restricting access in upgrading?

Hello,

I'm upgrading my postgresql once again and again there is this note in the
INSTALL file: "Caution: You must make sure that your database is not
updated in the middle of your backup. If necessary, bring down postmaster,
edit the permissions in file pg_hba.conf to allow only you on, then bring
postmaster back up." OK, I understand and I even can achieve this using only

local        all                                         password
pg_passwd_single

in my pg_hba.conf where pg_passwd_single is something I only know but this
makes it impossible to use pg_dumpall. So how should I obey the caution?

Ari