init_waitqueue_head(bit_wait_table + i);
}
#endif /* ! HAVE_WAIT_VAR_EVENT */
+
+#ifndef HAVE_WAIT_WOKEN
+/*
+ * DEFINE_WAIT_FUNC(wait, woken_wake_func);
+ *
+ * add_wait_queue(&wq_head, &wait);
+ * for (;;) {
+ * if (condition)
+ * break;
+ *
+ * // in wait_woken() // in woken_wake_function()
+ *
+ * p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN;
+ * smp_mb(); // A try_to_wake_up():
+ * if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier>
+ * schedule() if (p->state & mode)
+ * p->state = TASK_RUNNING; p->state = TASK_RUNNING;
+ * wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~
+ * smp_mb(); // B condition = true;
+ * } smp_mb(); // C
+ * remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN;
+ */
+long wait_woken(struct wait_queue_entry *wq_entry, unsigned int mode,
+ long timeout)
+{
+ /*
+ * The below executes an smp_mb(), which matches with the full barrier
+ * executed by the try_to_wake_up() in woken_wake_function() such that
+ * either we see the store to wq_entry->flags in woken_wake_function()
+ * or woken_wake_function() sees our store to current->state.
+ */
+ set_current_state(mode); /* A */
+ if (!(wq_entry->flags & WQ_FLAG_WOKEN))
+ timeout = schedule_timeout(timeout);
+ __set_current_state(TASK_RUNNING);
+
+ /*
+ * The below executes an smp_mb(), which matches with the smp_mb() (C)
+ * in woken_wake_function() such that either we see the wait condition
+ * being true or the store to wq_entry->flags in woken_wake_function()
+ * follows ours in the coherence order.
+ */
+ smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
+
+ return timeout;
+}
+EXPORT_SYMBOL(wait_woken);
+
+int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned int mode,
+ int sync, void *key)
+{
+ /* Pairs with the smp_store_mb() in wait_woken(). */
+ smp_mb(); /* C */
+ wq_entry->flags |= WQ_FLAG_WOKEN;
+
+ return default_wake_function(wq_entry, mode, sync, key);
+}
+EXPORT_SYMBOL(woken_wake_function);
+#endif /* HAVE_WAIT_WOKEN */