[PATCH AUTOSEL 3.18 20/22] scsi: lpfc: Correct soft lockup when running mds diagnostics

[Sasha Levin <sashal@kernel.org>]

From: James Smart <jsmart2021@gmail.com>

[ Upstream commit 0ef01a2d95fd62bb4f536e7ce4d5e8e74b97a244 ]

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>
---
 drivers/scsi/lpfc/lpfc_sli.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/scsi/lpfc/lpfc_sli.c b/drivers/scsi/lpfc/lpfc_sli.c
index cdade5828a5d..fcae6f66a5a6 100644
--- a/drivers/scsi/lpfc/lpfc_sli.c
+++ b/drivers/scsi/lpfc/lpfc_sli.c
@@ -3441,6 +3441,7 @@ 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;
@@ -3462,16 +3463,22 @@ 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;
 	}
 }
 
-- 
2.17.1