Staging: zram: Fix memory leak by refcount mismatch

commit 1b672224 upstream.

As suggested by Minchan Kim and Jerome Marchand "The code in reset_store
get the block device (bdget_disk()) but it does not put it (bdput()) when
it's done using it. The usage count is therefore incremented but never
decremented."

This patch also puts bdput() for all error cases.
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/staging/zram/zram_sysfs.c

@@ -99,18 +99,23 @@ static ssize_t reset_store(struct device *dev,
 		return -ENOMEM;
 
 	/* Do not reset an active device! */
-	if (bdev->bd_holders)
-		return -EBUSY;
+	if (bdev->bd_holders) {
+		ret = -EBUSY;
+		goto out;
+	}
 
 	ret = strict_strtoul(buf, 10, &do_reset);
 	if (ret)
-		return ret;
+		goto out;
 
-	if (!do_reset)
-		return -EINVAL;
+	if (!do_reset) {
+		ret = -EINVAL;
+		goto out;
+	}
 
 	/* Make sure all pending I/O is finished */
 	fsync_bdev(bdev);
+	bdput(bdev);
 
 	down_write(&zram->init_lock);
 	if (zram->init_done)
@@ -118,6 +123,10 @@ static ssize_t reset_store(struct device *dev,
 	up_write(&zram->init_lock);
 
 	return len;
+
+out:
+	bdput(bdev);
+	return ret;
 }
 
 static ssize_t num_reads_show(struct device *dev,