scsi: lpfc: Correct soft lockup when running mds diagnostics

BugLink: https://bugs.launchpad.net/bugs/1810947

[ Upstream commit 0ef01a2d ]

When running an mds diagnostic that passes frames with the switch, soft
lockups are detected. The driver is in a CQE processing loop and has
sufficient amount of traffic that it never exits the ring processing routine,
thus the "lockup".

Cap the number of elements in the work processing routine to 64 elements. This
ensures that the cpu will be given up and the handler reschedule to process
additional items.
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/scsi/lpfc/lpfc_sli.c

@@ -3485,6 +3485,7 @@ lpfc_sli_handle_slow_ring_event_s4(struct lpfc_hba *phba,
 	struct hbq_dmabuf *dmabuf;
 	struct lpfc_cq_event *cq_event;
 	unsigned long iflag;
+	int count = 0;
 
 	spin_lock_irqsave(&phba->hbalock, iflag);
 	phba->hba_flag &= ~HBA_SP_QUEUE_EVT;
@@ -3506,16 +3507,22 @@ lpfc_sli_handle_slow_ring_event_s4(struct lpfc_hba *phba,
 			if (irspiocbq)
 				lpfc_sli_sp_handle_rspiocb(phba, pring,
 							   irspiocbq);
+			count++;
 			break;
 		case CQE_CODE_RECEIVE:
 		case CQE_CODE_RECEIVE_V1:
 			dmabuf = container_of(cq_event, struct hbq_dmabuf,
 					      cq_event);
 			lpfc_sli4_handle_received_buffer(phba, dmabuf);
+			count++;
 			break;
 		default:
 			break;
 		}
+
+		/* Limit the number of events to 64 to avoid soft lockups */
+		if (count == 64)
+			break;
 	}
 }