KVM: Prevent trace call into unloaded module text

Add marker_synchronize_unregister() before module unloading.
This prevents possible trace calls into unloaded module text.
Signed-off-by: Wu Fengguang <wfg@linux.intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

virt/kvm/kvm_trace.c

@@ -252,6 +252,7 @@ void kvm_trace_cleanup(void)
 			struct kvm_trace_probe *p = &kvm_trace_probes[i];
 			marker_probe_unregister(p->name, p->probe_func, p);
 		}
+		marker_synchronize_unregister();
 
 		relay_close(kt->rchan);
 		debugfs_remove(kt->lost_file);