This patch fixes q->unplug_thresh condition check in

__elv_add_request().  rq.count[READ] + rq.count[WRITE] can increase
more than one if another thread has allocated a request after the
current request is allocated or in_flight could have changed resulting
in larger-than-one change of nrq, thus breaking the threshold
mechanism.
Signed-off-by: NJens Axboe <axboe@suse.de>
Signed-off-by: NTejun Heo <htejun@gmail.com>

drivers/block/elevator.c

@@ -317,7 +317,7 @@ void __elv_add_request(request_queue_t *q, struct request *rq, int where,
 			int nrq = q->rq.count[READ] + q->rq.count[WRITE]
 				  - q->in_flight;
 
-			if (nrq == q->unplug_thresh)
+			if (nrq >= q->unplug_thresh)
 				__generic_unplug_device(q);
 		}
 	} else