Re: [PATCH v3] loop: Fix NULL pointer dereference in lo_rw_aio()

[Ming Lei]

On Mon, May 25, 2026 at 12:40:19PM +0900, Tetsuo Handa wrote:
> Some commit which was merged in the merge window for 7.1 broke the loop
> driver; a race window where lo_release() clears the backing file via
> __loop_clr_fd() despite some I/O requests are pending was introduced [1][2].
> 
> The exact commit which changed the behavior is not known due to lack of
> reproducer and timing dependent behavior, but it seems that we need to
> solve this problem in the loop driver despite there was no change for the
> loop driver during this merge window.
> 
> To close this race, try to flush pending I/O requests. However, calling
> drain_workqueue() from __loop_clr_fd() with disk->open_mutex held causes
> lockdep warnings [3][4]. We need to flush pending I/O requests without
> disk->open_mutex held.

No, please don't workaround before root cause.

No proof shows that the issue is in block layer or loop driver, the IO isn't
expected, you need to figure out why btrfs still issues IO after this loop
disk is closed by everyone and writeback is done.

https://syzkaller.appspot.com/x/log.txt?x=101e4702580000


Thanks,
Ming