If we don't early-disable it, we can see a situation where when
handling invalidations wcfs calls open("@revX/bigfile/...") to upload
cache data there, go runtime tries to use epoll on that fd, and it gets
stuck as described in the commit referenced in comments.

In particular the deadlock was easy to trigger with nproc=1 environment
(either a VM with 1 cpu, or e.g. under `taskset -c 0`)

Bug reported by @romain.