scsi: lpfc: Fix crash in target side cable pulls hitting WAIT_FOR_UNREG

Kernel is crashing with the following stacktrace:

  BUG: unable to handle kernel NULL pointer dereference at
    00000000000005bc
  IP: lpfc_nvme_register_port+0x1a8/0x3a0 [lpfc]
  ...
  Call Trace:
  lpfc_nlp_state_cleanup+0x2b2/0x500 [lpfc]
  lpfc_nlp_set_state+0xd7/0x1a0 [lpfc]
  lpfc_cmpl_prli_prli_issue+0x1f7/0x450 [lpfc]
  lpfc_disc_state_machine+0x7a/0x1e0 [lpfc]
  lpfc_cmpl_els_prli+0x16f/0x1e0 [lpfc]
  lpfc_sli_sp_handle_rspiocb+0x5b2/0x690 [lpfc]
  lpfc_sli_handle_slow_ring_event_s4+0x182/0x230 [lpfc]
  lpfc_do_work+0x87f/0x1570 [lpfc]
  kthread+0x10d/0x130
  ret_from_fork+0x35/0x40

During target side fault injections, it is possible to hit the
NLP_WAIT_FOR_UNREG case in lpfc_nvme_remoteport_delete. A prior commit
fixed a rebind and delete race condition, but called lpfc_nlp_put
unconditionally. This triggered a deletion and the crash.

Fix by movng nlp_put to inside the NLP_WAIT_FOR_UNREG case, where the nlp
will be being unregistered/removed. Leave the reference if the flag isn't
set.

Link: https://lore.kernel.org/r/20200322181304.37655-8-jsmart2021@gmail.com
Fixes: b15bd3e ("scsi: lpfc: Fix nvme remoteport registration race conditions")
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/lpfc/lpfc_nvme.c

@@ -382,13 +382,15 @@ lpfc_nvme_remoteport_delete(struct nvme_fc_remote_port *remoteport)
 	if (ndlp->upcall_flags & NLP_WAIT_FOR_UNREG) {
 		ndlp->nrport = NULL;
 		ndlp->upcall_flags &= ~NLP_WAIT_FOR_UNREG;
-	}
-	spin_unlock_irq(&vport->phba->hbalock);
+		spin_unlock_irq(&vport->phba->hbalock);
 
-	/* Remove original register reference. The host transport
-	 * won't reference this rport/remoteport any further.
-	 */
-	lpfc_nlp_put(ndlp);
+		/* Remove original register reference. The host transport
+		 * won't reference this rport/remoteport any further.
+		 */
+		lpfc_nlp_put(ndlp);
+	} else {
+		spin_unlock_irq(&vport->phba->hbalock);
+	}
 
  rport_err:
 	return;