Question: consult patch

[zhangwensheng (E)]

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@xxxxxxxxxx>
    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!