[PATCH] refcounts for gendisks

Finally.  We use disk->dev.refcount as a gendisk refcount.  New helper -
get_disk(): atomic_inc on refcount.  get_gendisk() does it on return,
callers of get_gendisk() do put_disk() when they are done.

drivers/block/genhd.c

@@ -100,6 +100,8 @@ get_gendisk(dev_t dev, int *part)
 	read_lock(&gendisk_lock);
 	if (gendisks[major].get) {
 		disk = gendisks[major].get(minor);
+		if (disk)
+			get_disk(disk);
 		read_unlock(&gendisk_lock);
 		return disk;
 	}
@@ -109,6 +111,7 @@ get_gendisk(dev_t dev, int *part)
 			continue;
 		if (disk->first_minor + disk->minors <= minor)
 			continue;
+		get_disk(disk);
 		read_unlock(&gendisk_lock);
 		*part = minor - disk->first_minor;
 		return disk;
@@ -244,6 +247,12 @@ struct gendisk *alloc_disk(int minors)
 	return disk;
 }
 
+struct gendisk *get_disk(struct gendisk *disk)
+{
+	atomic_inc(&disk->disk_dev.refcount);
+	return disk;
+}
+
 void put_disk(struct gendisk *disk)
 {
 	if (disk)
@@ -251,4 +260,5 @@ void put_disk(struct gendisk *disk)
 }
 
 EXPORT_SYMBOL(alloc_disk);
+EXPORT_SYMBOL(get_disk);
 EXPORT_SYMBOL(put_disk);

drivers/block/ioctl.c

@@ -25,13 +25,17 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg *arg)
 	disk = get_gendisk(bdev->bd_dev, &part);
 	if (!disk)
 		return -ENXIO;
-	if (bdev != bdev->bd_contains)
+	if (bdev != bdev->bd_contains) {
+		put_disk(disk);
 		return -EINVAL;
+	}
 	if (part)
 		BUG();
 	part = p.pno;
-	if (part <= 0 || part >= disk->minors)
+	if (part <= 0 || part >= disk->minors) {
+		put_disk(disk);
 		return -EINVAL;
+	}
 
 	switch (a.op) {
 		case BLKPG_ADD_PARTITION:
@@ -42,34 +46,46 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg *arg)
 			    sizeof(long long) > sizeof(long)) {
 				long pstart = start, plength = length;
 				if (pstart != start || plength != length
-				    || pstart < 0 || plength < 0)
+				    || pstart < 0 || plength < 0) {
+					put_disk(disk);
 					return -EINVAL;
+				}
 			}
 
 			/* partition number in use? */
-			if (disk->part[part - 1].nr_sects != 0)
+			if (disk->part[part - 1].nr_sects != 0) {
+				put_disk(disk);
 				return -EBUSY;
+			}
 
 			/* overlap? */
 			for (i = 0; i < disk->minors - 1; i++) {
 				struct hd_struct *s = &disk->part[i];
 				if (!(start+length <= s->start_sect ||
-				      start >= s->start_sect + s->nr_sects))
+				      start >= s->start_sect + s->nr_sects)) {
+					put_disk(disk);
 					return -EBUSY;
+				}
 			}
 			/* all seems OK */
 			add_partition(disk, part, start, length);
+			put_disk(disk);
 			return 0;
 		case BLKPG_DEL_PARTITION:
-			if (disk->part[part - 1].nr_sects == 0)
+			if (disk->part[part - 1].nr_sects == 0) {
+				put_disk(disk);
 				return -ENXIO;
+			}
 
 			/* partition in use? Incomplete check for now. */
 			bdevp = bdget(MKDEV(disk->major, disk->first_minor) + part);
-			if (!bdevp)
+			if (!bdevp) {
+				put_disk(disk);
 				return -ENOMEM;
+			}
 			if (bd_claim(bdevp, &holder) < 0) {
 				bdput(bdevp);
+				put_disk(disk);
 				return -EBUSY;
 			}
 
@@ -80,8 +96,10 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg *arg)
 			delete_partition(disk, part);
 			bd_release(bdevp);
 			bdput(bdevp);
+			put_disk(disk);
 			return 0;
 		default:
+			put_disk(disk);
 			return -EINVAL;
 	}
 }
@@ -92,16 +110,25 @@ static int blkdev_reread_part(struct block_device *bdev)
 	struct gendisk *disk = get_gendisk(bdev->bd_dev, &part);
 	int res = 0;
 
-	if (!disk || disk->minors == 1 || bdev != bdev->bd_contains)
+	if (!disk)
 		return -EINVAL;
+	if (disk->minors == 1 || bdev != bdev->bd_contains) {
+		put_disk(disk);
+		return -EINVAL;
+	}
 	if (part)
 		BUG();
-	if (!capable(CAP_SYS_ADMIN))
+	if (!capable(CAP_SYS_ADMIN)) {
+		put_disk(disk);
 		return -EACCES;
-	if (down_trylock(&bdev->bd_sem))
+	}
+	if (down_trylock(&bdev->bd_sem)) {
+		put_disk(disk);
 		return -EBUSY;
+	}
 	res = rescan_partitions(disk, bdev);
 	up(&bdev->bd_sem);
+	put_disk(disk);
 	return res;
 }
 

fs/block_dev.c

@@ -542,6 +542,7 @@ int check_disk_change(struct block_device *bdev)
 		bdops->revalidate(dev);
 	if (disk && disk->minors > 1)
 		bdev->bd_invalidated = 1;
+	put_disk(disk);
 	return 1;
 }
 
@@ -553,7 +554,9 @@ int full_check_disk_change(struct block_device *bdev)
 		BUG();
 	down(&bdev->bd_sem);
 	if (check_disk_change(bdev)) {
-		rescan_partitions(get_gendisk(bdev->bd_dev, &n), bdev);
+		struct gendisk *disk = get_gendisk(bdev->bd_dev, &n);
+		rescan_partitions(disk, bdev);
+		put_disk(disk);
 		res = 1;
 	}
 	up(&bdev->bd_sem);
@@ -622,13 +625,18 @@ static int do_open(struct block_device *bdev, struct inode *inode, struct file *
 			struct block_device *disk;
 			disk = bdget(MKDEV(g->major, g->first_minor));
 			ret = -ENOMEM;
-			if (!disk)
+			if (!disk) {
+				put_disk(g);
 				goto out1;
+			}
 			ret = blkdev_get(disk, file->f_mode, file->f_flags, BDEV_RAW);
-			if (ret)
+			if (ret) {
+				put_disk(g);
 				goto out1;
+			}
 			bdev->bd_contains = disk;
 		}
+		put_disk(g);
 	}
 	if (bdev->bd_contains == bdev) {
 		int part;
@@ -643,8 +651,10 @@ static int do_open(struct block_device *bdev, struct inode *inode, struct file *
 
 		if (bdev->bd_op->open) {
 			ret = bdev->bd_op->open(inode, file);
-			if (ret)
+			if (ret) {
+				put_disk(g);
 				goto out2;
+			}
 		}
 		if (!bdev->bd_openers) {
 			struct backing_dev_info *bdi;
@@ -662,6 +672,7 @@ static int do_open(struct block_device *bdev, struct inode *inode, struct file *
 		}
 		if (bdev->bd_invalidated)
 			rescan_partitions(g, bdev);
+		put_disk(g);
 	} else {
 		down(&bdev->bd_contains->bd_sem);
 		bdev->bd_contains->bd_part_count++;
@@ -673,15 +684,17 @@ static int do_open(struct block_device *bdev, struct inode *inode, struct file *
 			inode->i_data.backing_dev_info =
 			   bdev->bd_inode->i_data.backing_dev_info =
 			   bdev->bd_contains->bd_inode->i_data.backing_dev_info;
-			if (!p->nr_sects) {
+			if (!(g->flags & GENHD_FL_UP) || !p->nr_sects) {
 				bdev->bd_contains->bd_part_count--;
 				up(&bdev->bd_contains->bd_sem);
+				put_disk(g);
 				ret = -ENXIO;
 				goto out2;
 			}
 			bdev->bd_queue = bdev->bd_contains->bd_queue;
 			bdev->bd_offset = p->start_sect;
 			bd_set_size(bdev, (loff_t) p->nr_sects << 9);
+			put_disk(g);
 		}
 		up(&bdev->bd_contains->bd_sem);
 	}

fs/partitions/check.c

@@ -616,6 +616,7 @@ char *partition_name(dev_t dev)
 	dname->name = NULL;
 	if (hd)
 		dname->name = disk_name(hd, part, dname->namebuf);
+	put_disk(hd);
 	if (!dname->name) {
 		sprintf(dname->namebuf, "[dev %s]", kdevname(to_kdev_t(dev)));
 		dname->name = dname->namebuf;

include/linux/genhd.h

@@ -266,6 +266,7 @@ extern void add_partition(struct gendisk *, int, sector_t, sector_t);
 extern void delete_partition(struct gendisk *, int);
 
 extern struct gendisk *alloc_disk(int minors);
+extern struct gendisk *get_disk(struct gendisk *disk);
 extern void put_disk(struct gendisk *disk);
 
 /* will go away */
@@ -273,9 +274,11 @@ extern void blk_set_probe(int major, struct gendisk *(p)(int));
 
 static inline unsigned int disk_index (kdev_t dev)
 {
-	int part;
+	int part, res;
 	struct gendisk *g = get_gendisk(kdev_t_to_nr(dev), &part);
-	return g ? (minor(dev) >> g->minor_shift) : 0;
+	res = g ? (minor(dev) >> g->minor_shift) : 0;
+	put_disk(g);
+	return res;
 }
 
 #endif