Comment 19 for bug 1856871

I reproduced the behaviour using 5.5 upstream kernel by:

1) Mounting a loop device
2) Setup frace for all loop function for capture purposes
3) Then umount the loop device

trace_pipe reveal the following:
"umount-1850 [000] .... 471.727511: loop_release_xfer <-__loop_clr_fd"

As cascardo mentioned earlier it might be in the way that loop device are detached, now that I know what function to look at, I'll investigate further.