s390/dasd: simplify locking in dasd_times_out

Provide __dasd_cancel_req that is called with the ccw device lock
held to simplify the locking in dasd_times_out. Also this removes
the following sparse warning:
context imbalance in 'dasd_times_out' - different lock contexts for basic block

Note: with this change dasd_schedule_device_bh is now called (via
dasd_cancel_req) with the ccw device lock held. But is is already
the case for other codepaths.
Signed-off-by: Sebastian Ott <sebott@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/block/dasd.c

@@ -2569,14 +2569,11 @@ EXPORT_SYMBOL(dasd_sleep_on_immediatly);
  * Cancellation of a request is an asynchronous operation! The calling
  * function has to wait until the request is properly returned via callback.
  */
-int dasd_cancel_req(struct dasd_ccw_req *cqr)
+static int __dasd_cancel_req(struct dasd_ccw_req *cqr)
 {
 	struct dasd_device *device = cqr->startdev;
-	unsigned long flags;
-	int rc;
+	int rc = 0;
 
-	rc = 0;
-	spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 	switch (cqr->status) {
 	case DASD_CQR_QUEUED:
 		/* request was not started - just set to cleared */
@@ -2596,11 +2593,21 @@ int dasd_cancel_req(struct dasd_ccw_req *cqr)
 	default: /* already finished or clear pending - do nothing */
 		break;
 	}
-	spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 	dasd_schedule_device_bh(device);
 	return rc;
 }
-EXPORT_SYMBOL(dasd_cancel_req);
+
+int dasd_cancel_req(struct dasd_ccw_req *cqr)
+{
+	struct dasd_device *device = cqr->startdev;
+	unsigned long flags;
+	int rc;
+
+	spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
+	rc = __dasd_cancel_req(cqr);
+	spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
+	return rc;
+}
 
 /*
  * SECTION: Operations of the dasd_block layer.
@@ -3082,12 +3089,10 @@ enum blk_eh_timer_return dasd_times_out(struct request *req, bool reserved)
 	cqr->retries = -1;
 	cqr->intrc = -ETIMEDOUT;
 	if (cqr->status >= DASD_CQR_QUEUED) {
-		spin_unlock(get_ccwdev_lock(device->cdev));
-		rc = dasd_cancel_req(cqr);
+		rc = __dasd_cancel_req(cqr);
 	} else if (cqr->status == DASD_CQR_FILLED ||
 		   cqr->status == DASD_CQR_NEED_ERP) {
 		cqr->status = DASD_CQR_TERMINATED;
-		spin_unlock(get_ccwdev_lock(device->cdev));
 	} else if (cqr->status == DASD_CQR_IN_ERP) {
 		struct dasd_ccw_req *searchcqr, *nextcqr, *tmpcqr;
 
@@ -3102,9 +3107,7 @@ enum blk_eh_timer_return dasd_times_out(struct request *req, bool reserved)
 			searchcqr->retries = -1;
 			searchcqr->intrc = -ETIMEDOUT;
 			if (searchcqr->status >= DASD_CQR_QUEUED) {
-				spin_unlock(get_ccwdev_lock(device->cdev));
-				rc = dasd_cancel_req(searchcqr);
-				spin_lock(get_ccwdev_lock(device->cdev));
+				rc = __dasd_cancel_req(searchcqr);
 			} else if ((searchcqr->status == DASD_CQR_FILLED) ||
 				   (searchcqr->status == DASD_CQR_NEED_ERP)) {
 				searchcqr->status = DASD_CQR_TERMINATED;
@@ -3118,8 +3121,8 @@ enum blk_eh_timer_return dasd_times_out(struct request *req, bool reserved)
 			}
 			break;
 		}
-		spin_unlock(get_ccwdev_lock(device->cdev));
 	}
+	spin_unlock(get_ccwdev_lock(device->cdev));
 	dasd_schedule_block_bh(block);
 	spin_unlock(&block->queue_lock);
 	spin_unlock_irqrestore(&cqr->dq->lock, flags);