[PATCH 1/5] btrfs: reorder reservation before reloc root selection

[Josef Bacik <josef@toxicpanda.com>]

Since we're not only checking for metadata reservations but also if we
need to throttle our delayed ref generation, reorder
reserve_metadat_bytes() above the select_reloc_root() call in
reserve_metadat_bytes().  The reason we want this is because
select_reloc_root() will mess with the backref cache, and if we're going
to bail we want to be able to cleanly remove this node from the backref
cache and come back along to regenerate it.  Move it up so this is the
first thing we do to make restarting cleaner.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/relocation.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 3ccc126d0df3..df33649c592c 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -3134,6 +3134,14 @@ static int relocate_tree_block(struct btrfs_trans_handle *trans,
 	if (!node)
 		return 0;
 
+	/*
+	 * If we fail here we want to drop our backref_node because we are going
+	 * to start over and regenerate the tree for it.
+	 */
+	ret = reserve_metadata_space(trans, rc, node);
+	if (ret)
+		goto out;
+
 	BUG_ON(node->processed);
 	root = select_one_root(node);
 	if (root == ERR_PTR(-ENOENT)) {
@@ -3141,12 +3149,6 @@ static int relocate_tree_block(struct btrfs_trans_handle *trans,
 		goto out;
 	}
 
-	if (!root || test_bit(BTRFS_ROOT_REF_COWS, &root->state)) {
-		ret = reserve_metadata_space(trans, rc, node);
-		if (ret)
-			goto out;
-	}
-
 	if (root) {
 		if (test_bit(BTRFS_ROOT_REF_COWS, &root->state)) {
 			BUG_ON(node->new_bytenr);
-- 
2.24.1