[RFC][PATCH]SCSI signal(I/O) failure causes no response

[Masao Fukuchi <fukuchi.masao@jp.fujitsu.com>]

Hi all,

We are planning to use linux for enterprise server.
Since the response time on hardware failure is important factor,
we are measuring the response time in case of the error by making
pseudo errors.

We generated some SCSI signal failure in the test.
When I cut the I/O signal during read command from host, 
I expected the command finished with error soon.
But the result was the command didn't finish forever(and no error
message was displayed).

I added some messages in order to investigate what has occurred.
>From the messages, the sequence was:

1.Fusion MPT driver issues read command to its firmware.
  (our server has LSI53C1030 as SCSI adapter)
  Then the firmware returns protocol error for the command.
  Fusion MPT driver makes DID_RESET status by protocol error 
  and sends it to SCSI midlayer.

2.SCSI midlayer analyzes the status from LLD.
  SCSI midlayer schedules command retry because the status is just
  DID_RESET status.
  (When the status has DID_RESET plus some sense code, the retry
   sequence depends on the sense code. But when the status has only
   DID_RESET, SCSI midlayer schedules command retry)

Sequence 1. and 2. are repeated infinitely and it causes no response.

To prevent this problem, I proposed Eric Moore to change the DID_RESET
status to DID_SOFT_ERROR in fusion MPT driver.
But he suggested me to change SCSI midlayer to prevent infinite loop.

So, I made following patch to prevent the problem.
(patch is based on kernel 2.6.5)

Comments welcome.

Thanks,
Masao Fukuchi

///
diff -uarN linux-2.6.5/drivers/scsi/scsi_lib.c linux-didreset/drivers/scsi/scsi_lib.c
--- linux-2.6.5/drivers/scsi/scsi_lib.c	2004-04-13 18:53:52.000000000 +0900
+++ linux-didreset/drivers/scsi/scsi_lib.c	2004-04-13 20:32:23.000000000 +0900
@@ -852,8 +852,10 @@
 		 * recovery reasons.  Just retry the request
 		 * and see what happens.  
 		 */
-		scsi_requeue_command(q, cmd);
-		return;
+		if (++cmd->retries < cmd->allowed) {
+			scsi_requeue_command(q, cmd);
+			return;
+		}
 	}
 	if (result) {
 		printk("SCSI error : <%d %d %d %d> return code = 0x%x\n",