drbd: use the cached meta_dev_idx

Now we have the cached meta_dev_idx member,
we can get rid of a few rcu_read_lock() sections and rcu_dereference().

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index 104b7ce..5621df8 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -722,14 +722,10 @@
 {
 	sector_t md_size_sect = 0;
 	unsigned int al_size_sect = MD_32kB_SECT;
-	int meta_dev_idx;
-
-	rcu_read_lock();
-	meta_dev_idx = rcu_dereference(bdev->disk_conf)->meta_dev_idx;
 
 	bdev->md.md_offset = drbd_md_ss(bdev);
 
-	switch (meta_dev_idx) {
+	switch (bdev->md.meta_dev_idx) {
 	default:
 		/* v07 style fixed size indexed meta data */
 		bdev->md.md_size_sect = MD_128MB_SECT;
@@ -761,7 +757,6 @@
 		bdev->md.bm_offset   = -md_size_sect + MD_4kB_SECT;
 		break;
 	}
-	rcu_read_unlock();
 }
 
 /* input size is expected to be in KB */