All callers of d_alloc_parallel() must make sure that resulting
in-lookup dentry (if any) will encounter __d_lookup_done() before
the final dput().  d_add_ci() might end up creating in-lookup
dentries; they are fed to d_splice_alias(), which will normally
make sure they meet __d_lookup_done().  However, it is possible
to end up with d_splice_alias() failing with ERR_PTR(-ELOOP)
without having done so.  It takes a corrupted ntfs or case-insensitive
xfs image, but neither should end up with memory corruption...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>