- case UFFD_STATE_RUNNING:
- /*
- * poll() never guarantees that read won't block.
- * userfaults can be waken before they're read().
- */
- if (unlikely(!(file->f_flags & O_NONBLOCK)))
- return EPOLLERR;
- /*
- * lockless access to see if there are pending faults
- * __pollwait last action is the add_wait_queue but
- * the spin_unlock would allow the waitqueue_active to
- * pass above the actual list_add inside
- * add_wait_queue critical section. So use a full
- * memory barrier to serialize the list_add write of
- * add_wait_queue() with the waitqueue_active read
- * below.
- */
- ret = 0;
- smp_mb();
- if (waitqueue_active(&ctx->fault_pending_wqh))
- ret = EPOLLIN;
- else if (waitqueue_active(&ctx->event_wqh))
- ret = EPOLLIN;