Re: [PATCH v4] fs/namespace: defer RCU sync for MNT_DETACH umount

[Christian Brauner]

>     So if there's some userspace process with a broken NFS server and it
>     does umount(MNT_DETACH) it will end up hanging every other
>     umount(MNT_DETACH) on the system because the dealyed_mntput_work
>     workqueue (to my understanding) cannot make progress.

Ok, "to my understanding" has been updated after going back and reading
the delayed work code. Luckily it's not as bad as I thought it is
because it's queued on system_wq which is multi-threaded so it's at
least not causing everyone with MNT_DETACH to get stuck. I'm still
skeptical how safe this all is.