On 2021/12/23 0:56, Jens Axboe wrote:
> On 12/22/21 8:27 AM, Tetsuo Handa wrote:
>> The kernel test robot is reporting that xfstest can fail at
>>
>> umount ext2 on xfs
>> umount xfs
>>
>> sequence, for commit 322c4293ecc58110 ("loop: make autoclear operation
>> asynchronous") broke what commit ("loop: Make explicit loop device
>> destruction lazy") wanted to achieve.
>>
>> Although we cannot guarantee that nobody is holding a reference when
>> "umount xfs" is called, we should try to close a race window opened
>> by asynchronous autoclear operation.
>>
>> Try to make the autoclear operation upon close() synchronous, by calling
>> __loop_clr_fd() from current thread's task work rather than a WQ thread.
>
> Doesn't this potentially race with fput?
>
What race?
loop_schedule_rundown() is called from lo_release() from blkdev_put() from
blkdev_close() from __fput() from task_work_run(). And loop_schedule_rundown()
calls kobject_get(&bdev->bd_device.kobj) before put_device() from
blkdev_put_no_open() from blkdev_put() from blkdev_close() from __fput() from
task_work_run() calls kobject_put(&bdev->bd_device.kobj).
