CVE-2025-40125

In the Linux kernel, the following vulnerability has been resolved:

blk-mq: check kobject state_in_sysfs before deleting in blk_mq_unregister_hctx

In __blk_mq_update_nr_hw_queues() the return value of
blk_mq_sysfs_register_hctxs() is not checked. If sysfs creation for hctx
fails, later changing the number of hw_queues or removing disk will
trigger the following warning:

  kernfs: can not remove 'nr_tags', no directory
  WARNING: CPU: 2 PID: 637 at fs/kernfs/dir.c:1707 kernfs_remove_by_name_ns+0x13f/0x160
  Call Trace:
   remove_files.isra.1+0x38/0xb0
   sysfs_remove_group+0x4d/0x100
   sysfs_remove_groups+0x31/0x60
   __kobject_del+0x23/0xf0
   kobject_del+0x17/0x40
   blk_mq_unregister_hctx+0x5d/0x80
   blk_mq_sysfs_unregister_hctxs+0x94/0xd0
   blk_mq_update_nr_hw_queues+0x124/0x760
   nullb_update_nr_hw_queues+0x71/0xf0 [null_blk]
   nullb_device_submit_queues_store+0x92/0x120 [null_blk]

kobjct_del() was called unconditionally even if sysfs creation failed.
Fix it by checkig the kobject creation statusbefore deleting it.