This bug was initially created as a copy of Bug #2349077

I am copying this bug because: 
This needs to be backported to the 8.0 z-stream in addition to 8.1.


Description of problem:

Corresponding upstream tracker here: https://tracker.ceph.com/issues/69760

Essentially, the user was running a v18.2.1 cluster and hit BZ#2290580, which we know occurs when clients older than Reef are erroneously allowed to connect to the cluster when pg_upmap_primary, a strictly-Reef feature, is employed.

The user also hit BZ#2348970, which occurs when a pool is deleted and "phantom" pg_upmap_primary entries for that pool are left in the OSDMap. Therefore, the user cannot remove the pg_upmap_primary entries prior to upgrading from the broken encoder to the fixed encoder, which is the suggested workaround for BZ#2290580.

The idea for a fix is to provide the option to force-removal of a "phantom" pg_upmap_primary mapping, and potentially to relax the assertion in the OSDMap encoder.

The net effect: Although fixes for BZ#2290580 are already included in v18.2.4, the user still experiences difficulty if they hit the crash try to upgrade.

Version-Release number of selected component (if applicable):
v18.2.1