Btrfs: update backrefs while dropping snapshot

The new backref format has restriction on type of backref item.  If a tree
block isn't referenced by its owner tree, full backrefs must be used for the
pointers in it. When a tree block loses its owner tree's reference, backrefs
for the pointers in it should be updated to full backrefs. Current
btrfs_drop_snapshot misses the code that updates backrefs, so it's unsafe for
general use.

This patch adds backrefs update code to btrfs_drop_snapshot.  It isn't a
problem in the restricted form btrfs_drop_snapshot is used today, but for
general snapshot deletion this update is required.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 1 insertions, 4 deletions

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index b23dc209ae10..008397934778 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1788,7 +1788,7 @@ static void merge_func(struct btrfs_work *work)
                 btrfs_end_transaction(trans, root);
         }
 
-        btrfs_drop_dead_root(reloc_root);
+        btrfs_drop_snapshot(reloc_root, 0);
 
         if (atomic_dec_and_test(async->num_pending))
                 complete(async->done);
@@ -2075,9 +2075,6 @@ static int do_relocation(struct btrfs_trans_handle *trans,
 
                         ret = btrfs_drop_subtree(trans, root, eb, upper->eb);
                         BUG_ON(ret);
-
-                        btrfs_tree_unlock(eb);
-                        free_extent_buffer(eb);
                 }
                 if (!lowest) {
                         btrfs_tree_unlock(upper->eb);