Jann Horn [off-list ref] wrote:

(And as in the other case, the s->s_count increment will probably have
to be moved above the add_watch_to_object(), unless you hold the
sb_lock around it?)

It shouldn't matter as I'm holding s->s_umount across the add and increment.
That prevents the watch from being removed: watch_sb() would have to get the
lock first to do that.  It also deactivate_locked_super() from removing all
the watchers.

I can move it before, but I probably have to drop s_umount before I can call
put_super().

David