blk: reuse lookup_sem to serialize partition operations

hulk inclusion
category: bugfix
bugzilla: 55097 https://gitee.com/openeuler/kernel/issues/I4DDEL

-------------------------------------------------

Now there no protection between partition operations (e.g, partition
rescan) and delete_partition() in del_gendisk(), so the following
scenario is possible:

CPU 1

blkdev_ioctl                   del_gendisk
  blkdev_reread_part
    lock bd_mutex
      drop_partitions
        check_partition
                                 lock lookup_sem
				 // for each partition
				 deletion_partion

        // for each partition
        add_partition

The newly added partitions, the device files (e.g, /dev/sdXN)
and the symlinks in /sys/class/block will be left behind. If
the deleted disk is online again, the scan of partition will
fail with the following error:

  sysfs: cannot create duplicate filename '/class/block/sdaN'
  sdX: pN could not be added: 17

Vanilla kernel tries to fix that by commit c76f48eb
("block: take bd_mutex around delete_partitions in del_gendisk"),
but it introduces dead-lock for nbd/loop/xen-frontblk drivers.
These in-tree drivers can be fixed, but there may be other affected
block drivers, especially the out-of-tree ones, so fixing it in
another way.

Two methods are considered. The first is waiting for the end
of partition operations in del_gendisk(). It is OK but it needs
adding new fields in gendisk (bool & wait_queue_head_t). The second
is reusing lookup_sem and GENHD_FL_UP to serialize partition operations
and del_gendisk(). Now the latter is chose and here are the details.

There are six partition operations:

(1) add_partition() in blkpg_ioctl()
(2) deletion_partion() in blkpg_ioctl()
(3) resize in blkpg_ioctl()
(4) partition rescan and revalidate in bdev_disk_changed()
(5) deletion_partion() in del_gendisk()

op (1)~(4) already take bd_mutex, so using down_read() to
serialize with down_write() in del_gendisk() is OK. op (3)
only updates the values in hd_struct, so no lock is needed,
because it already increase the ref of hd_struct.

lookup_sem is used to prevent a newly-created blocking device inode from
associating with a deleting gendisk, and the locking order is:

  part->bd_mutex -> disk->lookup_sem
    or
  whole->bd_mutex -> disk->lookup_sem

Now it is also used to serialize the partition operations and the new
locking order will be:

  part->bd_mutex -> whole->bd_mutex -> disk->lookup_sem

and it is OK.
Signed-off-by: NYu Kuai <yukuai3@huawei.com>
Reviewed-by: NHou Tao <houtao1@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

block/partitions/core.c

@@ -523,6 +523,7 @@ int bdev_add_partition(struct block_device *bdev, int partno,
 	int ret;
 
 	mutex_lock(&bdev->bd_mutex);
+	down_read(&disk->lookup_sem);
 	if (!(disk->flags & GENHD_FL_UP)) {
 		ret = -ENXIO;
 		goto out;
@@ -537,6 +538,7 @@ int bdev_add_partition(struct block_device *bdev, int partno,
 			ADDPART_FLAG_NONE, NULL);
 	ret = PTR_ERR_OR_ZERO(part);
 out:
+	up_read(&disk->lookup_sem);
 	mutex_unlock(&bdev->bd_mutex);
 	return ret;
 }
@@ -553,6 +555,7 @@ int bdev_del_partition(struct block_device *bdev, int partno)
 
 	mutex_lock(&bdevp->bd_mutex);
 	mutex_lock_nested(&bdev->bd_mutex, 1);
+	down_read(&bdev->bd_disk->lookup_sem);
 
 	ret = -ENXIO;
 	part = disk_get_part(bdev->bd_disk, partno);
@@ -569,6 +572,7 @@ int bdev_del_partition(struct block_device *bdev, int partno)
 	delete_partition(part);
 	ret = 0;
 out_unlock:
+	up_read(&bdev->bd_disk->lookup_sem);
 	mutex_unlock(&bdev->bd_mutex);
 	mutex_unlock(&bdevp->bd_mutex);
 	bdput(bdevp);

fs/block_dev.c

@@ -1427,14 +1427,16 @@ int bdev_disk_changed(struct block_device *bdev, bool invalidate)
 	int ret;
 
 	lockdep_assert_held(&bdev->bd_mutex);
-
-	if (!(disk->flags & GENHD_FL_UP))
-		return -ENXIO;
+	down_read(&disk->lookup_sem);
+	if (!(disk->flags & GENHD_FL_UP)) {
+		ret = -ENXIO;
+		goto out;
+	}
 
 rescan:
 	ret = blk_drop_partitions(bdev);
 	if (ret)
-		return ret;
+		goto out;
 
 	clear_bit(GD_NEED_PART_SCAN, &disk->state);
 
@@ -1469,6 +1471,8 @@ int bdev_disk_changed(struct block_device *bdev, bool invalidate)
 		kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
 	}
 
+out:
+	up_read(&disk->lookup_sem);
 	return ret;
 }
 /*