block: add two helpers for registering/un-registering sched debugfs

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

commit ed3896a
Author: Ming Lei <ming.lei@redhat.com>
Date:   Mon May 5 22:17:43 2025 +0800

    block: add two helpers for registering/un-registering sched debugfs

    Add blk_mq_sched_reg_debugfs()/blk_mq_sched_unreg_debugfs() to clean up
    sched init/exit code a bit.

    Register & unregister debugfs for sched & sched_hctx order is changed a
    bit, but it is safe because sched & sched_hctx is guaranteed to be ready
    when exporting via debugfs.

    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/20250505141805.2751237-6-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-sched.c

@@ -434,6 +434,30 @@ 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)
+{
+	struct blk_mq_hw_ctx *hctx;
+	unsigned long i;
+
+	mutex_lock(&q->debugfs_mutex);
+	blk_mq_debugfs_register_sched(q);
+	queue_for_each_hw_ctx(q, hctx, i)
+		blk_mq_debugfs_register_sched_hctx(q, hctx);
+	mutex_unlock(&q->debugfs_mutex);
+}
+
+static void blk_mq_sched_unreg_debugfs(struct request_queue *q)
+{
+	struct blk_mq_hw_ctx *hctx;
+	unsigned long i;
+
+	mutex_lock(&q->debugfs_mutex);
+	queue_for_each_hw_ctx(q, hctx, i)
+		blk_mq_debugfs_unregister_sched_hctx(hctx);
+	blk_mq_debugfs_unregister_sched(q);
+	mutex_unlock(&q->debugfs_mutex);
+}
+
 /* caller must have a reference to @e, will grab another one if successful */
 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 {
@@ -467,10 +491,6 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 	if (ret)
 		goto err_free_map_and_rqs;
 
-	mutex_lock(&q->debugfs_mutex);
-	blk_mq_debugfs_register_sched(q);
-	mutex_unlock(&q->debugfs_mutex);
-
 	queue_for_each_hw_ctx(q, hctx, i) {
 		if (e->ops.init_hctx) {
 			ret = e->ops.init_hctx(hctx, i);
@@ -482,11 +502,11 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 				return ret;
 			}
 		}
-		mutex_lock(&q->debugfs_mutex);
-		blk_mq_debugfs_register_sched_hctx(q, hctx);
-		mutex_unlock(&q->debugfs_mutex);
 	}
 
+	/* sched is initialized, it is ready to export it via debugfs */
+	blk_mq_sched_reg_debugfs(q);
+
 	return 0;
 
 err_free_map_and_rqs:
@@ -524,22 +544,17 @@ void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
 	unsigned long i;
 	unsigned int flags = 0;
 
-	queue_for_each_hw_ctx(q, hctx, i) {
-		mutex_lock(&q->debugfs_mutex);
-		blk_mq_debugfs_unregister_sched_hctx(hctx);
-		mutex_unlock(&q->debugfs_mutex);
+	/* 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);
 			hctx->sched_data = NULL;
 		}
 		flags = hctx->flags;
 	}
 
-	mutex_lock(&q->debugfs_mutex);
-	blk_mq_debugfs_unregister_sched(q);
-	mutex_unlock(&q->debugfs_mutex);
-
 	if (e->type->ops.exit_sched)
 		e->type->ops.exit_sched(e);
 	blk_mq_sched_tags_teardown(q, flags);