Ceph

I'm not entirely clear on how the monmap subscriptions work, but it
looks from the log as if

OSD::_maybe_boot with

osdmap->get_epoch() 0,
oldest 1, newset == 253 (_maybe_boot mon has osdmaps 1..253)

causes maybe_boot to fall through to the else branch at the end
osdmap_subscribe(oldest - 1, true);

osdmap_subscribe then observes osdmap->get_epoch() >= (oldest - 1) and
skips the subscription causing boot to hang.

The check in osdmap_subscribe was not present before
4584f60653bee0305e85418323d80332ceecd0cf.