+ /*
+ * spin_unlock_wait() is not a memory barriers, it is only a
+ * control barrier. The code must pair with spin_unlock(&sem->lock),
+ * thus just the control barrier is insufficient.
+ *
+ * smp_rmb() is sufficient, as writes cannot pass the control barrier.
+ */
+ smp_rmb();
+}
+
+/*
+ * Try to leave the mode that disallows simple operations:
+ * Caller must own sem_perm.lock.
+ */
+static void complexmode_tryleave(struct sem_array *sma)
+{
+ if (sma->complex_count) {
+ /* Complex ops are sleeping.
+ * We must stay in complex mode
+ */
+ return;
+ }
+ /*
+ * Immediately after setting complex_mode to false,
+ * a simple op can start. Thus: all memory writes
+ * performed by the current operation must be visible
+ * before we set complex_mode to false.
+ */
+ smp_store_release(&sma->complex_mode, false);