scsi: scsi_dh: Don't look for NULL devices handlers by name

Currently scsi_dh_lookup() doesn't check for NULL as a device name. This
combined with nvme over dm-mpath results in the following messages
emitted by device-mapper:

 device-mapper: multipath: Could not failover device 259:67: Handler scsi_dh_(null) error 14.

Let scsi_dh_lookup() fail fast on NULL names.

[mkp: typo fix]

Cc: <stable@vger.kernel.org> # v4.16
Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/scsi/scsi_dh.c b/drivers/scsi/scsi_dh.c
index b88b5dbbc444..188f30572aa1 100644
--- a/drivers/scsi/scsi_dh.c
+++ b/drivers/scsi/scsi_dh.c
@@ -112,6 +112,9 @@ static struct scsi_device_handler *scsi_dh_lookup(const char *name)
 {
         struct scsi_device_handler *dh;
 
+        if (!name || strlen(name) == 0)
+                return NULL;
+
         dh = __scsi_dh_lookup(name);
         if (!dh) {
                 request_module("scsi_dh_%s", name);