[SCSI] mpt2sas: Fix for Driver oops, when loading driver with max_queue_depth...

[SCSI] mpt2sas: Fix for Driver oops, when loading driver with max_queue_depth command line option to a very small value

If the specified max_queue_depth setting is less than the
expected number of internal commands, then driver will calculate
the queue depth size to a negitive number. This negitive number
is actually a very large number because variable is unsigned
16bit integer. So, the driver will ask for a very large amount of
memory for message frames and resulting into oops as memory
allocation routines will not able to handle such a large request.

So, in order to limit this kind of oops, The driver need to set
the max_queue_depth to a scsi mid layer's can_queue value. Then
the overall message frames required for IO is minimum of either
(max_queue_depth plus internal commands) or the IOC global
credits.
Signed-off-by: Sreekanth Reddy <sreekanth.reddy@lsi.com>
Cc: <stable@kernel.org>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/mpt2sas/mpt2sas_base.c

@@ -2424,10 +2424,13 @@ _base_allocate_memory_pools(struct MPT2SAS_ADAPTER *ioc,  int sleep_flag)
 	}
 
 	/* command line tunables  for max controller queue depth */
-	if (max_queue_depth != -1)
-		max_request_credit = (max_queue_depth < facts->RequestCredit)
-		    ? max_queue_depth : facts->RequestCredit;
-	else
+	if (max_queue_depth != -1 && max_queue_depth != 0) {
+		max_request_credit = min_t(u16, max_queue_depth +
+			ioc->hi_priority_depth + ioc->internal_depth,
+			facts->RequestCredit);
+		if (max_request_credit > MAX_HBA_QUEUE_DEPTH)
+			max_request_credit =  MAX_HBA_QUEUE_DEPTH;
+	} else
 		max_request_credit = min_t(u16, facts->RequestCredit,
 		    MAX_HBA_QUEUE_DEPTH);
 
@@ -2502,7 +2505,7 @@ _base_allocate_memory_pools(struct MPT2SAS_ADAPTER *ioc,  int sleep_flag)
 	/* set the scsi host can_queue depth
 	 * with some internal commands that could be outstanding
 	 */
-	ioc->shost->can_queue = ioc->scsiio_depth - (2);
+	ioc->shost->can_queue = ioc->scsiio_depth;
 	dinitprintk(ioc, printk(MPT2SAS_INFO_FMT "scsi host: "
 	    "can_queue depth (%d)\n", ioc->name, ioc->shost->can_queue));