btrfs: check error value from btrfs_update_inode in tree log

Error injection testing uncovered a case where we ended up with invalid
link counts on an inode.  This happened because we failed to notice an
error when updating the inode while replaying the tree log, and
committed the transaction with an invalid file system.

Fix this by checking the return value of btrfs_update_inode.  This
resolved the link count errors I was seeing, and we already properly
handle passing up the error values in these paths.

CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tree-log.c

@@ -1574,7 +1574,9 @@ static noinline int add_inode_ref(struct btrfs_trans_handle *trans,
 			if (ret)
 				goto out;
 
-			btrfs_update_inode(trans, root, BTRFS_I(inode));
+			ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
+			if (ret)
+				goto out;
 		}
 
 		ref_ptr = (unsigned long)(ref_ptr + ref_struct_size) + namelen;
@@ -1749,7 +1751,9 @@ static noinline int fixup_inode_link_count(struct btrfs_trans_handle *trans,
 
 	if (nlink != inode->i_nlink) {
 		set_nlink(inode, nlink);
-		btrfs_update_inode(trans, root, BTRFS_I(inode));
+		ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
+		if (ret)
+			goto out;
 	}
 	BTRFS_I(inode)->index_cnt = (u64)-1;