[PATCH 6/8] btrfs: clear BTRFS_ROOT_DEAD_RELOC_TREE before dropping the reloc root

[Josef Bacik <josef@toxicpanda.com>]

Qu put this in place in order to avoid a use after free in
init_reloc_root.  However a previous patch in this series makes the use
after free impossible because at this point we no longer have a
reloc_control set on the fs_info.

So move this to be coupled with clearing the root->reloc_root so we're
consistent with all other operations of the reloc root.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/relocation.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 9c8a4a4b2bde..5bbed0ea26e1 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2291,18 +2291,19 @@ static int clean_dirty_subvols(struct reloc_control *rc)
 
 			list_del_init(&root->reloc_dirty_list);
 			root->reloc_root = NULL;
-			if (reloc_root) {
-
-				ret2 = btrfs_drop_snapshot(reloc_root, NULL, 0, 1);
-				if (ret2 < 0 && !ret)
-					ret = ret2;
-			}
 			/*
 			 * Need barrier to ensure clear_bit() only happens after
 			 * root->reloc_root = NULL. Pairs with have_reloc_root.
 			 */
 			smp_wmb();
 			clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state);
+
+			if (reloc_root) {
+
+				ret2 = btrfs_drop_snapshot(reloc_root, NULL, 0, 1);
+				if (ret2 < 0 && !ret)
+					ret = ret2;
+			}
 			btrfs_put_root(root);
 		} else {
 			/* Orphan reloc tree, just clean it up */
-- 
2.24.1