[PATCH v4] block/loop: Serialize ioctl operations.

[Tetsuo Handa]

On 2018/09/24 7:03, Ming Lei wrote:
> On Sat, Sep 22, 2018 at 09:39:02PM +0900, Tetsuo Handa wrote:
>> 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?
> 
> IMO, both the two orders are fine, and what matters is that 'lo->lo_state'
> is updated before loop_reread_partitions(), then any IO from loop_reread_partitions
> will be failed, so it shouldn't be a big deal wrt. the order between
> loop_reread_partitions() and loop_unprepare_queue().

OK. Thank you. Here is v4 patch (only changelog was updated).
Andrew, can we test this patch in the -mm tree?