[SCSI] Derive the FLUSH_TIMEOUT from the basic I/O timeout

Rather than having a separate constant for specifying the timeout on FLUSH
operations, use the basic I/O timeout value that is already configurable
on a per target basis to derive the FLUSH timeout. Looking at the current
definitions of these timeout values, the FLUSH operation is supposed to have
a value that is twice the normal timeout value. This patch preserves this
relationship while leveraging the flexibility of specifying the I/O timeout.

Based on a prior patch by KY Srinivasan <kys@microsoft.com>
Reviewed-by: KY Srinivasan <kys@microsoft.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/sd.c

@@ -830,7 +830,7 @@ static int sd_setup_write_same_cmnd(struct scsi_device *sdp, struct request *rq)
 
 static int scsi_setup_flush_cmnd(struct scsi_device *sdp, struct request *rq)
 {
-	rq->timeout = SD_FLUSH_TIMEOUT;
+	rq->timeout *= SD_FLUSH_TIMEOUT_MULTIPLIER;
 	rq->retries = SD_MAX_RETRIES;
 	rq->cmd[0] = SYNCHRONIZE_CACHE;
 	rq->cmd_len = 10;
@@ -1434,6 +1434,8 @@ static int sd_sync_cache(struct scsi_disk *sdkp)
 {
 	int retries, res;
 	struct scsi_device *sdp = sdkp->device;
+	const int timeout = sdp->request_queue->rq_timeout
+		* SD_FLUSH_TIMEOUT_MULTIPLIER;
 	struct scsi_sense_hdr sshdr;
 
 	if (!scsi_device_online(sdp))
@@ -1448,8 +1450,8 @@ static int sd_sync_cache(struct scsi_disk *sdkp)
 		 * flush everything.
 		 */
 		res = scsi_execute_req_flags(sdp, cmd, DMA_NONE, NULL, 0,
-					     &sshdr, SD_FLUSH_TIMEOUT,
-					     SD_MAX_RETRIES, NULL, REQ_PM);
+					     &sshdr, timeout, SD_MAX_RETRIES,
+					     NULL, REQ_PM);
 		if (res == 0)
 			break;
 	}

drivers/scsi/sd.h

@@ -13,7 +13,11 @@
  */
 #define SD_TIMEOUT		(30 * HZ)
 #define SD_MOD_TIMEOUT		(75 * HZ)
-#define SD_FLUSH_TIMEOUT	(60 * HZ)
+/*
+ * Flush timeout is a multiplier over the standard device timeout which is
+ * user modifiable via sysfs but initially set to SD_TIMEOUT
+ */
+#define SD_FLUSH_TIMEOUT_MULTIPLIER	2
 #define SD_WRITE_SAME_TIMEOUT	(120 * HZ)
 
 /*