After the conditional that precedes the following code, inode may be an
ERR_PTR value. This can eg result from a memory allocation failure via the
call to btrfs_iget, and thus does not imply that root is different than
sub_root. Thus, an IS_ERR check is added to ensure that there is no
dereference of inode in this case.
The semantic match that finds this problem is as follows:
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