[PATCH 4/5] btrfs: walk waited ordered roots in place

Like the previous change for btrfs_wait_ordered_extents(), walk
fs_info->ordered_roots in place instead of splicing it onto a private list,
so the roots with pending ordered extents stay visible while we wait.

No functional change intended.

Signed-off-by: Johannes Thumshirn <[email protected]>
---
 fs/btrfs/ordered-data.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index 11aa7e8efe04..ddd21aa5c640 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -836,19 +836,22 @@ void btrfs_wait_ordered_roots(struct btrfs_fs_info *fs_info, u64 nr,
 			      const struct btrfs_block_group *bg)
 {
 	struct btrfs_root *root;
-	LIST_HEAD(splice);
 	u64 done;
+	u64 remaining;
 
 	mutex_lock(&fs_info->ordered_operations_mutex);
 	spin_lock(&fs_info->ordered_root_lock);
-	list_splice_init(&fs_info->ordered_roots, &splice);
-	while (!list_empty(&splice) && nr) {
-		root = list_first_entry(&splice, struct btrfs_root,
-					ordered_root);
+	remaining = 0;
+	list_for_each_entry(root, &fs_info->ordered_roots, ordered_root)
+		remaining++;
+	while (remaining && nr && !list_empty(&fs_info->ordered_roots)) {
+		remaining--;
+		root = list_first_entry(&fs_info->ordered_roots,
+					struct btrfs_root, ordered_root);
+		list_move_tail(&root->ordered_root, &fs_info->ordered_roots);
 		root = btrfs_grab_root(root);
-		BUG_ON(!root);
-		list_move_tail(&root->ordered_root,
-			       &fs_info->ordered_roots);
+		if (!root)
+			continue;
 		spin_unlock(&fs_info->ordered_root_lock);
 
 		done = btrfs_wait_ordered_extents(root, nr, bg);
@@ -859,7 +862,6 @@ void btrfs_wait_ordered_roots(struct btrfs_fs_info *fs_info, u64 nr,
 
 		spin_lock(&fs_info->ordered_root_lock);
 	}
-	list_splice_tail(&splice, &fs_info->ordered_roots);
 	spin_unlock(&fs_info->ordered_root_lock);
 	mutex_unlock(&fs_info->ordered_operations_mutex);
 }
-- 
2.54.0