Whenever I run `mongo --host mongo3:27017 --eval 'db.serverStatus()'` this command hangs for a very long time (never managed to get reply).
mongo3 is a SECONDARY server in mongodb replica set. On PRIMARY and other SECONDARIES everything works as expected.

Output of the following command in attachment (gdb_2020-11-09_15-58-04.txt.xz):

gdb p $(pidof mongod) -batch -ex 'thread apply all bt' > gdb_`date +"%Y%m-%d_%H-%M-%S"`.txt

This is Gentoo Linux with 4.2.10 mongodb installed.

Another observation. I've tried to stop mongodb and it hanged with the following in logs:

2020-11-09T16:32:51.302+0300 I CONTROL [signalProcessingThread] got signal 15 (Terminated), will terminate after current cmd ends
2020-11-09T16:32:51.304+0300 I REPL [signalProcessingThread] Stepping down the ReplicationCoordinator for shutdown, waitTime: 10000ms
2020-11-09T16:32:51.309+0300 I SHARDING [signalProcessingThread] Shutting down the WaitForMajorityService
2020-11-09T16:32:51.313+0300 I CONTROL [signalProcessingThread] Shutting down the LogicalSessionCache
2020-11-09T16:32:51.316+0300 I CONTROL [LogicalSessionCacheRefresh] Failed to refresh session cache: ClientMarkedKilled: client has been killed
2020-11-09T16:32:51.320+0300 I CONTROL [LogicalSessionCacheReap] Failed to reap transaction table: ClientMarkedKilled: client has been killed
2020-11-09T16:32:51.321+0300 I NETWORK [signalProcessingThread] shutdown: going to close listening sockets...
2020-11-09T16:32:51.321+0300 I NETWORK [listener] removing socket file: /tmp/mongodb-27017.sock
2020-11-09T16:32:51.321+0300 I NETWORK [signalProcessingThread] Shutting down the global connection pool
2020-11-09T16:32:51.321+0300 I STORAGE [signalProcessingThread] Shutting down the FlowControlTicketholder
2020-11-09T16:32:51.321+0300 I - [signalProcessingThread] Stopping further Flow Control ticket acquisitions.
2020-11-09T16:32:51.321+0300 I STORAGE [signalProcessingThread] Shutting down the PeriodicThreadToAbortExpiredTransactions
2020-11-09T16:32:51.321+0300 I STORAGE [signalProcessingThread] Shutting down the PeriodicThreadToDecreaseSnapshotHistoryIfNotNeeded
2020-11-09T16:32:51.322+0300 I REPL [signalProcessingThread] Shutting down the ReplicationCoordinator
2020-11-09T16:32:51.322+0300 I REPL [signalProcessingThread] shutting down replication subsystems
2020-11-09T16:32:51.322+0300 I REPL [signalProcessingThread] Stopping replication reporter thread
2020-11-09T16:32:51.322+0300 I REPL [SyncSourceFeedback] SyncSourceFeedback error sending update to mongo1:27017: CallbackCanceled: Reporter no longer valid
2020-11-09T16:32:51.323+0300 I REPL [signalProcessingThread] Stopping replication fetcher thread
2020-11-09T16:32:51.324+0300 I REPL [signalProcessingThread] Stopping replication applier thread
2020-11-09T16:32:51.507+0300 I REPL [rsBackgroundSync] Replication producer stopped after oplog fetcher finished returning a batch from our sync source. Abandoning this batch of oplog entries and re-evaluating our sync source.
2020-11-09T16:32:51.508+0300 I REPL [rsBackgroundSync] Stopping replication producer

I've run gdb command (mentioned above) again and output is in gdb_2020-11-09_16-34-39.txt.xz.

After I've killed server with -9 and started again db.serverStatus() started to work.