From 6d155578e0bb7139b9b5ed0b0057276b592b30a4 Mon Sep 17 00:00:00 2001
From: Brian Foster <bfoster@redhat.com>
Date: Thu, 28 Jun 2012 06:52:56 -0400
Subject: [PATCH] --- yaml --- r: 319867 b: refs/heads/master c:
 8375f922aaa6e7a880022529202fb486315568c3 h: refs/heads/master i:   319865:
 5920528189114a749fc312e8ce9e8d23c59b0144   319863:
 fa9c61c4e19975d1e7cd4745e7dc9d4bae710ee7 v: v3

---
 [refs]                        |  2 +-
 trunk/fs/xfs/xfs_trans_ail.c  | 35 ++++++++++++++++++++++++++++++++---
 trunk/fs/xfs/xfs_trans_priv.h |  1 +
 3 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/[refs] b/[refs]
index 12a313001cbb..2c05b3acf803 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 4f59af758f9092bc7b266ca919ce6067170e5172
+refs/heads/master: 8375f922aaa6e7a880022529202fb486315568c3
diff --git a/trunk/fs/xfs/xfs_trans_ail.c b/trunk/fs/xfs/xfs_trans_ail.c
index 9c514483e599..6011ee661339 100644
--- a/trunk/fs/xfs/xfs_trans_ail.c
+++ b/trunk/fs/xfs/xfs_trans_ail.c
@@ -383,6 +383,12 @@ xfsaild_push(
 	}
 
 	spin_lock(&ailp->xa_lock);
+
+	/* barrier matches the xa_target update in xfs_ail_push() */
+	smp_rmb();
+	target = ailp->xa_target;
+	ailp->xa_target_prev = target;
+
 	lip = xfs_trans_ail_cursor_first(ailp, &cur, ailp->xa_last_pushed_lsn);
 	if (!lip) {
 		/*
@@ -397,7 +403,6 @@ xfsaild_push(
 	XFS_STATS_INC(xs_push_ail);
 
 	lsn = lip->li_lsn;
-	target = ailp->xa_target;
 	while ((XFS_LSN_CMP(lip->li_lsn, target) <= 0)) {
 		int	lock_result;
 
@@ -527,8 +532,32 @@ xfsaild(
 			__set_current_state(TASK_KILLABLE);
 		else
 			__set_current_state(TASK_INTERRUPTIBLE);
-		schedule_timeout(tout ?
-				 msecs_to_jiffies(tout) : MAX_SCHEDULE_TIMEOUT);
+
+		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);
 
 		try_to_freeze();
 
diff --git a/trunk/fs/xfs/xfs_trans_priv.h b/trunk/fs/xfs/xfs_trans_priv.h
index fb62377d1cbc..53b7c9b0f8f7 100644
--- a/trunk/fs/xfs/xfs_trans_priv.h
+++ b/trunk/fs/xfs/xfs_trans_priv.h
@@ -67,6 +67,7 @@ struct xfs_ail {
 	struct task_struct	*xa_task;
 	struct list_head	xa_ail;
 	xfs_lsn_t		xa_target;
+	xfs_lsn_t		xa_target_prev;
 	struct list_head	xa_cursors;
 	spinlock_t		xa_lock;
 	xfs_lsn_t		xa_last_pushed_lsn;