1 files changed, 248 insertions, 317 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index c7836a1ded973..bf90684a007a2 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -39,6 +39,26 @@
 static DEFINE_MUTEX(all_q_mutex);
 static LIST_HEAD(all_q_list);
 
+static void blk_mq_poll_stats_start(struct request_queue *q);
+static void blk_mq_poll_stats_fn(struct blk_stat_callback *cb);
+
+static int blk_mq_poll_stats_bkt(const struct request *rq)
+{
+	int ddir, bytes, bucket;
+
+	ddir = rq_data_dir(rq);
+	bytes = blk_rq_bytes(rq);
+
+	bucket = ddir + 2*(ilog2(bytes) - 9);
+
+	if (bucket < 0)
+		return -1;
+	else if (bucket >= BLK_MQ_POLL_STATS_BKTS)
+		return ddir + BLK_MQ_POLL_STATS_BKTS - 2;
+
+	return bucket;
+}
+
 /*
  * Check if any of the ctx's have pending work in this hardware queue
  */
@@ -65,7 +85,7 @@ static void blk_mq_hctx_clear_pending(struct blk_mq_hw_ctx *hctx,
 	sbitmap_clear_bit(&hctx->ctx_map, ctx->index_hw);
 }
 
-void blk_mq_freeze_queue_start(struct request_queue *q)
+void blk_freeze_queue_start(struct request_queue *q)
 {
 	int freeze_depth;
 
@@ -75,7 +95,7 @@ void blk_mq_freeze_queue_start(struct request_queue *q)
 		blk_mq_run_hw_queues(q, false);
 	}
 }
-EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_start);
+EXPORT_SYMBOL_GPL(blk_freeze_queue_start);
 
 void blk_mq_freeze_queue_wait(struct request_queue *q)
 {
@@ -105,7 +125,7 @@ void blk_freeze_queue(struct request_queue *q)
 	 * no blk_unfreeze_queue(), and blk_freeze_queue() is not
 	 * exported to drivers as the only user for unfreeze is blk_mq.
 	 */
-	blk_mq_freeze_queue_start(q);
+	blk_freeze_queue_start(q);
 	blk_mq_freeze_queue_wait(q);
 }
 
@@ -210,7 +230,6 @@ void blk_mq_rq_ctx_init(struct request_queue *q, struct blk_mq_ctx *ctx,
 #endif
 	rq->special = NULL;
 	/* tag was already set */
-	rq->errors = 0;
 	rq->extra_len = 0;
 
 	INIT_LIST_HEAD(&rq->timeout_list);
@@ -347,7 +366,7 @@ void __blk_mq_finish_request(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
 	if (rq->tag != -1)
 		blk_mq_put_tag(hctx, hctx->tags, ctx, rq->tag);
 	if (sched_tag != -1)
-		blk_mq_sched_completed_request(hctx, rq);
+		blk_mq_put_tag(hctx, hctx->sched_tags, ctx, sched_tag);
 	blk_mq_sched_restart(hctx);
 	blk_queue_exit(q);
 }
@@ -365,6 +384,7 @@ void blk_mq_finish_request(struct request *rq)
 {
 	blk_mq_finish_hctx_request(blk_mq_map_queue(rq->q, rq->mq_ctx->cpu), rq);
 }
+EXPORT_SYMBOL_GPL(blk_mq_finish_request);
 
 void blk_mq_free_request(struct request *rq)
 {
@@ -402,12 +422,19 @@ static void __blk_mq_complete_request_remote(void *data)
 	rq->q->softirq_done_fn(rq);
 }
 
-static void blk_mq_ipi_complete_request(struct request *rq)
+static void __blk_mq_complete_request(struct request *rq)
 {
 	struct blk_mq_ctx *ctx = rq->mq_ctx;
 	bool shared = false;
 	int cpu;
 
+	if (rq->internal_tag != -1)
+		blk_mq_sched_completed_request(rq);
+	if (rq->rq_flags & RQF_STATS) {
+		blk_mq_poll_stats_start(rq->q);
+		blk_stat_add(rq);
+	}
+
 	if (!test_bit(QUEUE_FLAG_SAME_COMP, &rq->q->queue_flags)) {
 		rq->q->softirq_done_fn(rq);
 		return;
@@ -428,33 +455,6 @@ static void blk_mq_ipi_complete_request(struct request *rq)
 	put_cpu();
 }
 
-static void blk_mq_stat_add(struct request *rq)
-{
-	if (rq->rq_flags & RQF_STATS) {
-		/*
-		 * We could rq->mq_ctx here, but there's less of a risk
-		 * of races if we have the completion event add the stats
-		 * to the local software queue.
-		 */
-		struct blk_mq_ctx *ctx;
-
-		ctx = __blk_mq_get_ctx(rq->q, raw_smp_processor_id());
-		blk_stat_add(&ctx->stat[rq_data_dir(rq)], rq);
-	}
-}
-
-static void __blk_mq_complete_request(struct request *rq)
-{
-	struct request_queue *q = rq->q;
-
-	blk_mq_stat_add(rq);
-
-	if (!q->softirq_done_fn)
-		blk_mq_end_request(rq, rq->errors);
-	else
-		blk_mq_ipi_complete_request(rq);
-}
-
 /**
  * blk_mq_complete_request - end I/O on a request
  * @rq:		the request being processed
@@ -463,16 +463,14 @@ static void __blk_mq_complete_request(struct request *rq)
  *	Ends all I/O on a request. It does not handle partial completions.
  *	The actual completion happens out-of-order, through a IPI handler.
  **/
-void blk_mq_complete_request(struct request *rq, int error)
+void blk_mq_complete_request(struct request *rq)
 {
 	struct request_queue *q = rq->q;
 
 	if (unlikely(blk_should_fake_timeout(q)))
 		return;
-	if (!blk_mark_rq_complete(rq)) {
-		rq->errors = error;
+	if (!blk_mark_rq_complete(rq))
 		__blk_mq_complete_request(rq);
-	}
 }
 EXPORT_SYMBOL(blk_mq_complete_request);
 
@@ -491,7 +489,7 @@ void blk_mq_start_request(struct request *rq)
 	trace_block_rq_issue(q, rq);
 
 	if (test_bit(QUEUE_FLAG_STATS, &q->queue_flags)) {
-		blk_stat_set_issue_time(&rq->issue_stat);
+		blk_stat_set_issue(&rq->issue_stat, blk_rq_sectors(rq));
 		rq->rq_flags |= RQF_STATS;
 		wbt_issue(q->rq_wb, &rq->issue_stat);
 	}
@@ -526,6 +524,15 @@ void blk_mq_start_request(struct request *rq)
 }
 EXPORT_SYMBOL(blk_mq_start_request);
 
+/*
+ * When we reach here because queue is busy, REQ_ATOM_COMPLETE
+ * flag isn't set yet, so there may be race with timeout handler,
+ * but given rq->deadline is just set in .queue_rq() under
+ * this situation, the race won't be possible in reality because
+ * rq->timeout should be set as big enough to cover the window
+ * between blk_mq_start_request() called from .queue_rq() and
+ * clearing REQ_ATOM_STARTED here.
+ */
 static void __blk_mq_requeue_request(struct request *rq)
 {
 	struct request_queue *q = rq->q;
@@ -633,8 +640,7 @@ void blk_mq_abort_requeue_list(struct request_queue *q)
 
 		rq = list_first_entry(&rq_list, struct request, queuelist);
 		list_del_init(&rq->queuelist);
-		rq->errors = -EIO;
-		blk_mq_end_request(rq, rq->errors);
+		blk_mq_end_request(rq, -EIO);
 	}
 }
 EXPORT_SYMBOL(blk_mq_abort_requeue_list);
@@ -666,7 +672,7 @@ void blk_mq_rq_timed_out(struct request *req, bool reserved)
 	 * just be ignored. This can happen due to the bitflag ordering.
 	 * Timeout first checks if STARTED is set, and if it is, assumes
 	 * the request is active. But if we race with completion, then
-	 * we both flags will get cleared. So check here again, and ignore
+	 * both flags will get cleared. So check here again, and ignore
 	 * a timeout event with a request that isn't active.
 	 */
 	if (!test_bit(REQ_ATOM_STARTED, &req->atomic_flags))
@@ -699,6 +705,19 @@ static void blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
 	if (!test_bit(REQ_ATOM_STARTED, &rq->atomic_flags))
 		return;
 
+	/*
+	 * The rq being checked may have been freed and reallocated
+	 * out already here, we avoid this race by checking rq->deadline
+	 * and REQ_ATOM_COMPLETE flag together:
+	 *
+	 * - if rq->deadline is observed as new value because of
+	 *   reusing, the rq won't be timed out because of timing.
+	 * - if rq->deadline is observed as previous value,
+	 *   REQ_ATOM_COMPLETE flag won't be cleared in reuse path
+	 *   because we put a barrier between setting rq->deadline
+	 *   and clearing the flag in blk_mq_start_request(), so
+	 *   this rq won't be timed out too.
+	 */
 	if (time_after_eq(jiffies, rq->deadline)) {
 		if (!blk_mark_rq_complete(rq))
 			blk_mq_rq_timed_out(rq, reserved);
@@ -727,7 +746,7 @@ static void blk_mq_timeout_work(struct work_struct *work)
 	 * percpu_ref_tryget directly, because we need to be able to
 	 * obtain a reference even in the short window between the queue
 	 * starting to freeze, by dropping the first reference in
-	 * blk_mq_freeze_queue_start, and the moment the last request is
+	 * blk_freeze_queue_start, and the moment the last request is
 	 * consumed, marked by the instant q_usage_counter reaches
 	 * zero.
 	 */
@@ -845,6 +864,8 @@ bool blk_mq_get_driver_tag(struct request *rq, struct blk_mq_hw_ctx **hctx,
 		.flags = wait ? 0 : BLK_MQ_REQ_NOWAIT,
 	};
 
+	might_sleep_if(wait);
+
 	if (rq->tag != -1)
 		goto done;
 
@@ -964,20 +985,12 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list)
 {
 	struct blk_mq_hw_ctx *hctx;
 	struct request *rq;
-	LIST_HEAD(driver_list);
-	struct list_head *dptr;
 	int errors, queued, ret = BLK_MQ_RQ_QUEUE_OK;
 
 	if (list_empty(list))
 		return false;
 
 	/*
-	 * Start off with dptr being NULL, so we start the first request
-	 * immediately, even if we have more pending.
-	 */
-	dptr = NULL;
-
-	/*
 	 * Now process all the entries, sending them to the driver.
 	 */
 	errors = queued = 0;
@@ -993,23 +1006,21 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list)
 			 * The initial allocation attempt failed, so we need to
 			 * rerun the hardware queue when a tag is freed.
 			 */
-			if (blk_mq_dispatch_wait_add(hctx)) {
-				/*
-				 * It's possible that a tag was freed in the
-				 * window between the allocation failure and
-				 * adding the hardware queue to the wait queue.
-				 */
-				if (!blk_mq_get_driver_tag(rq, &hctx, false))
-					break;
-			} else {
+			if (!blk_mq_dispatch_wait_add(hctx))
+				break;
+
+			/*
+			 * It's possible that a tag was freed in the window
+			 * between the allocation failure and adding the
+			 * hardware queue to the wait queue.
+			 */
+			if (!blk_mq_get_driver_tag(rq, &hctx, false))
 				break;
-			}
 		}
 
 		list_del_init(&rq->queuelist);
 
 		bd.rq = rq;
-		bd.list = dptr;
 
 		/*
 		 * Flag last if we have no more requests, or if we have more
@@ -1038,20 +1049,12 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list)
 			pr_err("blk-mq: bad return on queue: %d\n", ret);
 		case BLK_MQ_RQ_QUEUE_ERROR:
 			errors++;
-			rq->errors = -EIO;
-			blk_mq_end_request(rq, rq->errors);
+			blk_mq_end_request(rq, -EIO);
 			break;
 		}
 
 		if (ret == BLK_MQ_RQ_QUEUE_BUSY)
 			break;
-
-		/*
-		 * We've done the first request. If we have more than 1
-		 * left in the list, set dptr to defer issue.
-		 */
-		if (!dptr && list->next != list->prev)
-			dptr = &driver_list;
 	} while (!list_empty(list));
 
 	hctx->dispatched[queued_to_index(queued)]++;
@@ -1062,8 +1065,8 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list)
 	 */
 	if (!list_empty(list)) {
 		/*
-		 * If we got a driver tag for the next request already,
-		 * free it again.
+		 * If an I/O scheduler has been configured and we got a driver
+		 * tag for the next request already, free it again.
 		 */
 		rq = list_first_entry(list, struct request, queuelist);
 		blk_mq_put_driver_tag(rq);
@@ -1073,16 +1076,24 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list)
 		spin_unlock(&hctx->lock);
 
 		/*
-		 * the queue is expected stopped with BLK_MQ_RQ_QUEUE_BUSY, but
-		 * it's possible the queue is stopped and restarted again
-		 * before this. Queue restart will dispatch requests. And since
-		 * requests in rq_list aren't added into hctx->dispatch yet,
-		 * the requests in rq_list might get lost.
+		 * If SCHED_RESTART was set by the caller of this function and
+		 * it is no longer set that means that it was cleared by another
+		 * thread and hence that a queue rerun is needed.
 		 *
-		 * blk_mq_run_hw_queue() already checks the STOPPED bit
+		 * If TAG_WAITING is set that means that an I/O scheduler has
+		 * been configured and another thread is waiting for a driver
+		 * tag. To guarantee fairness, do not rerun this hardware queue
+		 * but let the other thread grab the driver tag.
 		 *
-		 * If RESTART or TAG_WAITING is set, then let completion restart
-		 * the queue instead of potentially looping here.
+		 * If no I/O scheduler has been configured it is possible that
+		 * the hardware queue got stopped and restarted before requests
+		 * were pushed back onto the dispatch list. Rerun the queue to
+		 * avoid starvation. Notes:
+		 * - blk_mq_run_hw_queue() checks whether or not a queue has
+		 *   been stopped before rerunning a queue.
+		 * - Some but not all block drivers stop a queue before
+		 *   returning BLK_MQ_RQ_QUEUE_BUSY. Two exceptions are scsi-mq
+		 *   and dm-rq.
 		 */
 		if (!blk_mq_sched_needs_restart(hctx) &&
 		    !test_bit(BLK_MQ_S_TAG_WAITING, &hctx->state))
@@ -1104,6 +1115,8 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
 		blk_mq_sched_dispatch_requests(hctx);
 		rcu_read_unlock();
 	} else {
+		might_sleep();
+
 		srcu_idx = srcu_read_lock(&hctx->queue_rq_srcu);
 		blk_mq_sched_dispatch_requests(hctx);
 		srcu_read_unlock(&hctx->queue_rq_srcu, srcu_idx);
@@ -1153,13 +1166,9 @@ static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
 		put_cpu();
 	}
 
-	if (msecs == 0)
-		kblockd_schedule_work_on(blk_mq_hctx_next_cpu(hctx),
-					 &hctx->run_work);
-	else
-		kblockd_schedule_delayed_work_on(blk_mq_hctx_next_cpu(hctx),
-						 &hctx->delayed_run_work,
-						 msecs_to_jiffies(msecs));
+	kblockd_schedule_delayed_work_on(blk_mq_hctx_next_cpu(hctx),
+					 &hctx->run_work,
+					 msecs_to_jiffies(msecs));
 }
 
 void blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
@@ -1172,6 +1181,7 @@ void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async)
 {
 	__blk_mq_delay_run_hw_queue(hctx, async, 0);
 }
+EXPORT_SYMBOL(blk_mq_run_hw_queue);
 
 void blk_mq_run_hw_queues(struct request_queue *q, bool async)
 {
@@ -1210,8 +1220,7 @@ EXPORT_SYMBOL(blk_mq_queue_stopped);
 
 void blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx)
 {
-	cancel_work(&hctx->run_work);
-	cancel_delayed_work(&hctx->delay_work);
+	cancel_delayed_work_sync(&hctx->run_work);
 	set_bit(BLK_MQ_S_STOPPED, &hctx->state);
 }
 EXPORT_SYMBOL(blk_mq_stop_hw_queue);
@@ -1268,38 +1277,40 @@ static void blk_mq_run_work_fn(struct work_struct *work)
 {
 	struct blk_mq_hw_ctx *hctx;
 
-	hctx = container_of(work, struct blk_mq_hw_ctx, run_work);
-
-	__blk_mq_run_hw_queue(hctx);
-}
+	hctx = container_of(work, struct blk_mq_hw_ctx, run_work.work);
 
-static void blk_mq_delayed_run_work_fn(struct work_struct *work)
-{
-	struct blk_mq_hw_ctx *hctx;
+	/*
+	 * If we are stopped, don't run the queue. The exception is if
+	 * BLK_MQ_S_START_ON_RUN is set. For that case, we auto-clear
+	 * the STOPPED bit and run it.
+	 */
+	if (test_bit(BLK_MQ_S_STOPPED, &hctx->state)) {
+		if (!test_bit(BLK_MQ_S_START_ON_RUN, &hctx->state))
+			return;
 
-	hctx = container_of(work, struct blk_mq_hw_ctx, delayed_run_work.work);
+		clear_bit(BLK_MQ_S_START_ON_RUN, &hctx->state);
+		clear_bit(BLK_MQ_S_STOPPED, &hctx->state);
+	}
 
 	__blk_mq_run_hw_queue(hctx);
 }
 
-static void blk_mq_delay_work_fn(struct work_struct *work)
-{
-	struct blk_mq_hw_ctx *hctx;
-
-	hctx = container_of(work, struct blk_mq_hw_ctx, delay_work.work);
-
-	if (test_and_clear_bit(BLK_MQ_S_STOPPED, &hctx->state))
-		__blk_mq_run_hw_queue(hctx);
-}
 
 void blk_mq_delay_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
 {
 	if (unlikely(!blk_mq_hw_queue_mapped(hctx)))
 		return;
 
+	/*
+	 * Stop the hw queue, then modify currently delayed work.
+	 * This should prevent us from running the queue prematurely.
+	 * Mark the queue as auto-clearing STOPPED when it runs.
+	 */
 	blk_mq_stop_hw_queue(hctx);
-	kblockd_schedule_delayed_work_on(blk_mq_hctx_next_cpu(hctx),
-			&hctx->delay_work, msecs_to_jiffies(msecs));
+	set_bit(BLK_MQ_S_START_ON_RUN, &hctx->state);
+	kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx),
+					&hctx->run_work,
+					msecs_to_jiffies(msecs));
 }
 EXPORT_SYMBOL(blk_mq_delay_queue);
 
@@ -1408,7 +1419,7 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 
 static void blk_mq_bio_to_request(struct request *rq, struct bio *bio)
 {
-	init_request_from_bio(rq, bio);
+	blk_init_request_from_bio(rq, bio);
 
 	blk_account_io_start(rq, true);
 }
@@ -1453,14 +1464,13 @@ static blk_qc_t request_to_qc_t(struct blk_mq_hw_ctx *hctx, struct request *rq)
 	return blk_tag_to_qc_t(rq->internal_tag, hctx->queue_num, true);
 }
 
-static void blk_mq_try_issue_directly(struct request *rq, blk_qc_t *cookie,
+static void __blk_mq_try_issue_directly(struct request *rq, blk_qc_t *cookie,
 				      bool may_sleep)
 {
 	struct request_queue *q = rq->q;
 	struct blk_mq_queue_data bd = {
 		.rq = rq,
-		.list = NULL,
-		.last = 1
+		.last = true,
 	};
 	struct blk_mq_hw_ctx *hctx;
 	blk_qc_t new_cookie;
@@ -1485,31 +1495,42 @@ static void blk_mq_try_issue_directly(struct request *rq, blk_qc_t *cookie,
 		return;
 	}
 
-	__blk_mq_requeue_request(rq);
-
 	if (ret == BLK_MQ_RQ_QUEUE_ERROR) {
 		*cookie = BLK_QC_T_NONE;
-		rq->errors = -EIO;
-		blk_mq_end_request(rq, rq->errors);
+		blk_mq_end_request(rq, -EIO);
 		return;
 	}
 
+	__blk_mq_requeue_request(rq);
 insert:
 	blk_mq_sched_insert_request(rq, false, true, false, may_sleep);
 }
 
-/*
- * Multiple hardware queue variant. This will not use per-process plugs,
- * but will attempt to bypass the hctx queueing if we can go straight to
- * hardware for SYNC IO.
- */
+static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
+		struct request *rq, blk_qc_t *cookie)
+{
+	if (!(hctx->flags & BLK_MQ_F_BLOCKING)) {
+		rcu_read_lock();
+		__blk_mq_try_issue_directly(rq, cookie, false);
+		rcu_read_unlock();
+	} else {
+		unsigned int srcu_idx;
+
+		might_sleep();
+
+		srcu_idx = srcu_read_lock(&hctx->queue_rq_srcu);
+		__blk_mq_try_issue_directly(rq, cookie, true);
+		srcu_read_unlock(&hctx->queue_rq_srcu, srcu_idx);
+	}
+}
+
 static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 {
 	const int is_sync = op_is_sync(bio->bi_opf);
 	const int is_flush_fua = op_is_flush(bio->bi_opf);
 	struct blk_mq_alloc_data data = { .flags = 0 };
 	struct request *rq;
-	unsigned int request_count = 0, srcu_idx;
+	unsigned int request_count = 0;
 	struct blk_plug *plug;
 	struct request *same_queue_rq = NULL;
 	blk_qc_t cookie;
@@ -1545,147 +1566,21 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 
 	cookie = request_to_qc_t(data.hctx, rq);
 
-	if (unlikely(is_flush_fua)) {
-		if (q->elevator)
-			goto elv_insert;
-		blk_mq_bio_to_request(rq, bio);
-		blk_insert_flush(rq);
-		goto run_queue;
-	}
-
 	plug = current->plug;
-	/*
-	 * If the driver supports defer issued based on 'last', then
-	 * queue it up like normal since we can potentially save some
-	 * CPU this way.
-	 */
-	if (((plug && !blk_queue_nomerges(q)) || is_sync) &&
-	    !(data.hctx->flags & BLK_MQ_F_DEFER_ISSUE)) {
-		struct request *old_rq = NULL;
-
-		blk_mq_bio_to_request(rq, bio);
-
-		/*
-		 * We do limited plugging. If the bio can be merged, do that.
-		 * Otherwise the existing request in the plug list will be
-		 * issued. So the plug list will have one request at most
-		 */
-		if (plug) {
-			/*
-			 * The plug list might get flushed before this. If that
-			 * happens, same_queue_rq is invalid and plug list is
-			 * empty
-			 */
-			if (same_queue_rq && !list_empty(&plug->mq_list)) {
-				old_rq = same_queue_rq;
-				list_del_init(&old_rq->queuelist);
-			}
-			list_add_tail(&rq->queuelist, &plug->mq_list);
-		} else /* is_sync */
-			old_rq = rq;
+	if (unlikely(is_flush_fua)) {
 		blk_mq_put_ctx(data.ctx);
-		if (!old_rq)
-			goto done;
-
-		if (!(data.hctx->flags & BLK_MQ_F_BLOCKING)) {
-			rcu_read_lock();
-			blk_mq_try_issue_directly(old_rq, &cookie, false);
-			rcu_read_unlock();
+		blk_mq_bio_to_request(rq, bio);
+		if (q->elevator) {
+			blk_mq_sched_insert_request(rq, false, true, true,
+					true);
 		} else {
-			srcu_idx = srcu_read_lock(&data.hctx->queue_rq_srcu);
-			blk_mq_try_issue_directly(old_rq, &cookie, true);
-			srcu_read_unlock(&data.hctx->queue_rq_srcu, srcu_idx);
+			blk_insert_flush(rq);
+			blk_mq_run_hw_queue(data.hctx, true);
 		}
-		goto done;
-	}
-
-	if (q->elevator) {
-elv_insert:
-		blk_mq_put_ctx(data.ctx);
-		blk_mq_bio_to_request(rq, bio);
-		blk_mq_sched_insert_request(rq, false, true,
-						!is_sync || is_flush_fua, true);
-		goto done;
-	}
-	if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {
-		/*
-		 * For a SYNC request, send it to the hardware immediately. For
-		 * an ASYNC request, just ensure that we run it later on. The
-		 * latter allows for merging opportunities and more efficient
-		 * dispatching.
-		 */
-run_queue:
-		blk_mq_run_hw_queue(data.hctx, !is_sync || is_flush_fua);
-	}
-	blk_mq_put_ctx(data.ctx);
-done:
-	return cookie;
-}
-
-/*
- * Single hardware queue variant. This will attempt to use any per-process
- * plug for merging and IO deferral.
- */
-static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
-{
-	const int is_sync = op_is_sync(bio->bi_opf);
-	const int is_flush_fua = op_is_flush(bio->bi_opf);
-	struct blk_plug *plug;
-	unsigned int request_count = 0;
-	struct blk_mq_alloc_data data = { .flags = 0 };
-	struct request *rq;
-	blk_qc_t cookie;
-	unsigned int wb_acct;
-
-	blk_queue_bounce(q, &bio);
-
-	if (bio_integrity_enabled(bio) && bio_integrity_prep(bio)) {
-		bio_io_error(bio);
-		return BLK_QC_T_NONE;
-	}
-
-	blk_queue_split(q, &bio, q->bio_split);
-
-	if (!is_flush_fua && !blk_queue_nomerges(q)) {
-		if (blk_attempt_plug_merge(q, bio, &request_count, NULL))
-			return BLK_QC_T_NONE;
-	} else
-		request_count = blk_plug_queued_count(q);
-
-	if (blk_mq_sched_bio_merge(q, bio))
-		return BLK_QC_T_NONE;
-
-	wb_acct = wbt_wait(q->rq_wb, bio, NULL);
-
-	trace_block_getrq(q, bio, bio->bi_opf);
-
-	rq = blk_mq_sched_get_request(q, bio, bio->bi_opf, &data);
-	if (unlikely(!rq)) {
-		__wbt_done(q->rq_wb, wb_acct);
-		return BLK_QC_T_NONE;
-	}
-
-	wbt_track(&rq->issue_stat, wb_acct);
-
-	cookie = request_to_qc_t(data.hctx, rq);
-
-	if (unlikely(is_flush_fua)) {
-		if (q->elevator)
-			goto elv_insert;
-		blk_mq_bio_to_request(rq, bio);
-		blk_insert_flush(rq);
-		goto run_queue;
-	}
-
-	/*
-	 * A task plug currently exists. Since this is completely lockless,
-	 * utilize that to temporarily store requests until the task is
-	 * either done or scheduled away.
-	 */
-	plug = current->plug;
-	if (plug) {
+	} else if (plug && q->nr_hw_queues == 1) {
 		struct request *last = NULL;
 
+		blk_mq_put_ctx(data.ctx);
 		blk_mq_bio_to_request(rq, bio);
 
 		/*
@@ -1694,13 +1589,14 @@ static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
 		 */
 		if (list_empty(&plug->mq_list))
 			request_count = 0;
+		else if (blk_queue_nomerges(q))
+			request_count = blk_plug_queued_count(q);
+
 		if (!request_count)
 			trace_block_plug(q);
 		else
 			last = list_entry_rq(plug->mq_list.prev);
 
-		blk_mq_put_ctx(data.ctx);
-
 		if (request_count >= BLK_MAX_REQUEST_COUNT || (last &&
 		    blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE)) {
 			blk_flush_plug_list(plug, false);
@@ -1708,30 +1604,41 @@ static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
 		}
 
 		list_add_tail(&rq->queuelist, &plug->mq_list);
-		return cookie;
-	}
-
-	if (q->elevator) {
-elv_insert:
-		blk_mq_put_ctx(data.ctx);
+	} else if (plug && !blk_queue_nomerges(q)) {
 		blk_mq_bio_to_request(rq, bio);
-		blk_mq_sched_insert_request(rq, false, true,
-						!is_sync || is_flush_fua, true);
-		goto done;
-	}
-	if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {
+
 		/*
-		 * For a SYNC request, send it to the hardware immediately. For
-		 * an ASYNC request, just ensure that we run it later on. The
-		 * latter allows for merging opportunities and more efficient
-		 * dispatching.
+		 * We do limited plugging. If the bio can be merged, do that.
+		 * Otherwise the existing request in the plug list will be
+		 * issued. So the plug list will have one request at most
+		 * The plug list might get flushed before this. If that happens,
+		 * the plug list is empty, and same_queue_rq is invalid.
 		 */
-run_queue:
-		blk_mq_run_hw_queue(data.hctx, !is_sync || is_flush_fua);
-	}
+		if (list_empty(&plug->mq_list))
+			same_queue_rq = NULL;
+		if (same_queue_rq)
+			list_del_init(&same_queue_rq->queuelist);
+		list_add_tail(&rq->queuelist, &plug->mq_list);
+
+		blk_mq_put_ctx(data.ctx);
+
+		if (same_queue_rq)
+			blk_mq_try_issue_directly(data.hctx, same_queue_rq,
+					&cookie);
+	} else if (q->nr_hw_queues > 1 && is_sync) {
+		blk_mq_put_ctx(data.ctx);
+		blk_mq_bio_to_request(rq, bio);
+		blk_mq_try_issue_directly(data.hctx, rq, &cookie);
+	} else if (q->elevator) {
+		blk_mq_put_ctx(data.ctx);
+		blk_mq_bio_to_request(rq, bio);
+		blk_mq_sched_insert_request(rq, false, true, true, true);
+	} else if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {
+		blk_mq_put_ctx(data.ctx);
+		blk_mq_run_hw_queue(data.hctx, true);
+	} else
+		blk_mq_put_ctx(data.ctx);
 
-	blk_mq_put_ctx(data.ctx);
-done:
 	return cookie;
 }
 
@@ -1988,9 +1895,7 @@ static int blk_mq_init_hctx(struct request_queue *q,
 	if (node == NUMA_NO_NODE)
 		node = hctx->numa_node = set->numa_node;
 
-	INIT_WORK(&hctx->run_work, blk_mq_run_work_fn);
-	INIT_DELAYED_WORK(&hctx->delayed_run_work, blk_mq_delayed_run_work_fn);
-	INIT_DELAYED_WORK(&hctx->delay_work, blk_mq_delay_work_fn);
+	INIT_DELAYED_WORK(&hctx->run_work, blk_mq_run_work_fn);
 	spin_lock_init(&hctx->lock);
 	INIT_LIST_HEAD(&hctx->dispatch);
 	hctx->queue = q;
@@ -2067,8 +1972,6 @@ static void blk_mq_init_cpu_queues(struct request_queue *q,
 		spin_lock_init(&__ctx->lock);
 		INIT_LIST_HEAD(&__ctx->rq_list);
 		__ctx->queue = q;
-		blk_stat_init(&__ctx->stat[BLK_STAT_READ]);
-		blk_stat_init(&__ctx->stat[BLK_STAT_WRITE]);
 
 		/* If the cpu isn't online, the cpu is mapped to first hctx */
 		if (!cpu_online(i))
@@ -2215,6 +2118,8 @@ static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set, bool shared)
 {
 	struct request_queue *q;
 
+	lockdep_assert_held(&set->tag_list_lock);
+
 	list_for_each_entry(q, &set->tag_list, tag_set_list) {
 		blk_mq_freeze_queue(q);
 		queue_set_hctx_shared(q, shared);
@@ -2227,7 +2132,8 @@ static void blk_mq_del_queue_tag_set(struct request_queue *q)
 	struct blk_mq_tag_set *set = q->tag_set;
 
 	mutex_lock(&set->tag_list_lock);
-	list_del_init(&q->tag_set_list);
+	list_del_rcu(&q->tag_set_list);
+	INIT_LIST_HEAD(&q->tag_set_list);
 	if (list_is_singular(&set->tag_list)) {
 		/* just transitioned to unshared */
 		set->flags &= ~BLK_MQ_F_TAG_SHARED;
@@ -2235,6 +2141,8 @@ static void blk_mq_del_queue_tag_set(struct request_queue *q)
 		blk_mq_update_tag_set_depth(set, false);
 	}
 	mutex_unlock(&set->tag_list_lock);
+
+	synchronize_rcu();
 }
 
 static void blk_mq_add_queue_tag_set(struct blk_mq_tag_set *set,
@@ -2252,7 +2160,7 @@ static void blk_mq_add_queue_tag_set(struct blk_mq_tag_set *set,
 	}
 	if (set->flags & BLK_MQ_F_TAG_SHARED)
 		queue_set_hctx_shared(q, true);
-	list_add_tail(&q->tag_set_list, &set->tag_list);
+	list_add_tail_rcu(&q->tag_set_list, &set->tag_list);
 
 	mutex_unlock(&set->tag_list_lock);
 }
@@ -2364,6 +2272,12 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 	/* mark the queue as mq asap */
 	q->mq_ops = set->ops;
 
+	q->poll_cb = blk_stat_alloc_callback(blk_mq_poll_stats_fn,
+					     blk_mq_poll_stats_bkt,
+					     BLK_MQ_POLL_STATS_BKTS, q);
+	if (!q->poll_cb)
+		goto err_exit;
+
 	q->queue_ctx = alloc_percpu(struct blk_mq_ctx);
 	if (!q->queue_ctx)
 		goto err_exit;
@@ -2398,10 +2312,7 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 	INIT_LIST_HEAD(&q->requeue_list);
 	spin_lock_init(&q->requeue_lock);
 
-	if (q->nr_hw_queues > 1)
-		blk_queue_make_request(q, blk_mq_make_request);
-	else
-		blk_queue_make_request(q, blk_sq_make_request);
+	blk_queue_make_request(q, blk_mq_make_request);
 
 	/*
 	 * Do this after blk_queue_make_request() overrides it...
@@ -2456,8 +2367,6 @@ void blk_mq_free_queue(struct request_queue *q)
 	list_del_init(&q->all_q_node);
 	mutex_unlock(&all_q_mutex);
 
-	wbt_exit(q);
-
 	blk_mq_del_queue_tag_set(q);
 
 	blk_mq_exit_hw_queues(q, set, set->nr_hw_queues);
@@ -2502,7 +2411,7 @@ static void blk_mq_queue_reinit_work(void)
 	 * take place in parallel.
 	 */
 	list_for_each_entry(q, &all_q_list, all_q_node)
-		blk_mq_freeze_queue_start(q);
+		blk_freeze_queue_start(q);
 	list_for_each_entry(q, &all_q_list, all_q_node)
 		blk_mq_freeze_queue_wait(q);
 
@@ -2743,6 +2652,8 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)
 {
 	struct request_queue *q;
 
+	lockdep_assert_held(&set->tag_list_lock);
+
 	if (nr_hw_queues > nr_cpu_ids)
 		nr_hw_queues = nr_cpu_ids;
 	if (nr_hw_queues < 1 || nr_hw_queues == set->nr_hw_queues)
@@ -2755,16 +2666,6 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)
 	blk_mq_update_queue_map(set);
 	list_for_each_entry(q, &set->tag_list, tag_set_list) {
 		blk_mq_realloc_hw_ctxs(set, q);
-
-		/*
-		 * Manually set the make_request_fn as blk_queue_make_request
-		 * resets a lot of the queue settings.
-		 */
-		if (q->nr_hw_queues > 1)
-			q->make_request_fn = blk_mq_make_request;
-		else
-			q->make_request_fn = blk_sq_make_request;
-
 		blk_mq_queue_reinit(q, cpu_online_mask);
 	}
 
@@ -2773,39 +2674,69 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)
 }
 EXPORT_SYMBOL_GPL(blk_mq_update_nr_hw_queues);
 
+/* Enable polling stats and return whether they were already enabled. */
+static bool blk_poll_stats_enable(struct request_queue *q)
+{
+	if (test_bit(QUEUE_FLAG_POLL_STATS, &q->queue_flags) ||
+	    test_and_set_bit(QUEUE_FLAG_POLL_STATS, &q->queue_flags))
+		return true;
+	blk_stat_add_callback(q, q->poll_cb);
+	return false;
+}
+
+static void blk_mq_poll_stats_start(struct request_queue *q)
+{
+	/*
+	 * We don't arm the callback if polling stats are not enabled or the
+	 * callback is already active.
+	 */
+	if (!test_bit(QUEUE_FLAG_POLL_STATS, &q->queue_flags) ||
+	    blk_stat_is_active(q->poll_cb))
+		return;
+
+	blk_stat_activate_msecs(q->poll_cb, 100);
+}
+
+static void blk_mq_poll_stats_fn(struct blk_stat_callback *cb)
+{
+	struct request_queue *q = cb->data;
+	int bucket;
+
+	for (bucket = 0; bucket < BLK_MQ_POLL_STATS_BKTS; bucket++) {
+		if (cb->stat[bucket].nr_samples)
+			q->poll_stat[bucket] = cb->stat[bucket];
+	}
+}
+
 static unsigned long blk_mq_poll_nsecs(struct request_queue *q,
 				       struct blk_mq_hw_ctx *hctx,
 				       struct request *rq)
 {
-	struct blk_rq_stat stat[2];
 	unsigned long ret = 0;
+	int bucket;
 
 	/*
 	 * If stats collection isn't on, don't sleep but turn it on for
 	 * future users
 	 */
-	if (!blk_stat_enable(q))
+	if (!blk_poll_stats_enable(q))
 		return 0;
 
 	/*
-	 * We don't have to do this once per IO, should optimize this
-	 * to just use the current window of stats until it changes
-	 */
-	memset(&stat, 0, sizeof(stat));
-	blk_hctx_stat_get(hctx, stat);
-
-	/*
 	 * As an optimistic guess, use half of the mean service time
 	 * for this type of request. We can (and should) make this smarter.
 	 * For instance, if the completion latencies are tight, we can
 	 * get closer than just half the mean. This is especially
 	 * important on devices where the completion latencies are longer
-	 * than ~10 usec.
+	 * than ~10 usec. We do use the stats for the relevant IO size
+	 * if available which does lead to better estimates.
 	 */
-	if (req_op(rq) == REQ_OP_READ && stat[BLK_STAT_READ].nr_samples)
-		ret = (stat[BLK_STAT_READ].mean + 1) / 2;
-	else if (req_op(rq) == REQ_OP_WRITE && stat[BLK_STAT_WRITE].nr_samples)
-		ret = (stat[BLK_STAT_WRITE].mean + 1) / 2;
+	bucket = blk_mq_poll_stats_bkt(rq);
+	if (bucket < 0)
+		return ret;
+
+	if (q->poll_stat[bucket].nr_samples)
+		ret = (q->poll_stat[bucket].mean + 1) / 2;
 
 	return ret;
 }