+
+ spin_lock(&ailp->xa_lock);
+
+ /*
+ * Idle if the AIL is empty and we are not racing with a target
+ * update. We check the AIL after we set the task to a sleep
+ * state to guarantee that we either catch an xa_target update
+ * or that a wake_up resets the state to TASK_RUNNING.
+ * Otherwise, we run the risk of sleeping indefinitely.
+ *
+ * The barrier matches the xa_target update in xfs_ail_push().
+ */
+ smp_rmb();
+ if (!xfs_ail_min(ailp) &&
+ ailp->xa_target == ailp->xa_target_prev) {
+ spin_unlock(&ailp->xa_lock);
+ schedule();
+ tout = 0;
+ continue;
+ }
+ spin_unlock(&ailp->xa_lock);
+
+ if (tout)
+ schedule_timeout(msecs_to_jiffies(tout));
+
+ __set_current_state(TASK_RUNNING);