Question: consult patch

["zhangwensheng (E)" <zhangwensheng@huaweicloud.com>]

Hi Lee ：
     I saw your patch because of CVE-2022-20158, the patch like below:

---
     mm: backing-dev: Take a reference to the bdi in use to prevent UAF

     KASAN reports a reproducible issue in the BDI handling code due to a
     dereference of a previously freed pointer to 'struct backing_dev_info'
     in bdi_unregister().

     Because of a distinct lack of locking and/or reference taking,
     blk_cleanup_queue() puts the final taken reference to the bdi, which
     is then promptly freed by release_bdi().  However, del_gendisk() calls
     bdi_unregister() after the fact, which then attempts to dereference
     it causing the kernel to panic.

     Bug: 182815710
     Signed-off-by: Lee Jones <lee.jones@linaro.org>
     Change-Id: Iaf3dadf3b983a4b7d74d4e273fc676350cfc387f
---

     I am sorry that I have some questions for this patch. According to
     my analysis, I failed to find the relevant process may lead to null
     pointer reference. can you show me "KASAN reports a reproducible issue"
     that what the problem is?  thank you very much!