client: request next osdmap for blacklisted client
In Luminous version, we found blacklisted client would never get rid of blacklisted flag if network was down for some time and MDS evicted this client session after timeout.
Here are some simple steps to reproduce:
1. Add a client to blacklist via "ceph osd blacklist add" command.
2. Wait for session timeout, MDS will evict this client session and then client will close its MDS session too.
3. Remove this client from blacklist via "ceph osd blacklist [rm|clear]" command.
Now there is no blacklisted entry, but this client's blacklisted flag is still true, so client is still not working.
The root cause is that when client became blacklisted, it did't subscribe next osdmap. So when it was removed from blacklist by expiration or commandline, it didn't get updated osdmap which is the only way for the client to reset its blacklisted flag.