1. Remove congested_fn and drbd_congested due to
    21cf866145047f8bfecb38ec8d2fed64464c074f
2. Change define of blkdev_get_by_path from fs.h to blkdev.h,
    3f1266f1f82d7b8c72472a8921e80aa3e611fb62
3. Change define of bd_unlink_disk_holder from fs.h to genhd.h,
    3f1266f1f82d7b8c72472a8921e80aa3e611fb62

diff -Naur drbd-9.0.25~0+git.bd41626d.orig/drbd/drbd-kernel-compat/drbd_wrappers.h drbd-9.0.25~0+git.bd41626d/drbd/drbd-kernel-compat/drbd_wrappers.h
--- drbd-9.0.25~0+git.bd41626d.orig/drbd/drbd-kernel-compat/drbd_wrappers.h	2020-10-10 10:50:15.408562371 +0800
+++ drbd-9.0.25~0+git.bd41626d/drbd/drbd-kernel-compat/drbd_wrappers.h	2020-10-10 10:50:21.156601464 +0800
@@ -143,9 +143,7 @@
 
 #ifdef COMPAT_HAVE_POINTER_BACKING_DEV_INFO /* >= v4.11 */
 #define bdi_from_device(device) (device->ldev->backing_bdev->bd_disk->queue->backing_dev_info)
-#define init_bdev_info(bdev_info, drbd_congested, device) do { \
-	(bdev_info)->congested_fn = drbd_congested; \
-	(bdev_info)->congested_data = device; \
+#define init_bdev_info(bdev_info, device) do { \
 	set_bdi_cap_stable_writes(bdev_info->capabilities); \
 } while(0)
 #define adjust_ra_pages(q, b) _adjust_ra_pages((q)->backing_dev_info->ra_pages, (b)->backing_dev_info->ra_pages)
diff -Naur drbd-9.0.25~0+git.bd41626d.orig/drbd/drbd-kernel-compat/tests/have_bd_unlink_disk_holder.c drbd-9.0.25~0+git.bd41626d/drbd/drbd-kernel-compat/tests/have_bd_unlink_disk_holder.c
--- drbd-9.0.25~0+git.bd41626d.orig/drbd/drbd-kernel-compat/tests/have_bd_unlink_disk_holder.c	2020-10-10 10:50:15.408562371 +0800
+++ drbd-9.0.25~0+git.bd41626d/drbd/drbd-kernel-compat/tests/have_bd_unlink_disk_holder.c	2020-10-10 10:50:29.488658135 +0800
@@ -1,4 +1,5 @@
 #include <linux/fs.h>
+#include <linux/genhd.h>
 
 #ifdef CONFIG_SYSFS
 void dummy(struct block_device *bdev, struct gendisk *disk)
diff -Naur drbd-9.0.25~0+git.bd41626d.orig/drbd/drbd-kernel-compat/tests/have_blkdev_get_by_path.c drbd-9.0.25~0+git.bd41626d/drbd/drbd-kernel-compat/tests/have_blkdev_get_by_path.c
--- drbd-9.0.25~0+git.bd41626d.orig/drbd/drbd-kernel-compat/tests/have_blkdev_get_by_path.c	2020-10-10 10:50:15.408562371 +0800
+++ drbd-9.0.25~0+git.bd41626d/drbd/drbd-kernel-compat/tests/have_blkdev_get_by_path.c	2020-10-10 10:50:40.432732559 +0800
@@ -1,4 +1,5 @@
 #include <linux/fs.h>
+#include <linux/blkdev.h>
 
 /*
  * In kernel version 2.6.38-rc1, open_bdev_exclusive() was replaced by
diff -Naur drbd-9.0.25~0+git.bd41626d.orig/drbd/drbd_main.c drbd-9.0.25~0+git.bd41626d/drbd/drbd_main.c
--- drbd-9.0.25~0+git.bd41626d.orig/drbd/drbd_main.c	2020-10-10 10:50:15.412562399 +0800
+++ drbd-9.0.25~0+git.bd41626d/drbd/drbd_main.c	2020-10-10 10:50:21.156601464 +0800
@@ -3103,63 +3103,6 @@
 	pr_info("module cleanup done.\n");
 }
 
-/**
- * drbd_congested() - Callback for the flusher thread
- * @congested_data:	User data
- * @bdi_bits:		Bits the BDI flusher thread is currently interested in
- *
- * Returns 1<<WB_async_congested and/or 1<<WB_sync_congested if we are congested.
- */
-static int drbd_congested(void *congested_data, int bdi_bits)
-{
-	struct drbd_device *device = congested_data;
-	struct request_queue *q;
-	int r = 0;
-
-	if (!may_inc_ap_bio(device)) {
-		/* DRBD has frozen IO */
-		r = bdi_bits;
-		goto out;
-	}
-
-	if (test_bit(CALLBACK_PENDING, &device->resource->flags)) {
-		r |= (1 << WB_async_congested);
-		/* Without good local data, we would need to read from remote,
-		 * and that would need the worker thread as well, which is
-		 * currently blocked waiting for that usermode helper to
-		 * finish.
-		 */
-		if (!get_ldev_if_state(device, D_UP_TO_DATE))
-			r |= (1 << WB_sync_congested);
-		else
-			put_ldev(device);
-		r &= bdi_bits;
-		goto out;
-	}
-
-	if (get_ldev(device)) {
-		q = bdev_get_queue(device->ldev->backing_bdev);
-		r = bdi_congested(q->backing_dev_info, bdi_bits);
-		put_ldev(device);
-	}
-
-	if (bdi_bits & (1 << WB_async_congested)) {
-		struct drbd_peer_device *peer_device;
-
-		rcu_read_lock();
-		for_each_peer_device_rcu(peer_device, device) {
-			if (test_bit(NET_CONGESTED, &peer_device->connection->transport.flags)) {
-				r |= (1 << WB_async_congested);
-				break;
-			}
-		}
-		rcu_read_unlock();
-	}
-
-out:
-	return r;
-}
-
 static void drbd_init_workqueue(struct drbd_work_queue* wq)
 {
 	spin_lock_init(&wq->q_lock);
@@ -3731,7 +3674,7 @@
 	/* we have no partitions. we contain only ourselves. */
 	device->this_bdev->bd_contains = device->this_bdev;
 
-	init_bdev_info(q->backing_dev_info, drbd_congested, device);
+	init_bdev_info(q->backing_dev_info, device);
 
 	blk_queue_write_cache(q, true, true);