memstick/ms_block: simplify refcounting

Implement the ->free_disk method to free the msb_data structure only once
the last gendisk reference goes away instead of keeping a local refcount.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220215094514.3828912-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/memstick/core/ms_block.c

@@ -1943,22 +1943,6 @@ static void msb_io_work(struct work_struct *work)
 static DEFINE_IDR(msb_disk_idr); /*set of used disk numbers */
 static DEFINE_MUTEX(msb_disk_lock); /* protects against races in open/release */
 
-static int msb_bd_open(struct block_device *bdev, fmode_t mode)
-{
-	struct gendisk *disk = bdev->bd_disk;
-	struct msb_data *msb = disk->private_data;
-
-	dbg_verbose("block device open");
-
-	mutex_lock(&msb_disk_lock);
-
-	if (msb && msb->card)
-		msb->usage_count++;
-
-	mutex_unlock(&msb_disk_lock);
-	return 0;
-}
-
 static void msb_data_clear(struct msb_data *msb)
 {
 	kfree(msb->boot_page);
@@ -1968,33 +1952,6 @@ static void msb_data_clear(struct msb_data *msb)
 	msb->card = NULL;
 }
 
-static int msb_disk_release(struct gendisk *disk)
-{
-	struct msb_data *msb = disk->private_data;
-
-	dbg_verbose("block device release");
-	mutex_lock(&msb_disk_lock);
-
-	if (msb) {
-		if (msb->usage_count)
-			msb->usage_count--;
-
-		if (!msb->usage_count) {
-			disk->private_data = NULL;
-			idr_remove(&msb_disk_idr, msb->disk_id);
-			put_disk(disk);
-			kfree(msb);
-		}
-	}
-	mutex_unlock(&msb_disk_lock);
-	return 0;
-}
-
-static void msb_bd_release(struct gendisk *disk, fmode_t mode)
-{
-	msb_disk_release(disk);
-}
-
 static int msb_bd_getgeo(struct block_device *bdev,
 				 struct hd_geometry *geo)
 {
@@ -2003,6 +1960,17 @@ static int msb_bd_getgeo(struct block_device *bdev,
 	return 0;
 }
 
+static void msb_bd_free_disk(struct gendisk *disk)
+{
+	struct msb_data *msb = disk->private_data;
+
+	mutex_lock(&msb_disk_lock);
+	idr_remove(&msb_disk_idr, msb->disk_id);
+	mutex_unlock(&msb_disk_lock);
+
+	kfree(msb);
+}
+
 static blk_status_t msb_queue_rq(struct blk_mq_hw_ctx *hctx,
 				 const struct blk_mq_queue_data *bd)
 {
@@ -2096,10 +2064,9 @@ static void msb_start(struct memstick_dev *card)
 }
 
 static const struct block_device_operations msb_bdops = {
-	.open    = msb_bd_open,
-	.release = msb_bd_release,
-	.getgeo  = msb_bd_getgeo,
-	.owner   = THIS_MODULE
+	.owner		= THIS_MODULE,
+	.getgeo		= msb_bd_getgeo,
+	.free_disk	= msb_bd_free_disk, 
 };
 
 static const struct blk_mq_ops msb_mq_ops = {
@@ -2147,7 +2114,6 @@ static int msb_init_disk(struct memstick_dev *card)
 	set_capacity(msb->disk, capacity);
 	dbg("Set total disk size to %lu sectors", capacity);
 
-	msb->usage_count = 1;
 	msb->io_queue = alloc_ordered_workqueue("ms_block", WQ_MEM_RECLAIM);
 	INIT_WORK(&msb->io_work, msb_io_work);
 	sg_init_table(msb->prealloc_sg, MS_BLOCK_MAX_SEGS+1);
@@ -2229,7 +2195,7 @@ static void msb_remove(struct memstick_dev *card)
 	msb_data_clear(msb);
 	mutex_unlock(&msb_disk_lock);
 
-	msb_disk_release(msb->disk);
+	put_disk(msb->disk);
 	memstick_set_drvdata(card, NULL);
 }
 

drivers/memstick/core/ms_block.h

@@ -143,7 +143,6 @@ struct ms_boot_page {
 } __packed;
 
 struct msb_data {
-	unsigned int			usage_count;
 	struct memstick_dev		*card;
 	struct gendisk			*disk;
 	struct request_queue		*queue;