[PATCH 3.16 158/306] scsi: megaraid_sas: Fix data integrity failure for JBOD (passthrough) devices

[Ben Hutchings]

3.16.40-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Kashyap Desai <kashyap.desai@xxxxxxxxxxxx>

commit 1e793f6fc0db920400574211c48f9157a37e3945 upstream.

Commit 02b01e010afe ("megaraid_sas: return sync cache call with
success") modified the driver to successfully complete SYNCHRONIZE_CACHE
commands without passing them to the controller. Disk drive caches are
only explicitly managed by controller firmware when operating in RAID
mode. So this commit effectively disabled writeback cache flushing for
any drives used in JBOD mode, leading to data integrity failures.

[mkp: clarified patch description]

Fixes: 02b01e010afeeb49328d35650d70721d2ca3fd59
Signed-off-by: Kashyap Desai <kashyap.desai@xxxxxxxxxxxx>
Signed-off-by: Sumit Saxena <sumit.saxena@xxxxxxxxxxxx>
Reviewed-by: Tomas Henzl <thenzl@xxxxxxxxxx>
Reviewed-by: Hannes Reinecke <hare@xxxxxxxx>
Reviewed-by: Ewan D. Milne <emilne@xxxxxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/scsi/megaraid/megaraid_sas_base.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

--- a/drivers/scsi/megaraid/megaraid_sas_base.c
+++ b/drivers/scsi/megaraid/megaraid_sas_base.c
@@ -1586,16 +1586,13 @@ megasas_queue_command_lck(struct scsi_cm
 		goto out_done;
 	}
 
-	switch (scmd->cmnd[0]) {
-	case SYNCHRONIZE_CACHE:
-		/*
-		 * FW takes care of flush cache on its own
-		 * No need to send it down
-		 */
+	/*
+	 * FW takes care of flush cache on its own for Virtual Disk.
+	 * No need to send it down for VD. For JBOD send SYNCHRONIZE_CACHE to FW.
+	 */
+	if ((scmd->cmnd[0] == SYNCHRONIZE_CACHE) && MEGASAS_IS_LOGICAL(scmd)) {
 		scmd->result = DID_OK << 16;
 		goto out_done;
-	default:
-		break;
 	}
 
 	if (instance->instancet->build_and_issue_cmd(instance, scmd)) {