block, bdi: an active gendisk always has a request_queue associated with it

bdev_get_queue() returns the request_queue associated with the
specified block_device.  blk_get_backing_dev_info() makes use of
bdev_get_queue() to determine the associated bdi given a block_device.

All the callers of bdev_get_queue() including
blk_get_backing_dev_info() assume that bdev_get_queue() may return
NULL and implement NULL handling; however, bdev_get_queue() requires
the passed in block_device is opened and attached to its gendisk.
Because an active gendisk always has a valid request_queue associated
with it, bdev_get_queue() can never return NULL and neither can
blk_get_backing_dev_info().

Make it clear that neither of the two functions can return NULL and
remove NULL handling from all the callers.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Chris Mason <clm@fb.com>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index d0ed9e6..39ff591 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1694,7 +1694,7 @@
 		if (!device->bdev)
 			continue;
 		bdi = blk_get_backing_dev_info(device->bdev);
-		if (bdi && bdi_congested(bdi, bdi_bits)) {
+		if (bdi_congested(bdi, bdi_bits)) {
 			ret = 1;
 			break;
 		}