scsi disk: disk offline prematurely from medium access timeout

There is an error with the medium access timeout feature of the sd driver. The sdkp->medium_access_timed_out value is set to zero in sd_done() in the wrong place. It is set to zero only if a command returns sense data. If an I/O command times out, error handling succeeds, and the I/O command completes, the value won't be reset if nothing generates a sense response. Then, another timeout (no matter how far in the future) can increment it again, causing the device to be prematurely set offline.

The resetting of sdkp->medium_access_timed_out should occur before the check for sense data.

---

To reproduce using scsi_debug, use SCSI_DEBUG_OPT_TIMEOUT or SCSI_DEBUG_OPT_MAC_TIMEOUT to force an I/O command to timeout. Then, remove the opt value so the I/O will succeed on retry. Perform more I/O as desired. Finally, repeat the process to make a new I/O command time out. Without the patch, the device will be marked offline even though many I/O commands have succeeded between the 2 instances of timed out commands.

index 86fcf2c..2779e6b 100644
@@ -1669,12 +1669,12 @@ static int sd_done(struct scsi_cmnd *SCpnt)
 						   sshdr.ascq));
 	}
 #endif
+	sdkp->medium_access_timed_out = 0;
+
 	if (driver_byte(result) != DRIVER_SENSE &&
 	    (!sense_valid || sense_deferred))
 		goto out;
 
-	sdkp->medium_access_timed_out = 0;
-
 	switch (sshdr.sense_key) {
 	case HARDWARE_ERROR:
 	case MEDIUM_ERROR: