btrfs: volumes: remove unnecessary calls to btrfs_mark_buffer_dirty()

We have several places explicitly calling btrfs_mark_buffer_dirty() but
that is not necessarily since the target leaf came from a path that was
obtained for a btree search function that modifies the btree, something
like btrfs_insert_empty_item() or anything else that ends up calling
btrfs_search_slot() with a value of 1 for its 'cow' argument.

These just make the code more verbose, confusing and add a little extra
overhead and well as increase the module's text size, so remove them.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -2069,7 +2069,6 @@ static int btrfs_add_dev_item(struct btrfs_trans_handle *trans,
 	ptr = btrfs_device_fsid(dev_item);
 	write_extent_buffer(leaf, trans->fs_info->fs_devices->metadata_uuid,
 			    ptr, BTRFS_FSID_SIZE);
-	btrfs_mark_buffer_dirty(trans, leaf);
 
 	ret = 0;
 out:
@@ -2765,11 +2764,9 @@ static int btrfs_finish_sprout(struct btrfs_trans_handle *trans)
 		device = btrfs_find_device(fs_info->fs_devices, &args);
 		BUG_ON(!device); /* Logic error */
 
-		if (device->fs_devices->seeding) {
+		if (device->fs_devices->seeding)
 			btrfs_set_device_generation(leaf, dev_item,
 						    device->generation);
-			btrfs_mark_buffer_dirty(trans, leaf);
-		}
 
 		path->slots[0]++;
 		goto next_slot;
@@ -3062,8 +3059,6 @@ static noinline int btrfs_update_device(struct btrfs_trans_handle *trans,
 				     btrfs_device_get_disk_total_bytes(device));
 	btrfs_set_device_bytes_used(leaf, dev_item,
 				    btrfs_device_get_bytes_used(device));
-	btrfs_mark_buffer_dirty(trans, leaf);
-
 out:
 	btrfs_free_path(path);
 	return ret;
@@ -3772,10 +3767,7 @@ static int insert_balance_item(struct btrfs_fs_info *fs_info,
 	btrfs_set_balance_meta(leaf, item, &disk_bargs);
 	btrfs_cpu_balance_args_to_disk(&disk_bargs, &bctl->sys);
 	btrfs_set_balance_sys(leaf, item, &disk_bargs);
-
 	btrfs_set_balance_flags(leaf, item, bctl->flags);
-
-	btrfs_mark_buffer_dirty(trans, leaf);
 out:
 	btrfs_free_path(path);
 	err = btrfs_commit_transaction(trans);
@@ -7799,8 +7791,6 @@ static int update_dev_stat_item(struct btrfs_trans_handle *trans,
 	for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++)
 		btrfs_set_dev_stats_value(eb, ptr, i,
 					  btrfs_dev_stat_read(device, i));
-	btrfs_mark_buffer_dirty(trans, eb);
-
 out:
 	btrfs_free_path(path);
 	return ret;