[Bug] INFO: task hung in bdev_getblk in Linux kernel v6.15

[John]

Dear Linux Kernel Maintainers,

I hope this message finds you well.

I am writing to report a potential vulnerability I encountered during
testing of the Linux Kernel version v6.15.

Git Commit: 0ff41df1cb268fc69e703a08a57ee14ae967d0ca (tag: v6.15)

Bug Location:

Bug report: https://hastebin.com/share/xafazazeve.yaml

Complete log: https://hastebin.com/share/wopivucivi.perl

Entire kernel config:  https://hastebin.com/share/ajowibazak.ini

Root Cause Analysis:

The bug originates from bdev_getblk() in fs/buffer.c, where an invalid
1024-byte block size is requested on a device with a 2048-byte logical
block size. The function does not enforce block size consistency,
leading to downstream allocation failure in
ext4_reserve_inode_write(). This failure is not gracefully handled,
resulting in a persistent hang of the writeback worker thread, I/O
errors, and filesystem instability.

At present, I have not yet obtained a minimal reproducer for this
issue. However, I am actively working on reproducing it, and I will
promptly share any additional findings or a working reproducer as soon
as it becomes available.

Thank you very much for your time and attention to this matter. I
truly appreciate the efforts of the Linux kernel community.

Best regards,
John