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SubjectRe: [PATCH v3 (resend)] block/loop: Serialize ioctl operations.
Hello, Ming Lei.

I'd like to hear your comment on this patch regarding the ordering of
stopping kernel thread.

> In order to enforce this strategy, this patch inversed
> loop_reread_partitions() and loop_unprepare_queue() in loop_clr_fd().
> I don't know whether it breaks something, but I don't have testcases.

Until 3.19, kthread_stop(lo->lo_thread) was called before
ioctl_by_bdev(bdev, BLKRRPART, 0) is called.
During 4.0 to 4.3, the loop module was using "kloopd" workqueue.
But since 4.4, loop_reread_partitions(lo, bdev) is called before
loop_unprepare_queue(lo) is called. And this patch is trying to change to
call loop_unprepare_queue() before loop_reread_partitions() is called.
Is there some reason we need to preserve current ordering?

Relevant commits:

commit b5dd2f6047ca108001328aac0e8588edd15f1778
block: loop: improve performance via blk-mq

commit e03a3d7a94e2485b6e2fa3fb630b9b3a30b65718
block: loop: use kthread_work

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