[PATCHv5 4/5] block: use {alloc|free}_sched data methods

[Nilay Shroff <nilay@linux.ibm.com>]

The previous patch introduced ->alloc_sched_data and
->free_sched_data methods. This patch builds upon that
by now using these methods during elevator switch and
nr_hw_queue update.

It's also ensured that scheduler-specific data is
allocated and freed through the new callbacks outside
of the ->freeze_lock and ->elevator_lock locking contexts,
thereby preventing any dependency on pcpu_alloc_mutex.

Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
---
 block/blk-mq-sched.c | 27 +++++++++++++++++++++------
 block/blk-mq-sched.h |  5 ++++-
 block/elevator.c     | 34 ++++++++++++++++++++++------------
 block/elevator.h     |  4 +++-
 4 files changed, 50 insertions(+), 20 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 03ff16c49976..95ee2cb7aee4 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -428,12 +428,17 @@ void blk_mq_free_sched_tags(struct elevator_tags *et,
 }
 
 void blk_mq_free_sched_res(struct elevator_resources *res,
+		struct elevator_type *type,
 		struct blk_mq_tag_set *set)
 {
 	if (res->et) {
 		blk_mq_free_sched_tags(res->et, set);
 		res->et = NULL;
 	}
+	if (res->data) {
+		blk_mq_free_sched_data(type, res->data);
+		res->data = NULL;
+	}
 }
 
 void blk_mq_free_sched_res_batch(struct xarray *elv_tbl,
@@ -458,7 +463,7 @@ void blk_mq_free_sched_res_batch(struct xarray *elv_tbl,
 				WARN_ON_ONCE(1);
 				continue;
 			}
-			blk_mq_free_sched_res(&ctx->res, set);
+			blk_mq_free_sched_res(&ctx->res, ctx->type, set);
 		}
 	}
 }
@@ -541,7 +546,9 @@ struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
 }
 
 int blk_mq_alloc_sched_res(struct request_queue *q,
-		struct elevator_resources *res, unsigned int nr_hw_queues)
+		struct elevator_type *type,
+		struct elevator_resources *res,
+		unsigned int nr_hw_queues)
 {
 	struct blk_mq_tag_set *set = q->tag_set;
 
@@ -550,6 +557,12 @@ int blk_mq_alloc_sched_res(struct request_queue *q,
 	if (!res->et)
 		return -ENOMEM;
 
+	res->data = blk_mq_alloc_sched_data(q, type);
+	if (!res->data) {
+		blk_mq_free_sched_tags(res->et, set);
+		return -ENOMEM;
+	}
+
 	return 0;
 }
 
@@ -577,19 +590,21 @@ int blk_mq_alloc_sched_res_batch(struct xarray *elv_tbl,
 				goto out_unwind;
 			}
 
-			ret = blk_mq_alloc_sched_res(q, &ctx->res,
-					nr_hw_queues);
+			ret = blk_mq_alloc_sched_res(q, q->elevator->type,
+					&ctx->res, nr_hw_queues);
 			if (ret)
 				goto out_unwind;
 		}
 	}
 	return 0;
+
 out_unwind:
 	list_for_each_entry_continue_reverse(q, &set->tag_list, tag_set_list) {
 		if (q->elevator) {
 			ctx = xa_load(elv_tbl, q->id);
 			if (ctx)
-				blk_mq_free_sched_res(&ctx->res, set);
+				blk_mq_free_sched_res(&ctx->res,
+						ctx->type, set);
 		}
 	}
 	return ret;
@@ -606,7 +621,7 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e,
 	unsigned long i;
 	int ret;
 
-	eq = elevator_alloc(q, e, et);
+	eq = elevator_alloc(q, e, res);
 	if (!eq)
 		return -ENOMEM;
 
diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
index 3ac64b66176a..4387a29545f5 100644
--- a/block/blk-mq-sched.h
+++ b/block/blk-mq-sched.h
@@ -26,7 +26,9 @@ void blk_mq_sched_free_rqs(struct request_queue *q);
 struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
 		unsigned int nr_hw_queues, unsigned int nr_requests);
 int blk_mq_alloc_sched_res(struct request_queue *q,
-		struct elevator_resources *res, unsigned int nr_hw_queues);
+		struct elevator_type *type,
+		struct elevator_resources *res,
+		unsigned int nr_hw_queues);
 int blk_mq_alloc_sched_res_batch(struct xarray *elv_tbl,
 		struct blk_mq_tag_set *set, unsigned int nr_hw_queues);
 int blk_mq_alloc_sched_ctx_batch(struct xarray *elv_tbl,
@@ -35,6 +37,7 @@ void blk_mq_free_sched_ctx_batch(struct xarray *elv_tbl);
 void blk_mq_free_sched_tags(struct elevator_tags *et,
 		struct blk_mq_tag_set *set);
 void blk_mq_free_sched_res(struct elevator_resources *res,
+		struct elevator_type *type,
 		struct blk_mq_tag_set *set);
 void blk_mq_free_sched_res_batch(struct xarray *et_table,
 		struct blk_mq_tag_set *set);
diff --git a/block/elevator.c b/block/elevator.c
index cbec292a4af5..5b37ef44f52d 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -121,7 +121,7 @@ static struct elevator_type *elevator_find_get(const char *name)
 static const struct kobj_type elv_ktype;
 
 struct elevator_queue *elevator_alloc(struct request_queue *q,
-		struct elevator_type *e, struct elevator_tags *et)
+		struct elevator_type *e, struct elevator_resources *res)
 {
 	struct elevator_queue *eq;
 
@@ -134,7 +134,8 @@ struct elevator_queue *elevator_alloc(struct request_queue *q,
 	kobject_init(&eq->kobj, &elv_ktype);
 	mutex_init(&eq->sysfs_lock);
 	hash_init(eq->hash);
-	eq->et = et;
+	eq->et = res->et;
+	eq->elevator_data = res->data;
 
 	return eq;
 }
@@ -617,7 +618,7 @@ static void elv_exit_and_release(struct elv_change_ctx *ctx,
 	mutex_unlock(&q->elevator_lock);
 	blk_mq_unfreeze_queue(q, memflags);
 	if (e) {
-		blk_mq_free_sched_res(&ctx->res, q->tag_set);
+		blk_mq_free_sched_res(&ctx->res, ctx->type, q->tag_set);
 		kobject_put(&e->kobj);
 	}
 }
@@ -628,12 +629,15 @@ static int elevator_change_done(struct request_queue *q,
 	int ret = 0;
 
 	if (ctx->old) {
-		struct elevator_resources res = {.et = ctx->old->et};
+		struct elevator_resources res = {
+			.et = ctx->old->et,
+			.data = ctx->old->elevator_data
+		};
 		bool enable_wbt = test_bit(ELEVATOR_FLAG_ENABLE_WBT_ON_EXIT,
 				&ctx->old->flags);
 
 		elv_unregister_queue(q, ctx->old);
-		blk_mq_free_sched_res(&res, q->tag_set);
+		blk_mq_free_sched_res(&res, ctx->old->type, q->tag_set);
 		kobject_put(&ctx->old->kobj);
 		if (enable_wbt)
 			wbt_enable_default(q->disk);
@@ -658,7 +662,8 @@ static int elevator_change(struct request_queue *q, struct elv_change_ctx *ctx)
 	lockdep_assert_held(&set->update_nr_hwq_lock);
 
 	if (strncmp(ctx->name, "none", 4)) {
-		ret = blk_mq_alloc_sched_res(q, &ctx->res, set->nr_hw_queues);
+		ret = blk_mq_alloc_sched_res(q, ctx->type, &ctx->res,
+				set->nr_hw_queues);
 		if (ret)
 			return ret;
 	}
@@ -681,11 +686,12 @@ static int elevator_change(struct request_queue *q, struct elv_change_ctx *ctx)
 	blk_mq_unfreeze_queue(q, memflags);
 	if (!ret)
 		ret = elevator_change_done(q, ctx);
+
 	/*
 	 * Free sched resource if it's allocated but we couldn't switch elevator.
 	 */
 	if (!ctx->new)
-		blk_mq_free_sched_res(&ctx->res, set);
+		blk_mq_free_sched_res(&ctx->res, ctx->type, set);
 
 	return ret;
 }
@@ -711,11 +717,12 @@ void elv_update_nr_hw_queues(struct request_queue *q,
 	blk_mq_unfreeze_queue_nomemrestore(q);
 	if (!ret)
 		WARN_ON_ONCE(elevator_change_done(q, ctx));
+
 	/*
 	 * Free sched resource if it's allocated but we couldn't switch elevator.
 	 */
 	if (!ctx->new)
-		blk_mq_free_sched_res(&ctx->res, set);
+		blk_mq_free_sched_res(&ctx->res, ctx->type, set);
 }
 
 /*
@@ -729,7 +736,6 @@ void elevator_set_default(struct request_queue *q)
 		.no_uevent = true,
 	};
 	int err;
-	struct elevator_type *e;
 
 	/* now we allow to switch elevator */
 	blk_queue_flag_clear(QUEUE_FLAG_NO_ELV_SWITCH, q);
@@ -742,8 +748,8 @@ void elevator_set_default(struct request_queue *q)
 	 * have multiple queues or mq-deadline is not available, default
 	 * to "none".
 	 */
-	e = elevator_find_get(ctx.name);
-	if (!e)
+	ctx.type = elevator_find_get(ctx.name);
+	if (!ctx.type)
 		return;
 
 	if ((q->nr_hw_queues == 1 ||
@@ -753,7 +759,7 @@ void elevator_set_default(struct request_queue *q)
 			pr_warn("\"%s\" elevator initialization, failed %d, falling back to \"none\"\n",
 					ctx.name, err);
 	}
-	elevator_put(e);
+	elevator_put(ctx.type);
 }
 
 void elevator_set_none(struct request_queue *q)
@@ -802,6 +808,7 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
 	ctx.name = strstrip(elevator_name);
 
 	elv_iosched_load_module(ctx.name);
+	ctx.type = elevator_find_get(ctx.name);
 
 	down_read(&set->update_nr_hwq_lock);
 	if (!blk_queue_no_elv_switch(q)) {
@@ -812,6 +819,9 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
 		ret = -ENOENT;
 	}
 	up_read(&set->update_nr_hwq_lock);
+
+	if (ctx.type)
+		elevator_put(ctx.type);
 	return ret;
 }
 
diff --git a/block/elevator.h b/block/elevator.h
index e34043f6da26..3ee1d494f48a 100644
--- a/block/elevator.h
+++ b/block/elevator.h
@@ -33,6 +33,8 @@ struct elevator_tags {
 };
 
 struct elevator_resources {
+	/* holds elevator data */
+	void *data;
 	/* holds elevator tags */
 	struct elevator_tags *et;
 };
@@ -185,7 +187,7 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *page, size_t count);
 
 extern bool elv_bio_merge_ok(struct request *, struct bio *);
 struct elevator_queue *elevator_alloc(struct request_queue *,
-		struct elevator_type *, struct elevator_tags *);
+		struct elevator_type *, struct elevator_resources *);
 
 /*
  * Helper functions.
-- 
2.51.0