Ceph » CephFS

the new assert for wip-10057 would trigger this.

this looks like a corner case is the session close + reopen sequence. the client clears its seq state but the mds hasn't yet... but iirc the client isn't supposed to do that until it gets a positive "i closed this session" reply from the mds. :/

Hmm, the client only calls _closed_mds_session if:
1) it gets back a session close
2) the session goes stale
2a) which is set only if we get a remote reset while the session is open
3) it gets a remote reset while the state is closing or opening

Although it will also call mark_down() on the ConnectionRef of MDSes
1) which have CommandOps in progress and are named as laggy or nonexistent in the map
2) which are listed as not up, or whose gid does not match the current incarnation of that rank

So yeah, maybe if there are MDSes failing back and forth and we close a session without the MDS seeing the maps which forced it? If so I think this is related to #10080, although looking at the resetcheck policies I don't think the fix for that will have an impact here.

Yes — the related issue chain has been seen a few times, more recently.