block: fix deadlock between bd_link_disk_holder and partition scan

'open_mutex' of gendisk is used to protect open/close block devices. But
in bd_link_disk_holder(), it is used to protect the creation of symlink
between holding disk and slave bdev, which introduces some issues.

When bd_link_disk_holder() is called, the driver is usually in the process
of initialization/modification and may suspend submitting io. At this
time, any io hold 'open_mutex', such as scanning partitions, can cause
deadlocks. For example, in raid:

T1                              T2
bdev_open_by_dev
 lock open_mutex [1]
 ...
  efi_partition
  ...
   md_submit_bio
				md_ioctl mddev_syspend
				  -> suspend all io
				 md_add_new_disk
				  bind_rdev_to_array
				   bd_link_disk_holder
				    try lock open_mutex [2]
    md_handle_request
     -> wait mddev_resume

T1 scan partition, T2 add a new device to raid. T1 waits for T2 to resume
mddev, but T2 waits for open_mutex held by T1. Deadlock occurs.

Fix it by introducing a local mutex 'blk_holder_mutex' to replace
'open_mutex'.

Fixes: 1b0a2d95 ("md: use new apis to suspend array for ioctls involed array reconfiguration")
Reported-by:  <mgperkow@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218459


Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20240221090122.1281868-1-linan666@huaweicloud.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>