/* Then check that the global lock is free */
if (!spin_is_locked(&sma->sem_perm.lock)) {
- /* spin_is_locked() is not a memory barrier */
- smp_mb();
+ /*
+ * The ipc object lock check must be visible on all
+ * cores before rechecking the complex count. Otherwise
+ * we can race with another thread that does:
+ * complex_count++;
+ * spin_unlock(sem_perm.lock);
+ */
+ smp_rmb();
- /* Now repeat the test of complex_count:
+ /*
+ * Now repeat the test of complex_count:
* It can't change anymore until we drop sem->lock.
* Thus: if is now 0, then it will stay 0.
*/