I saw rocks storage deadlock when trying to acquire RocksEngine::_entryMapMutex twice. Here is the call stack
#7 mongo::RocksEngine::getIndexColumnFamily at src/mongo/db/storage/rocks/rocks_engine.cpp:224
#8 mongo::RocksCollectionCatalogEntry::removeIndex at src/mongo/db/storage/rocks/rocks_collection_catalog_entry.cpp:121
#9 mongo::RocksEngine::_dropCollection_inlock at src/mongo/db/storage/rocks/rocks_engine.cpp:348
#10 mongo::RocksEngine::dropDatabase at src/mongo/db/storage/rocks/rocks_engine.cpp:188
In dropDatabase(), _entryMapMutex is already acquired but in getIndexColumnFamily() it tries to acquire _entryMapMutex agin.