block: move sched debugfs register into elvevator_register_queue

JIRA: https://issues.redhat.com/browse/RHEL-106845

commit 92c22d7
Author: Ming Lei <ming.lei@redhat.com>
Date:   Mon May 5 22:17:44 2025 +0800

    block: move sched debugfs register into elvevator_register_queue

    sched debugfs shares same lifetime with scheduler's kobject, and same
    lock(elevator lock), so move sched debugfs register/unregister into
    elevator_register_queue() and elevator_unregister_queue().

    Then we needn't blk_mq_debugfs_register() for us to register sched
    debugfs any more.

    Reviewed-by: Yu Kuai <yukuai3@huawei.com>
    Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Reviewed-by: Hannes Reinecke <hare@suse.de>
    Signed-off-by: Ming Lei <ming.lei@redhat.com>
    Link: https://lore.kernel.org/r/20250505141805.2751237-7-ming.lei@redhat.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Author: Ming Lei

block/blk-mq-debugfs.c

@@ -625,20 +625,9 @@ void blk_mq_debugfs_register(struct request_queue *q)
 
 	debugfs_create_files(q->debugfs_dir, q, blk_mq_debugfs_queue_attrs);
 
-	/*
-	 * blk_mq_init_sched() attempted to do this already, but q->debugfs_dir
-	 * didn't exist yet (because we don't know what to name the directory
-	 * until the queue is registered to a gendisk).
-	 */
-	if (q->elevator && !q->sched_debugfs_dir)
-		blk_mq_debugfs_register_sched(q);
-
-	/* Similarly, blk_mq_init_hctx() couldn't do this previously. */
 	queue_for_each_hw_ctx(q, hctx, i) {
 		if (!hctx->debugfs_dir)
 			blk_mq_debugfs_register_hctx(q, hctx);
-		if (q->elevator && !hctx->sched_debugfs_dir)
-			blk_mq_debugfs_register_sched_hctx(q, hctx);
 	}
 
 	if (q->rq_qos) {

block/blk-mq-sched.c

@@ -434,7 +434,7 @@ static int blk_mq_init_sched_shared_tags(struct request_queue *queue)
 	return 0;
 }
 
-static void blk_mq_sched_reg_debugfs(struct request_queue *q)
+void blk_mq_sched_reg_debugfs(struct request_queue *q)
 {
 	struct blk_mq_hw_ctx *hctx;
 	unsigned long i;
@@ -446,7 +446,7 @@ static void blk_mq_sched_reg_debugfs(struct request_queue *q)
 	mutex_unlock(&q->debugfs_mutex);
 }
 
-static void blk_mq_sched_unreg_debugfs(struct request_queue *q)
+void blk_mq_sched_unreg_debugfs(struct request_queue *q)
 {
 	struct blk_mq_hw_ctx *hctx;
 	unsigned long i;
@@ -503,10 +503,6 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 			}
 		}
 	}
-
-	/* sched is initialized, it is ready to export it via debugfs */
-	blk_mq_sched_reg_debugfs(q);
-
 	return 0;
 
 err_free_map_and_rqs:
@@ -544,9 +540,6 @@ void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
 	unsigned long i;
 	unsigned int flags = 0;
 
-	/* unexport via debugfs before exiting sched */
-	blk_mq_sched_unreg_debugfs(q);
-
 	queue_for_each_hw_ctx(q, hctx, i) {
 		if (e->type->ops.exit_hctx && hctx->sched_data) {
 			e->type->ops.exit_hctx(hctx, i);

block/elevator.c

@@ -472,6 +472,11 @@ int elv_register_queue(struct request_queue *q, bool uevent)
 		if (uevent)
 			kobject_uevent(&e->kobj, KOBJ_ADD);
 
+		/*
+		 * Sched is initialized, it is ready to export it via
+		 * debugfs
+		 */
+		blk_mq_sched_reg_debugfs(q);
 		set_bit(ELEVATOR_FLAG_REGISTERED, &e->flags);
 	}
 	return error;
@@ -486,6 +491,9 @@ void elv_unregister_queue(struct request_queue *q)
 	if (e && test_and_clear_bit(ELEVATOR_FLAG_REGISTERED, &e->flags)) {
 		kobject_uevent(&e->kobj, KOBJ_REMOVE);
 		kobject_del(&e->kobj);
+
+		/* unexport via debugfs before exiting sched */
+		blk_mq_sched_unreg_debugfs(q);
 	}
 }
 

block/elevator.h

@@ -181,4 +181,7 @@ extern struct request *elv_rb_find(struct rb_root *, sector_t);
 #define rq_entry_fifo(ptr)	list_entry((ptr), struct request, queuelist)
 #define rq_fifo_clear(rq)	list_del_init(&(rq)->queuelist)
 
+void blk_mq_sched_reg_debugfs(struct request_queue *q);
+void blk_mq_sched_unreg_debugfs(struct request_queue *q);
+
 #endif /* _ELEVATOR_H */