This test is checking the wrong variable.  It should be testing "res".
The "sdeb_zbc_model" variable is an enum (unsigned in this situation)
and we never assign negative values to it.
[mkp: fixed commit desc issue reported by Doug]
Link: https://lore.kernel.org/r/20200509100408.GA5555@mwanda
Fixes: 9267e0eb41fe ("scsi: scsi_debug: Add ZBC module parameter")
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
 
                res = sysfs_match_string(zbc_model_strs_b, cp);
                if (res < 0) {
                        res = sysfs_match_string(zbc_model_strs_c, cp);
-                       if (sdeb_zbc_model < 0)
+                       if (res < 0)
                                return -EINVAL;
                }
        }