1 files changed, 10 insertions, 4 deletions
diff --git a/libports/interrupt-operation.c b/libports/interrupt-operation.c
index 943bd4f4..5d4b0b7a 100644
--- a/libports/interrupt-operation.c
+++ b/libports/interrupt-operation.c
@@ -27,12 +27,18 @@ kern_return_t
 ports_S_interrupt_operation (struct port_info *pi,
 			     mach_port_seqno_t seqno)
 {
+  mach_port_seqno_t old;
+
   if (!pi)
     return EOPNOTSUPP;
-  pthread_mutex_lock (&_ports_lock);
-  if (pi->cancel_threshold < seqno)
-    pi->cancel_threshold = seqno;
-  pthread_mutex_unlock (&_ports_lock);
+
+ retry:
+  old = __atomic_load_n (&pi->cancel_threshold, __ATOMIC_SEQ_CST);
+  if (old < seqno
+      && ! __atomic_compare_exchange_n (&pi->cancel_threshold, &old, seqno,
+					0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST))
+	goto retry;
+
   ports_interrupt_rpcs (pi);
   return 0;
 }