Btrfs: don't traverse the ordered operation list repeatedly

btrfs_run_ordered_operations() needn't traverse the ordered operation list
repeatedly, it is because the transaction commiter will invoke it again when
there is no other writer in this transaction, it can ensure that no one can
add new objects into the ordered operation list.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/ordered-data.c

@@ -626,14 +626,10 @@ int btrfs_run_ordered_operations(struct btrfs_root *root, int wait)
 
 	mutex_lock(&root->fs_info->ordered_operations_mutex);
 	spin_lock(&root->fs_info->ordered_extent_lock);
-again:
 	list_splice_init(&root->fs_info->ordered_operations, &splice);
-
 	while (!list_empty(&splice)) {
-
 		btrfs_inode = list_entry(splice.next, struct btrfs_inode,
 				   ordered_operations);
-
 		inode = &btrfs_inode->vfs_inode;
 
 		list_del_init(&btrfs_inode->ordered_operations);
@@ -642,22 +638,20 @@ again:
 		 * the inode may be getting freed (in sys_unlink path).
 		 */
 		inode = igrab(inode);
-
-		if (!wait && inode) {
-			list_add_tail(&BTRFS_I(inode)->ordered_operations,
-			      &root->fs_info->ordered_operations);
-		}
-
 		if (!inode)
 			continue;
+
+		if (!wait)
+			list_add_tail(&BTRFS_I(inode)->ordered_operations,
+				      &root->fs_info->ordered_operations);
 		spin_unlock(&root->fs_info->ordered_extent_lock);
 
 		work = btrfs_alloc_delalloc_work(inode, wait, 1);
 		if (!work) {
+			spin_lock(&root->fs_info->ordered_extent_lock);
 			if (list_empty(&BTRFS_I(inode)->ordered_operations))
 				list_add_tail(&btrfs_inode->ordered_operations,
 					      &splice);
-			spin_lock(&root->fs_info->ordered_extent_lock);
 			list_splice_tail(&splice,
 					 &root->fs_info->ordered_operations);
 			spin_unlock(&root->fs_info->ordered_extent_lock);
@@ -671,9 +665,6 @@ again:
 		cond_resched();
 		spin_lock(&root->fs_info->ordered_extent_lock);
 	}
-	if (wait && !list_empty(&root->fs_info->ordered_operations))
-		goto again;
-
 	spin_unlock(&root->fs_info->ordered_extent_lock);
 out:
 	list_for_each_entry_safe(work, next, &works, list) {