scsi: scsi_transport_srp: Sanitize scsi_target_block/unblock sequences

The SCSI midlayer does not allow state transitions from SDEV_BLOCK to
SDEV_BLOCK so calling scsi_target_block() from __rport_fast_io_fail() is
wrong as the port is already blocked.  Similarly, we don't need to call
scsi_target_unblock() afterwards as the function has already done this.

Link: https://lore.kernel.org/r/20200728134833.42547-1-hare@suse.deReviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_transport_srp.c

@@ -395,6 +395,10 @@ static void srp_reconnect_work(struct work_struct *work)
 	}
 }
 
+/*
+ * scsi_target_block() must have been called before this function is
+ * called to guarantee that no .queuecommand() calls are in progress.
+ */
 static void __rport_fail_io_fast(struct srp_rport *rport)
 {
 	struct Scsi_Host *shost = rport_to_shost(rport);
@@ -404,11 +408,7 @@ static void __rport_fail_io_fast(struct srp_rport *rport)
 
 	if (srp_rport_set_state(rport, SRP_RPORT_FAIL_FAST))
 		return;
-	/*
-	 * Call scsi_target_block() to wait for ongoing shost->queuecommand()
-	 * calls before invoking i->f->terminate_rport_io().
-	 */
-	scsi_target_block(rport->dev.parent);
+
 	scsi_target_unblock(rport->dev.parent, SDEV_TRANSPORT_OFFLINE);
 
 	/* Involve the LLD if possible to terminate all I/O on the rport. */
@@ -570,8 +570,6 @@ int srp_reconnect_rport(struct srp_rport *rport)
 		 * failure timers if these had not yet been started.
 		 */
 		__rport_fail_io_fast(rport);
-		scsi_target_unblock(&shost->shost_gendev,
-				    SDEV_TRANSPORT_OFFLINE);
 		__srp_start_tl_fail_timers(rport);
 	} else if (rport->state != SRP_RPORT_BLOCKED) {
 		scsi_target_unblock(&shost->shost_gendev,