+ /*
+ * When a thread stops operating on an address space, the loop
+ * in membarrier_private_expedited() may not observe that
+ * tsk->mm, and the loop in membarrier_global_expedited() may
+ * not observe a MEMBARRIER_STATE_GLOBAL_EXPEDITED
+ * rq->membarrier_state, so those would not issue an IPI.
+ * Membarrier requires a memory barrier after accessing
+ * user-space memory, before clearing tsk->mm or the
+ * rq->membarrier_state.
+ */
+ smp_mb__after_spinlock();
+ local_irq_disable();