, and to guard against concurrent
monitor "hot-plug" by means of human-monitor-command.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 monitor.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/monitor.c b/monitor.c
index ebc66fb..f7a4ccf 100644
--- a/monitor.c
+++ b/monitor.c
@@ -210,6 +210,9 @@ struct Monitor {
 /* QMP checker flags */
 #define QMP_ACCEPT_UNKNOWNS 1
 
+/* Protects mon_list, monitor_event_state.  */
+static QemuMutex monitor_lock;
+
 static QLIST_HEAD(mon_list, Monitor) mon_list;
 static QLIST_HEAD(mon_fdsets, MonFdset) mon_fdsets;
 static int mon_refcount;
@@ -531,10 +534,11 @@ static const char *monitor_event_names[] = {
 };
 QEMU_BUILD_BUG_ON(ARRAY_SIZE(monitor_event_names) != QEVENT_MAX)
 
-MonitorEventState monitor_event_state[QEVENT_MAX];
+static MonitorEventState monitor_event_state[QEVENT_MAX];
 
 /*
- * Emits the event to every monitor instance
+ * Emits the event to every monitor instance.
+ * Called with monitor_lock held.
  */
 static void
 monitor_protocol_event_emit(MonitorEvent event,
@@ -571,6 +575,7 @@ monitor_protocol_event_queue(MonitorEvent event,
                                        now);
 
     /* Rate limit of 0 indicates no throttling */
+    qemu_mutex_lock(&monitor_lock);
     if (!evstate->rate) {
         monitor_protocol_event_emit(event, data);
         evstate->last = now;
@@ -595,6 +600,7 @@ monitor_protocol_event_queue(MonitorEvent event,
             evstate->last = now;
         }
     }
+    qemu_mutex_unlock(&monitor_lock);
 }
 
 
@@ -612,12 +618,14 @@ static void monitor_protocol_event_handler(void *opaque)
                                          evstate->data,
                                          evstate->last,
                                          now);
+    qemu_mutex_lock(&monitor_lock);
     if (evstate->data) {
         monitor_protocol_event_emit(evstate->event, evstate->data);
         qobject_decref(evstate->data);
         evstate->data = NULL;
     }
     evstate->last = now;
+    qemu_mutex_unlock(&monitor_lock);
 }
 
 
@@ -5040,6 +5048,11 @@ static void monitor_readline_flush(void *opaque)
     monitor_flush(opaque);
 }
 
+static void __attribute__((constructor)) monitor_lock_init(void)
+{
+    qemu_mutex_init(&monitor_lock);
+}
+
 void monitor_init(CharDriverState *chr, int flags)
 {
     static int is_first_init = 1;
@@ -5077,7 +5090,10 @@ void monitor_init(CharDriverState *chr, int flags)
                               monitor_event, mon);
     }
 
+    qemu_mutex_lock(&monitor_lock);
     QLIST_INSERT_HEAD(&mon_list, mon, entry);
+    qemu_mutex_unlock(&monitor_lock);
+
     if (!default_mon || (flags & MONITOR_IS_DEFAULT))
         default_mon = mon;
 }
-- 
1.8.3.1