[PATCH 2/8] btrfs: do not init a reloc root if we aren't relocating

[Josef Bacik <josef@toxicpanda.com>]

We previously were checking if the root had a dead root before accessing
root->reloc_root in order to avoid a UAF type bug.  However this
scenario happens after we've unset the reloc control, so we would have
been saved if we'd simply checked for fs_info->reloc_control.  At this
point during relocation we no longer need to be creating new reloc
roots, so simply move this check above the reloc_root checks to avoid
any future races and confusion.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/relocation.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 507361e99316..2141519a9dd0 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1527,6 +1527,10 @@ int btrfs_init_reloc_root(struct btrfs_trans_handle *trans,
 	int clear_rsv = 0;
 	int ret;
 
+	if (!rc || !rc->create_reloc_tree ||
+	    root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
+		return 0;
+
 	/*
 	 * The subvolume has reloc tree but the swap is finished, no need to
 	 * create/update the dead reloc tree
@@ -1540,10 +1544,6 @@ int btrfs_init_reloc_root(struct btrfs_trans_handle *trans,
 		return 0;
 	}
 
-	if (!rc || !rc->create_reloc_tree ||
-	    root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
-		return 0;
-
 	if (!trans->reloc_reserved) {
 		rsv = trans->block_rsv;
 		trans->block_rsv = rc->block_rsv;
-- 
2.24.1