Description of problem:

/builddir/build/BUILD/ceph-12.2.4/src/mds/Locker.cc: 3793: FAILED assert(mds->is_rejoin() || mds->is_clientreplay() || mds->is_active() || mds->is_stopping())

 ceph version 12.2.4-6.el7cp (78f60b924802e34d44f7078029a40dbe6c0c922f) luminous (stable)
 1: (ceph::__ceph_assert_fail(char const*, char const*, int, char const*)+0x110) [0x55bba8bda2a0]
 2: (Locker::handle_lock(MLock*)+0x57) [0x55bba8a4a7c7]
 3: (Locker::dispatch(Message*)+0x85) [0x55bba8a565e5]
 4: (MDSRank::handle_deferrable_message(Message*)+0xbb4) [0x55bba88bd264]
 5: (MDSRank::_dispatch(Message*, bool)+0x1e3) [0x55bba88cab33]
 6: (MDSRankDispatcher::ms_dispatch(Message*)+0x15) [0x55bba88cb975]
 7: (MDSDaemon::ms_dispatch(Message*)+0xf3) [0x55bba88b4593]
 8: (DispatchQueue::entry()+0x792) [0x55bba8ec3d32]
 9: (DispatchQueue::DispatchThread::entry()+0xd) [0x55bba8c5fefd]
 10: (()+0x7dd5) [0x7f2098147dd5]
 11: (clone()+0x6d) [0x7f2097227b3d]
 NOTE: a copy of the executable, or `objdump -rdS <executable>` is needed to interpret this.


Version-Release number of selected component (if applicable):
 ceph version 12.2.4-6.el7cp

How reproducible:
1/1

Steps to Reproduce:
1. Configure cluster with 3 MDS (2 acitve and 1 standby)
2. Reduce the max mds to 1 
3. deactivate the 1 rank MDS's wait till mds stops.
4. Stop the MDS daemons of standby MDS
5. restart the active MDS wait till it comes active
6. Start the standby MDS
7. Increate max_mds to 2, MDS will be in starting state.
MDS was in starting state for more than 2 hrs, Tried to restart the MDS (which is in starting state), after service restart found the it is in starting state again and move d to resolve state.

Still the MDS is in resolve state, observed assert in MDS log.

Actual results:
MDS in resolve state, and fs state is degraded

Expected results:
MDS should become active and FS should be OK

Additional info: