scsi_transport_srp: Fix fast_io_fail_tmo=dev_loss_tmo=off behavior

If scsi_remove_host() is called while an rport is in the blocked state
then scsi_remove_host() will only finish if the rport is unblocked
from inside a timer function. Make sure that an rport only enters the
blocked state if a timer will be started that will unblock it. This
avoids that unloading the ib_srp kernel module after having
disconnected the initiator from the target system results in a
deadlock if both the fast_io_fail_tmo and dev_loss_tmo parameters have
been set to "off".

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Reviewed-by: David Dillow <dave@thedillows.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/scsi/scsi_transport_srp.c

@@ -473,7 +473,8 @@ static void __srp_start_tl_fail_timers(struct srp_rport *rport)
 	if (delay > 0)
 		queue_delayed_work(system_long_wq, &rport->reconnect_work,
 				   1UL * delay * HZ);
-	if (srp_rport_set_state(rport, SRP_RPORT_BLOCKED) == 0) {
+	if ((fast_io_fail_tmo >= 0 || dev_loss_tmo >= 0) &&
+	    srp_rport_set_state(rport, SRP_RPORT_BLOCKED) == 0) {
 		pr_debug("%s new state: %d\n", dev_name(&shost->shost_gendev),
 			 rport->state);
 		scsi_target_block(&shost->shost_gendev);