Btrfs: avoid warning bomb of btrfs_invalidate_inodes

So after transaction is aborted, we need to cleanup inode resources by
calling btrfs_invalidate_inodes(), and btrfs_invalidate_inodes() hopes
roots' refs to be zero in old times and sets a WARN_ON(), however, this
is not always true within cleaning up transaction, so we get to detect
transaction abortion and not warn at all.
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>

fs/btrfs/inode.c

@@ -4926,7 +4926,8 @@ void btrfs_invalidate_inodes(struct btrfs_root *root)
 	struct inode *inode;
 	u64 objectid = 0;
 
-	WARN_ON(btrfs_root_refs(&root->root_item) != 0);
+	if (!test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state))
+		WARN_ON(btrfs_root_refs(&root->root_item) != 0);
 
 	spin_lock(&root->inode_lock);
 again: