[PATCH V2 1/2] blk-mq: init hctx sched after update ctx and hctx mapping

[Jianchao Wang]

Currently, when update nr_hw_queues, io scheduler's init_hctx will
be invoked before the mapping between ctx and hctx is adapted
correctly by blk_mq_map_swqueue. The io scheduler init_hctx (kyber)
may depend on this mapping and get wrong result and panic finally.
A simply way to fix this is switch the io scheduler to none before
update the nr_hw_queues, and then get it back after update nr_hw_queues.
To achieve this, we add a new member elv_type in request_queue to
save the original elevator and adapt and export elevator_switch_mq.
And also blk_mq_sched_init_/exit_hctx are removed due to nobody use
them any more.

Signed-off-by: Jianchao Wang <jianchao.w.wang@xxxxxxxxxx>
---
 block/blk-mq-sched.c   | 44 --------------------------------------------
 block/blk-mq-sched.h   |  5 -----
 block/blk-mq.c         | 36 ++++++++++++++++++++++++++++--------
 block/blk.h            |  2 ++
 block/elevator.c       | 20 ++++++++++++--------
 include/linux/blkdev.h |  3 +++
 6 files changed, 45 insertions(+), 65 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index cf9c66c..29bfe80 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -462,50 +462,6 @@ static void blk_mq_sched_tags_teardown(struct request_queue *q)
 		blk_mq_sched_free_tags(set, hctx, i);
 }
 
-int blk_mq_sched_init_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
-			   unsigned int hctx_idx)
-{
-	struct elevator_queue *e = q->elevator;
-	int ret;
-
-	if (!e)
-		return 0;
-
-	ret = blk_mq_sched_alloc_tags(q, hctx, hctx_idx);
-	if (ret)
-		return ret;
-
-	if (e->type->ops.mq.init_hctx) {
-		ret = e->type->ops.mq.init_hctx(hctx, hctx_idx);
-		if (ret) {
-			blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
-			return ret;
-		}
-	}
-
-	blk_mq_debugfs_register_sched_hctx(q, hctx);
-
-	return 0;
-}
-
-void blk_mq_sched_exit_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
-			    unsigned int hctx_idx)
-{
-	struct elevator_queue *e = q->elevator;
-
-	if (!e)
-		return;
-
-	blk_mq_debugfs_unregister_sched_hctx(hctx);
-
-	if (e->type->ops.mq.exit_hctx && hctx->sched_data) {
-		e->type->ops.mq.exit_hctx(hctx, hctx_idx);
-		hctx->sched_data = NULL;
-	}
-
-	blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
-}
-
 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 {
 	struct blk_mq_hw_ctx *hctx;
diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
index 0cb8f93..4e028ee 100644
--- a/block/blk-mq-sched.h
+++ b/block/blk-mq-sched.h
@@ -28,11 +28,6 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx);
 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e);
 void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e);
 
-int blk_mq_sched_init_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
-			   unsigned int hctx_idx);
-void blk_mq_sched_exit_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
-			    unsigned int hctx_idx);
-
 static inline bool
 blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
 {
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 5efd789..de7027f 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2147,8 +2147,6 @@ static void blk_mq_exit_hctx(struct request_queue *q,
 	if (set->ops->exit_request)
 		set->ops->exit_request(set, hctx->fq->flush_rq, hctx_idx);
 
-	blk_mq_sched_exit_hctx(q, hctx, hctx_idx);
-
 	if (set->ops->exit_hctx)
 		set->ops->exit_hctx(hctx, hctx_idx);
 
@@ -2216,12 +2214,9 @@ static int blk_mq_init_hctx(struct request_queue *q,
 	    set->ops->init_hctx(hctx, set->driver_data, hctx_idx))
 		goto free_bitmap;
 
-	if (blk_mq_sched_init_hctx(q, hctx, hctx_idx))
-		goto exit_hctx;
-
 	hctx->fq = blk_alloc_flush_queue(q, hctx->numa_node, set->cmd_size);
 	if (!hctx->fq)
-		goto sched_exit_hctx;
+		goto exit_hctx;
 
 	if (blk_mq_init_request(set, hctx->fq->flush_rq, hctx_idx, node))
 		goto free_fq;
@@ -2235,8 +2230,6 @@ static int blk_mq_init_hctx(struct request_queue *q,
 
  free_fq:
 	kfree(hctx->fq);
- sched_exit_hctx:
-	blk_mq_sched_exit_hctx(q, hctx, hctx_idx);
  exit_hctx:
 	if (set->ops->exit_hctx)
 		set->ops->exit_hctx(hctx, hctx_idx);
@@ -2913,6 +2906,25 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
 	list_for_each_entry(q, &set->tag_list, tag_set_list)
 		blk_mq_freeze_queue(q);
 
+	/*
+	 * switch io scheduler to NULL to clean up the data in it.
+	 * will get it back after update mapping between cpu and hw queues.
+	 */
+	list_for_each_entry(q, &set->tag_list, tag_set_list) {
+		if (!q->elevator) {
+			q->elv_type = NULL;
+			continue;
+		}
+		q->elv_type = q->elevator->type;
+		mutex_lock(&q->sysfs_lock);
+		/*
+		 * elevator_release will put it.
+		 */
+		__module_get(q->elv_type->elevator_owner);
+		elevator_switch_mq(q, NULL);
+		mutex_unlock(&q->sysfs_lock);
+	}
+
 	set->nr_hw_queues = nr_hw_queues;
 	blk_mq_update_queue_map(set);
 	list_for_each_entry(q, &set->tag_list, tag_set_list) {
@@ -2920,6 +2932,14 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
 		blk_mq_queue_reinit(q);
 	}
 
+	list_for_each_entry(q, &set->tag_list, tag_set_list) {
+		if (!q->elv_type)
+			continue;
+
+		mutex_lock(&q->sysfs_lock);
+		elevator_switch_mq(q, q->elv_type);
+		mutex_unlock(&q->sysfs_lock);
+	}
 	list_for_each_entry(q, &set->tag_list, tag_set_list)
 		blk_mq_unfreeze_queue(q);
 }
diff --git a/block/blk.h b/block/blk.h
index d4d67e9..0c9bc8d 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -234,6 +234,8 @@ static inline void elv_deactivate_rq(struct request_queue *q, struct request *rq
 
 int elevator_init(struct request_queue *);
 int elevator_init_mq(struct request_queue *q);
+int elevator_switch_mq(struct request_queue *q,
+			      struct elevator_type *new_e);
 void elevator_exit(struct request_queue *, struct elevator_queue *);
 int elv_register_queue(struct request_queue *q);
 void elv_unregister_queue(struct request_queue *q);
diff --git a/block/elevator.c b/block/elevator.c
index fa828b5..5ea6e7d 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -933,16 +933,13 @@ void elv_unregister(struct elevator_type *e)
 }
 EXPORT_SYMBOL_GPL(elv_unregister);
 
-static int elevator_switch_mq(struct request_queue *q,
+int elevator_switch_mq(struct request_queue *q,
 			      struct elevator_type *new_e)
 {
 	int ret;
 
 	lockdep_assert_held(&q->sysfs_lock);
 
-	blk_mq_freeze_queue(q);
-	blk_mq_quiesce_queue(q);
-
 	if (q->elevator) {
 		if (q->elevator->registered)
 			elv_unregister_queue(q);
@@ -968,8 +965,6 @@ static int elevator_switch_mq(struct request_queue *q,
 		blk_add_trace_msg(q, "elv switch: none");
 
 out:
-	blk_mq_unquiesce_queue(q);
-	blk_mq_unfreeze_queue(q);
 	return ret;
 }
 
@@ -1021,8 +1016,17 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 
 	lockdep_assert_held(&q->sysfs_lock);
 
-	if (q->mq_ops)
-		return elevator_switch_mq(q, new_e);
+	if (q->mq_ops) {
+		blk_mq_freeze_queue(q);
+		blk_mq_quiesce_queue(q);
+
+		err = elevator_switch_mq(q, new_e);
+
+		blk_mq_unquiesce_queue(q);
+		blk_mq_unfreeze_queue(q);
+
+		return err;
+	}
 
 	/*
 	 * Turn on BYPASS and drain all requests w/ elevator private data.
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index d6869e0..ee930c4 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -437,6 +437,9 @@ struct request_queue {
 	struct list_head	queue_head;
 	struct request		*last_merge;
 	struct elevator_queue	*elevator;
+
+	/* used when update nr_hw_queues */
+	struct elevator_type	*elv_type;
 	int			nr_rqs[2];	/* # allocated [a]sync rqs */
 	int			nr_rqs_elvpriv;	/* # allocated rqs w/ elvpriv */
 
-- 
2.7.4