scsi: lpfc: Fix RSCN timeout due to incorrect gidft counter

In configs with a large number of initiators in the same zone (>250), RSCN
timeouts are seen when creating or deleting vports:

   lpfc 0000:07:00.1: 5:(0):0231 RSCN timeout Data: x0 x3

During RSCN processing driver issues GID_FT command to nameserver. A
counter for number of simultaneous GID_FT commands is maintained (an
unsigned value). The counter is incremented when the GID_FT is issued.  If
the GID_FT command fails for some reason the driver retries the GID_FT from
the completion call back. But the counter was decremented before the retry
was issued.  When the second GID_FT completes, the callback again tries to
decrement the counter, possibly wrapping to a very large non-zero value,
which causes the RSCN cleanup code to not execute. Thus the RSCN timeout
failure.

Do not decrement the counter on a retry. Also add defensive checks to
ensure the counter is not decremented if already zero.

Link: https://lore.kernel.org/r/20200803210229.23063-4-jsmart2021@gmail.com
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: Dick Kennedy

drivers/scsi/lpfc/lpfc_ct.c

@@ -713,7 +713,8 @@ lpfc_cmpl_ct_cmd_gid_ft(struct lpfc_hba *phba, struct lpfc_iocbq *cmdiocb,
 		/* This is a GID_FT completing so the gidft_inp counter was
 		 * incremented before the GID_FT was issued to the wire.
 		 */
-		vport->gidft_inp--;
+		if (vport->gidft_inp)
+			vport->gidft_inp--;
 
 		/*
 		 * Skip processing the NS response
@@ -741,11 +742,14 @@ lpfc_cmpl_ct_cmd_gid_ft(struct lpfc_hba *phba, struct lpfc_iocbq *cmdiocb,
 				goto out;
 
 			/* CT command is being retried */
-			vport->gidft_inp--;
 			rc = lpfc_ns_cmd(vport, SLI_CTNS_GID_FT,
 					 vport->fc_ns_retry, type);
 			if (rc == 0)
 				goto out;
+			else { /* Unable to send NS cmd */
+				if (vport->gidft_inp)
+					vport->gidft_inp--;
+			}
 		}
 		if (vport->fc_flag & FC_RSCN_MODE)
 			lpfc_els_flush_rscn(vport);
@@ -825,7 +829,8 @@ lpfc_cmpl_ct_cmd_gid_ft(struct lpfc_hba *phba, struct lpfc_iocbq *cmdiocb,
 				(uint32_t) CTrsp->ReasonCode,
 				(uint32_t) CTrsp->Explanation);
 		}
-		vport->gidft_inp--;
+		if (vport->gidft_inp)
+			vport->gidft_inp--;
 	}
 
 	lpfc_printf_vlog(vport, KERN_INFO, LOG_DISCOVERY,
@@ -918,7 +923,8 @@ lpfc_cmpl_ct_cmd_gid_pt(struct lpfc_hba *phba, struct lpfc_iocbq *cmdiocb,
 		/* This is a GID_PT completing so the gidft_inp counter was
 		 * incremented before the GID_PT was issued to the wire.
 		 */
-		vport->gidft_inp--;
+		if (vport->gidft_inp)
+			vport->gidft_inp--;
 
 		/*
 		 * Skip processing the NS response
@@ -942,11 +948,14 @@ lpfc_cmpl_ct_cmd_gid_pt(struct lpfc_hba *phba, struct lpfc_iocbq *cmdiocb,
 				vport->fc_ns_retry++;
 
 			/* CT command is being retried */
-			vport->gidft_inp--;
 			rc = lpfc_ns_cmd(vport, SLI_CTNS_GID_PT,
 					 vport->fc_ns_retry, GID_PT_N_PORT);
 			if (rc == 0)
 				goto out;
+			else { /* Unable to send NS cmd */
+				if (vport->gidft_inp)
+					vport->gidft_inp--;
+			}
 		}
 		if (vport->fc_flag & FC_RSCN_MODE)
 			lpfc_els_flush_rscn(vport);
@@ -1027,7 +1036,8 @@ lpfc_cmpl_ct_cmd_gid_pt(struct lpfc_hba *phba, struct lpfc_iocbq *cmdiocb,
 				(uint32_t)CTrsp->ReasonCode,
 				(uint32_t)CTrsp->Explanation);
 		}
-		vport->gidft_inp--;
+		if (vport->gidft_inp)
+			vport->gidft_inp--;
 	}
 
 	lpfc_printf_vlog(vport, KERN_INFO, LOG_DISCOVERY,