drbd: fix resync throttling initialization

If for some reason DRBD resync was the only activity on a backend
device, drbd_rs_c_min_rate_throttle() would mistakenly decide that it is
still initialization time, and keep throttling the resync.

This patch explicitly initializes ->rs_last_events to the current
backend event counters, and drops the rs_last_events == 0 from the
throttle condition.

Reported-by: Mikhail Sugakov <[e-mail]>

Signed-off-by: Philipp Reisner <[e-mail]>
Signed-off-by: Lars Ellenberg <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/block/drbd/drbd_receiver.c

···
 			atomic_read(&device->rs_sect_ev);
 
 	if (atomic_read(&device->ap_actlog_cnt)
-	    || !device->rs_last_events || curr_events - device->rs_last_events > 64) {
+	    || curr_events - device->rs_last_events > 64) {
 		unsigned long rs_left;
 		int i;
 

drivers/block/drbd/drbd_state.c

···
 
 		set_ov_position(device, ns.conn);
 		device->rs_start = now;
-		device->rs_last_events = 0;
 		device->rs_last_sect_ev = 0;
 		device->ov_last_oos_size = 0;
 		device->ov_last_oos_start = 0;

drivers/block/drbd/drbd_worker.c

···
 
 void drbd_rs_controller_reset(struct drbd_device *device)
 {
+	struct gendisk *disk = device->ldev->backing_bdev->bd_contains->bd_disk;
 	struct fifo_buffer *plan;
 
 	atomic_set(&device->rs_sect_in, 0);
 	atomic_set(&device->rs_sect_ev, 0);
 	device->rs_in_flight = 0;
+	device->rs_last_events =
+		(int)part_stat_read(&disk->part0, sectors[0]) +
+		(int)part_stat_read(&disk->part0, sectors[1]);
 
 	/* Updating the RCU protected object in place is necessary since
 	   this function gets called from atomic context.
···
 		device->rs_failed    = 0;
 		device->rs_paused    = 0;
 		device->rs_same_csum = 0;
-		device->rs_last_events = 0;
 		device->rs_last_sect_ev = 0;
 		device->rs_total     = tw;
 		device->rs_start     = now;