On Thu, Jul 25, 2019 at 6:26 AM Cyril Hrubis <chrubis@suse.cz> wrote:
>
> This looks like mkfs.vfat got EBUSY after the loop device was
> succesfully umounted.

Hmm. Smells like the RCU-delaying got triggered again.

We have that "synchronize_rcu_expedited()" in namespace_unlock(),
which is so that everything should be done by the time we return to
user space.

Al, maybe that RCU synchronization should be after the mntput()s?

               Linus