blk-throttle: remove blk_throtl_drain

After the commit 5addeae1 ("blk-cgroup: remove blkcg_drain_queue"),
there is no caller of blk_throtl_drain, so let's remove it.
Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-throttle.c

@@ -2380,47 +2380,6 @@ static void tg_drain_bios(struct throtl_service_queue *parent_sq)
 	}
 }
 
-/**
- * blk_throtl_drain - drain throttled bios
- * @q: request_queue to drain throttled bios for
- *
- * Dispatch all currently throttled bios on @q through ->make_request_fn().
- */
-void blk_throtl_drain(struct request_queue *q)
-	__releases(&q->queue_lock) __acquires(&q->queue_lock)
-{
-	struct throtl_data *td = q->td;
-	struct blkcg_gq *blkg;
-	struct cgroup_subsys_state *pos_css;
-	struct bio *bio;
-	int rw;
-
-	rcu_read_lock();
-
-	/*
-	 * Drain each tg while doing post-order walk on the blkg tree, so
-	 * that all bios are propagated to td->service_queue.  It'd be
-	 * better to walk service_queue tree directly but blkg walk is
-	 * easier.
-	 */
-	blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg)
-		tg_drain_bios(&blkg_to_tg(blkg)->service_queue);
-
-	/* finally, transfer bios from top-level tg's into the td */
-	tg_drain_bios(&td->service_queue);
-
-	rcu_read_unlock();
-	spin_unlock_irq(&q->queue_lock);
-
-	/* all bios now should be in td->service_queue, issue them */
-	for (rw = READ; rw <= WRITE; rw++)
-		while ((bio = throtl_pop_queued(&td->service_queue.queued[rw],
-						NULL)))
-			generic_make_request(bio);
-
-	spin_lock_irq(&q->queue_lock);
-}
-
 int blk_throtl_init(struct request_queue *q)
 {
 	struct throtl_data *td;

block/blk.h

@@ -296,12 +296,10 @@ int create_task_io_context(struct task_struct *task, gfp_t gfp_mask, int node);
  * Internal throttling interface
  */
 #ifdef CONFIG_BLK_DEV_THROTTLING
-extern void blk_throtl_drain(struct request_queue *q);
 extern int blk_throtl_init(struct request_queue *q);
 extern void blk_throtl_exit(struct request_queue *q);
 extern void blk_throtl_register_queue(struct request_queue *q);
 #else /* CONFIG_BLK_DEV_THROTTLING */
-static inline void blk_throtl_drain(struct request_queue *q) { }
 static inline int blk_throtl_init(struct request_queue *q) { return 0; }
 static inline void blk_throtl_exit(struct request_queue *q) { }
 static inline void blk_throtl_register_queue(struct request_queue *q) { }