trace: Lock vCPU list when initializing dynamic tracing state

Fixes potential corruption when a vCPU is hot-(un)plugged while
initializing the current one.

Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
Message-id: 148278747515.1404.6538173443841279200.stgit@fimbulvetr.bsc.es
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

trace/control-target.c

@@ -79,7 +79,7 @@ void trace_event_set_vcpu_state_dynamic(CPUState *vcpu,
     }
 }
 
-static bool adding_first_cpu(void)
+static bool adding_first_cpu1(void)
 {
     CPUState *cpu;
     size_t count = 0;
@@ -92,6 +92,15 @@ static bool adding_first_cpu(void)
     return true;
 }
 
+static bool adding_first_cpu(void)
+{
+    bool res;
+    cpu_list_lock();
+    res = adding_first_cpu1();
+    cpu_list_unlock();
+    return res;
+}
+
 void trace_init_vcpu(CPUState *vcpu)
 {
     TraceEventIter iter;