sr: implement ->free_disk to simplify refcounting

Simplify the refcounting and remove the need to clear disk->private_data
by implementing the ->free_disk method.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20220308055200.735835-9-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Christoph Hellwig

drivers/scsi/sr.c

@@ -109,11 +109,6 @@ static DEFINE_SPINLOCK(sr_index_lock);
 
 static struct lock_class_key sr_bio_compl_lkclass;
 
-/* This semaphore is used to mediate the 0->1 reference get in the
- * face of object destruction (i.e. we can't allow a get on an
- * object after last put) */
-static DEFINE_MUTEX(sr_ref_mutex);
-
 static int sr_open(struct cdrom_device_info *, int);
 static void sr_release(struct cdrom_device_info *);
 
@@ -143,8 +138,6 @@ static const struct cdrom_device_ops sr_dops = {
 	.capability		= SR_CAPABILITIES,
 };
 
-static void sr_kref_release(struct kref *kref);
-
 static inline struct scsi_cd *scsi_cd(struct gendisk *disk)
 {
 	return disk->private_data;
@@ -163,38 +156,6 @@ static int sr_runtime_suspend(struct device *dev)
 		return 0;
 }
 
-/*
- * The get and put routines for the struct scsi_cd.  Note this entity
- * has a scsi_device pointer and owns a reference to this.
- */
-static inline struct scsi_cd *scsi_cd_get(struct gendisk *disk)
-{
-	struct scsi_cd *cd = NULL;
-
-	mutex_lock(&sr_ref_mutex);
-	if (disk->private_data == NULL)
-		goto out;
-	cd = scsi_cd(disk);
-	kref_get(&cd->kref);
-	if (scsi_device_get(cd->device)) {
-		kref_put(&cd->kref, sr_kref_release);
-		cd = NULL;
-	}
- out:
-	mutex_unlock(&sr_ref_mutex);
-	return cd;
-}
-
-static void scsi_cd_put(struct scsi_cd *cd)
-{
-	struct scsi_device *sdev = cd->device;
-
-	mutex_lock(&sr_ref_mutex);
-	kref_put(&cd->kref, sr_kref_release);
-	scsi_device_put(sdev);
-	mutex_unlock(&sr_ref_mutex);
-}
-
 static unsigned int sr_get_events(struct scsi_device *sdev)
 {
 	u8 buf[8];
@@ -522,15 +483,13 @@ static void sr_revalidate_disk(struct scsi_cd *cd)
 
 static int sr_block_open(struct block_device *bdev, fmode_t mode)
 {
-	struct scsi_cd *cd;
-	struct scsi_device *sdev;
+	struct scsi_cd *cd = cd = scsi_cd(bdev->bd_disk);
+	struct scsi_device *sdev = cd->device;
 	int ret = -ENXIO;
 
-	cd = scsi_cd_get(bdev->bd_disk);
-	if (!cd)
-		goto out;
+	if (scsi_device_get(cd->device))
+		return -ENXIO;
 
-	sdev = cd->device;
 	scsi_autopm_get_device(sdev);
 	if (bdev_check_media_change(bdev))
 		sr_revalidate_disk(cd);
@@ -541,9 +500,7 @@ static int sr_block_open(struct block_device *bdev, fmode_t mode)
 
 	scsi_autopm_put_device(sdev);
 	if (ret)
-		scsi_cd_put(cd);
-
-out:
+		scsi_device_put(cd->device);
 	return ret;
 }
 
@@ -555,7 +512,7 @@ static void sr_block_release(struct gendisk *disk, fmode_t mode)
 	cdrom_release(&cd->cdi, mode);
 	mutex_unlock(&cd->lock);
 
-	scsi_cd_put(cd);
+	scsi_device_put(cd->device);
 }
 
 static int sr_block_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
@@ -595,18 +552,24 @@ static int sr_block_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
 static unsigned int sr_block_check_events(struct gendisk *disk,
 					  unsigned int clearing)
 {
-	unsigned int ret = 0;
-	struct scsi_cd *cd;
+	struct scsi_cd *cd = disk->private_data;
 
-	cd = scsi_cd_get(disk);
-	if (!cd)
+	if (atomic_read(&cd->device->disk_events_disable_depth))
 		return 0;
+	return cdrom_check_events(&cd->cdi, clearing);
+}
 
-	if (!atomic_read(&cd->device->disk_events_disable_depth))
-		ret = cdrom_check_events(&cd->cdi, clearing);
+static void sr_free_disk(struct gendisk *disk)
+{
+	struct scsi_cd *cd = disk->private_data;
 
-	scsi_cd_put(cd);
-	return ret;
+	spin_lock(&sr_index_lock);
+	clear_bit(MINOR(disk_devt(disk)), sr_index_bits);
+	spin_unlock(&sr_index_lock);
+
+	unregister_cdrom(&cd->cdi);
+	mutex_destroy(&cd->lock);
+	kfree(cd);
 }
 
 static const struct block_device_operations sr_bdops =
@@ -617,6 +580,7 @@ static const struct block_device_operations sr_bdops =
 	.ioctl		= sr_block_ioctl,
 	.compat_ioctl	= blkdev_compat_ptr_ioctl,
 	.check_events	= sr_block_check_events,
+	.free_disk	= sr_free_disk,
 };
 
 static int sr_open(struct cdrom_device_info *cdi, int purpose)
@@ -660,8 +624,6 @@ static int sr_probe(struct device *dev)
 	if (!cd)
 		goto fail;
 
-	kref_init(&cd->kref);
-
 	disk = __alloc_disk_node(sdev->request_queue, NUMA_NO_NODE,
 				 &sr_bio_compl_lkclass);
 	if (!disk)
@@ -727,17 +689,17 @@ static int sr_probe(struct device *dev)
 	sr_revalidate_disk(cd);
 
 	error = device_add_disk(&sdev->sdev_gendev, disk, NULL);
-	if (error) {
-		kref_put(&cd->kref, sr_kref_release);
-		goto fail;
-	}
+	if (error)
+		goto unregister_cdrom;
 
 	sdev_printk(KERN_DEBUG, sdev,
 		    "Attached scsi CD-ROM %s\n", cd->cdi.name);
 	scsi_autopm_put_device(cd->device);
 
 	return 0;
 
+unregister_cdrom:
+	unregister_cdrom(&cd->cdi);
 fail_minor:
 	spin_lock(&sr_index_lock);
 	clear_bit(minor, sr_index_bits);
@@ -1009,48 +971,14 @@ static int sr_read_cdda_bpc(struct cdrom_device_info *cdi, void __user *ubuf,
 	return ret;
 }
 
-
-/**
- *	sr_kref_release - Called to free the scsi_cd structure
- *	@kref: pointer to embedded kref
- *
- *	sr_ref_mutex must be held entering this routine.  Because it is
- *	called on last put, you should always use the scsi_cd_get()
- *	scsi_cd_put() helpers which manipulate the semaphore directly
- *	and never do a direct kref_put().
- **/
-static void sr_kref_release(struct kref *kref)
-{
-	struct scsi_cd *cd = container_of(kref, struct scsi_cd, kref);
-	struct gendisk *disk = cd->disk;
-
-	spin_lock(&sr_index_lock);
-	clear_bit(MINOR(disk_devt(disk)), sr_index_bits);
-	spin_unlock(&sr_index_lock);
-
-	unregister_cdrom(&cd->cdi);
-
-	disk->private_data = NULL;
-
-	put_disk(disk);
-
-	mutex_destroy(&cd->lock);
-
-	kfree(cd);
-}
-
 static int sr_remove(struct device *dev)
 {
 	struct scsi_cd *cd = dev_get_drvdata(dev);
 
 	scsi_autopm_get_device(cd->device);
 
 	del_gendisk(cd->disk);
-	dev_set_drvdata(dev, NULL);
-
-	mutex_lock(&sr_ref_mutex);
-	kref_put(&cd->kref, sr_kref_release);
-	mutex_unlock(&sr_ref_mutex);
+	put_disk(cd->disk);
 
 	return 0;
 }

drivers/scsi/sr.h

@@ -18,7 +18,6 @@
 #ifndef _SR_H
 #define _SR_H
 
-#include <linux/kref.h>
 #include <linux/mutex.h>
 
 #define MAX_RETRIES	3
@@ -51,9 +50,6 @@ typedef struct scsi_cd {
 
 	struct cdrom_device_info cdi;
 	struct mutex lock;
-	/* We hold gendisk and scsi_device references on probe and use
-	 * the refs on this kref to decide when to release them */
-	struct kref kref;
 	struct gendisk *disk;
 } Scsi_CD;