btrfs: add missing error handling when logging operation while COWing extent buffer

When COWing an extent buffer that is not the root node, we need to log in
the tree mod log that we replaced a pointer in the parent node, otherwise
a tree mod log user doing a search on the b+tree can return incorrect
results (that miss something). We are doing the call to
btrfs_tree_mod_log_insert_key() but we totally ignore its return value.

So fix this by adding the missing error handling, resulting in a
transaction abort and freeing the COWed extent buffer.

Fixes: f230475e ("Btrfs: put all block modifications into the tree mod log")
CC: stable@vger.kernel.org # 5.4+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.c

@@ -595,8 +595,14 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
 		add_root_to_dirty_list(root);
 	} else {
 		WARN_ON(trans->transid != btrfs_header_generation(parent));
-		btrfs_tree_mod_log_insert_key(parent, parent_slot,
-					      BTRFS_MOD_LOG_KEY_REPLACE);
+		ret = btrfs_tree_mod_log_insert_key(parent, parent_slot,
+						    BTRFS_MOD_LOG_KEY_REPLACE);
+		if (ret) {
+			btrfs_tree_unlock(cow);
+			free_extent_buffer(cow);
+			btrfs_abort_transaction(trans, ret);
+			return ret;
+		}
 		btrfs_set_node_blockptr(parent, parent_slot,
 					cow->start);
 		btrfs_set_node_ptr_generation(parent, parent_slot,