mtd: mtd_blkdevs: fix error path in blktrans_open

The 'blktrans_open()' does not handle possible '__get_mtd_device()' failures
because it does not check the error code. Moreover, the 'dev->tr->open()'
failures are not handled correctly because in this case the function just
goes ahead and gets the mtd device, then returns an error. But Instead, it
should _not_ try to get the mtd device, then it should put back the module
and the kref.

This patch fixes the issue. Note, I only compile-tested it. This patch was
inspired by a bug report about a similar issue in 2.6.34 kernels
sent by Mike Turner <admin@islandsoftware.co.uk> to the MTD mailing list:

http://lists.infradead.org/pipermail/linux-mtd/2011-April/034980.html

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/mtd_blkdevs.c

@@ -221,15 +221,33 @@ static int blktrans_open(struct block_device *bdev, fmode_t mode)
 	kref_get(&dev->ref);
 	__module_get(dev->tr->owner);
 
-	if (dev->mtd) {
-		ret = dev->tr->open ? dev->tr->open(dev) : 0;
-		__get_mtd_device(dev->mtd);
+	if (!dev->mtd)
+		goto unlock;
+
+	if (dev->tr->open) {
+		ret = dev->tr->open(dev);
+		if (ret)
+			goto error_put;
 	}
 
+	ret = __get_mtd_device(dev->mtd);
+	if (ret)
+		goto error_release;
+
 unlock:
 	mutex_unlock(&dev->lock);
 	blktrans_dev_put(dev);
 	return ret;
+
+error_release:
+	if (dev->tr->release)
+		dev->tr->release(dev);
+error_put:
+	module_put(dev->tr->owner);
+	kref_put(&dev->ref, blktrans_dev_release);
+	mutex_unlock(&dev->lock);
+	blktrans_dev_put(dev);
+	return ret;
 }
 
 static int blktrans_release(struct gendisk *disk, fmode_t mode)